Association between serum phospholipid fatty acid levels and adiposity in Mexican women

      Fatty acids (FAs) have been postulated to impact adiposity, but few epidemiological studies addressing this hypothesis have been conducted. This study investigated the association between serum phospholipid FAs (S-PLFAs) and indicators of obesity. BMI and waist-to-hip ratio (WHR) were collected from 372 healthy Mexican women included as controls in a case-control study. S-PLFA percentages were determined through gas chromatography. Desaturation indices, SCD-16, SCD-18, FA desaturase (FADS)1, and FADS2, biomarkers of endogenous metabolism, were proxied respectively as 16:1n-7/16:0, 18:1n-9/18:0, 20:4n-6/20:3n-6, and 22:6n-3/20:5n-3. Multiple linear regressions adjusted for relevant confounders and corrected for multiple testing were conducted to determine the association between S-PLFA, desaturation indices, and indicators of adiposity. SCD-16 (β = 0.034, P = 0.001, q = 0.014), palmitoleic acid (β = 0.031, P = 0.001, q = 0.014), and dihomo-γ-linolenic acid (β = 0.043, P = 0.000, q = 0.0002) were positively associated with BMI. Total n-6 PUFAs (β = 1.497, P = 0.047, q = 0.22) and the ratio of n-6/n-3 PUFAs (β = 0.034, P = 0.040, q = 0.19) were positively associated with WHR, while odd-chain FAs (pentadecanoic and heptadecanoic acid) showed negative associations with all the adiposity indicators. In conclusion, increased endogenous synthesis of palmitoleic acid and a high n-6/n-3 ratio are associated with increased adiposity, while odd-chain FAs are associated with decreased adiposity. Further studies are needed to determine the potential causality behind these associations.
      The obesity pandemic with associated comorbidities, such as respiratory and cardiovascular diseases, cancers, and other chronic diseases, is expanding worldwide (
      • Di Cesare M.
      • Bentham J.
      • Stevens G.A.
      • Zhou B.
      • Danaei G.
      • Lu Y.
      • Bixby H.
      • Cowan M.J.
      • Riley L.M.
      • Hajifathalian K.
      Trends in adult body-mass index in 200 countries from 1975 to 2014: a pooled analysis of 1698 population-based measurement studies with 19.2 million participants.
      ). The situation is worsening in the developing world, with countries such as Mexico exhibiting a concerning proportion of obese individuals (
      • Barquera S.
      • Campos I.
      • Rivera J.A.
      Mexico attempts to tackle obesity: the process, results, push backs and future challenges.
      ). According to recent estimates, approximately 65.3% of Mexican women are overweight or obese (
      • Di Cesare M.
      • Bentham J.
      • Stevens G.A.
      • Zhou B.
      • Danaei G.
      • Lu Y.
      • Bixby H.
      • Cowan M.J.
      • Riley L.M.
      • Hajifathalian K.
      Trends in adult body-mass index in 200 countries from 1975 to 2014: a pooled analysis of 1698 population-based measurement studies with 19.2 million participants.
      ). Further, according to recent projections, more than 90% of Mexican women are at risk of becoming overweight or obese by 2050, with profound consequences on noncommunicable disease incidence and placing greater burden on the health system (
      • Rtveladze K.
      • Marsh T.
      • Barquera S.
      • Sanchez Romero L.M.
      • Levy D.
      • Melendez G.
      • Webber L.
      • Kilpi F.
      • McPherson K.
      • Brown M.
      Obesity prevalence in Mexico: impact on health and economic burden.
      ).
      The global increase in obesity is predominantly attributed to the so-called obesogenic environment, which encompasses an increase in dietary energy intake and higher intake of added monosaccharides and saturated and trans fats, along with an unprecedented shift in energy expenditure patterns with a global decrease in physical activity and an increase in sedentary behaviors (
      • Popkin B.M.
      • Adair L.S.
      • Ng S.W.
      Global nutrition transition and the pandemic of obesity in developing countries.
      ). The introduction of fast-food chains and the dissemination of Westernized dietary habits seem to be a marker of the increasing prevalence of obesity (
      • Stender S.
      • Astrup A.
      • Dyerberg J.
      Ruminant and industrially produced trans fatty acids: health aspects.
      ).
      Several epidemiological studies have examined the relationship between dietary fat and FAs estimated through dietary questionnaires and obesity, but the epidemiological evidence remains insufficient. Melanson, Astrup, and Donahoo (
      • Melanson E.L.
      • Astrup A.
      • Donahoo W.T.
      The relationship between dietary fat and fatty acid intake and body weight, diabetes, and the metabolic syndrome.
      ) summarized interventional prospective cohorts and cross-sectional studies and reported mitigated associations, although increased intakes of saturated FAs (SFAs), MUFAs, and trans FAs (TFAs) were associated with slightly higher risk of obesity, while a minor protective effect was reported for PUFAs.
      Nutritional epidemiology is limited by the assessment of dietary FAs through food-frequency questionnaires or other dietary assessment methods (
      • Bingham S.A.
      • Day N.E.
      • Luben R.
      • Ferrari P.
      • Slimani N.
      • Norat T.
      • Clavel-Chapelon F.
      • Kesse E.
      • Nieters A.
      • Boeing H.
      Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study.
      ). FA content of adipose tissue, triacylglycerol, phospholipid, and cholesterol ester fractions of serum, plasma, or erythrocyte membranes reflect long-term to short-term intake of dietary FAs (
      • Baylin A.
      • Campos H.
      The use of fatty acid biomarkers to reflect dietary intake.
      ). As the half-life of FAs in adipose tissue is 2 years long, adipose tissue FA composition can provide major information about long-term intake (
      • Katan M.B.
      • Deslypere J.P.
      • van Birgelen A.P.
      • Penders M.
      • Zegwaard M.
      Kinetics of the incorporation of dietary fatty acids into serum cholesteryl esters, erythrocyte membranes, and adipose tissue: an 18-month controlled study.
      ). However, most ongoing epidemiological studies have available blood fractions instead of adipose tissue samples. Triacylglycerol fractions in blood are influenced by the type and amount of fat consumed during recent meals; thus, they are not the most appropriate markers of usual diet. The FA composition of serum, plasma, or erythrocyte membrane phospholipid fraction reflects medium-term (weeks to months) intakes of some FAs or food sources, particularly for FAs that are not endogenously synthesized, industrial TFAs (ITFAs) and n-3 PUFAs (
      • Baylin A.
      • Campos H.
      The use of fatty acid biomarkers to reflect dietary intake.
      ,
      • Chajès V.
      • Biessy C.
      • Byrnes G.
      • Deharveng G.
      • Saadatian-Elahi M.
      • Jenab M.
      • Peeters P.H.
      • Ocke M.
      • Bueno-de-Mesquita H.B.
      • Johansson I.
      Ecological-level associations between highly processed food intakes and plasma phospholipid elaidic acid concentrations: results from a cross-sectional study within the European prospective investigation into cancer and nutrition (EPIC).
      ,
      • Saadatian-Elahi M.
      • Slimani N.
      • Chajes V.
      • Jenab M.
      • Goudable J.
      • Biessy C.
      • Ferrari P.
      • Byrnes G.
      • Autier P.
      • Peeters P.H.
      Plasma phospholipid fatty acid profiles and their association with food intakes: results from a cross-sectional study within the European Prospective Investigation into Cancer and Nutrition.
      ). Besides FAs derived from dietary sources, desaturation indices can be determined in plasma or serum phospholipids as the ratio of products to substrates and are used as surrogate biomarkers of endogenous lipogenesis of FAs (
      • Chajès V.
      • Joulin V.
      • Clavel-Chapelon F.
      The fatty acid desaturation index of blood lipids, as a biomarker of hepatic stearoyl-CoA desaturase expression, is a predictive factor of breast cancer risk.
      ). Thus, serum (or plasma) phospholipid FA (S-PLFA) composition can be considered as a convenient alternative for the assessment of medium-term usual intake and metabolism of FAs in large-scale epidemiologic studies (
      • Thiébaut A.C.
      • Rotival M.
      • Gauthier E.
      • Lenoir G.M.
      • Boutron-Ruault M.C.
      • Joulin V.
      • Clavel-Chapelon F.
      • Chajes V.
      Correlation between serum phospholipid fatty acids and dietary intakes assessed a few years earlier.
      ,
      • Hjartåker A.
      • Lund E.
      • Bjerve K.S.
      Serum phospholipid fatty acid composition and habitual intake of marine foods registered by a semi-quantitative food frequency questionnaire.
      ,
      • Brevik A.
      • Veierod M.B.
      • Drevon C.A.
      • Andersen L.F.
      Evaluation of the odd fatty acids 15:0 and 17:0 in serum and adipose tissue as markers of intake of milk and dairy fat.
      ,
      • Wolk A.
      • Furuheim M.
      • Vessby B.
      Fatty acid composition of adipose tissue and serum lipids are valid biological markers of dairy fat intake in men.
      ).
      Few studies have investigated the association between biomarkers of FAs, FA metabolism, and obesity. One study conducted within the European EPIC cohort has reported an association between high percentages of plasma phospholipid ITFAs and increased risk of weight gain during the follow-up, particularly in women (
      • Chajès V.
      • Biessy C.
      • Ferrari P.
      • Romieu I.
      • Freisling H.
      • Huybrechts I.
      • Scalbert A.
      • Bueno de Mesquita B.
      • Romaguera D.
      • Gunter M.J.
      Plasma elaidic acid level as biomarker of industrial trans fatty acids and risk of weight change: report from the EPIC Study.
      ). A recent review by Mika and Sledzinski (
      • Mika A.
      • Sledzinski T.
      Alterations of specific lipid groups in serum of obese humans: a review.
      ) reported a trend for a positive association between obesity and serum SFAs, MUFAs, and TFAs, and a negative association for odd-chain and branched SFAs. Endogenous production of FAs through the desaturation activity influences the relative levels of individual S-PLFAs. The desaturation activity is surrogated with the desaturation indices, SCD-16 and SCD-18, for the conversion of SFAs into MUFAs, and FA desaturase (FADS)1 and FADS2 for the introduction of additional double bonds to n-3 and n-6 PUFAs. SCD-16 has been reported to be positively associated with obesity indicators and body fatness, while the associations are mitigated for SCD-18 in cross-sectional studies (
      • Do H.J.
      • Chung H.K.
      • Moon J.
      • Shin M.J.
      Relationship between the estimates of desaturase activities and cardiometabolic phenotypes in Koreans.
      ,
      • Warensjö E.
      • Rosell M.
      • Hellenius M.L.
      • Vessby B.
      • De Faire U.
      • Riserus U.
      Associations between estimated fatty acid desaturase activities in serum lipids and adipose tissue in humans: links to obesity and insulin resistance.
      ,
      • Vinknes K.J.
      • Elshorbagy A.K.
      • Nurk E.
      • Drevon C.A.
      • Gjesdal C.G.
      • Tell G.S.
      • Nygard O.
      • Vollset S.E.
      • Refsum H.
      Plasma stearoyl-CoA desaturase indices: association with lifestyle, diet, and body composition.
      ). There is a competition for the desaturation of n-3 and n-6 PUFAs, resulting in probably differential association with obesity depending on n-6 and n-3 levels (
      • Schmitz G.
      • Ecker J.
      The opposing effects of n-3 and n-6 fatty acids.
      ). Overall, there is a dearth of information regarding the association between FA biomarkers, endogenous FA synthesis, and obesity.
      The aim of this study was to determine the association between S-PLFA percentages as biomarkers of dietary exposure and endogenous FA metabolism and indicators of obesity in a population of Mexican women. The novelty of this study relies on the wide range of FAs measured in serum phospholipids as biomarkers of dietary FAs and their endogenous metabolism.

      MATERIALS AND METHODS

       Study population

      The population study was comprised of a subgroup of women enrolled as controls (non-cancer cases) in a population-based case-control study on breast cancer conducted in Mexican women from 2004 to 2007, as previously described (
      • Angeles-Llerenas A.
      • Ortega-Olvera C.
      • Perez-Rodriguez E.
      • Esparza-Cano J.P.
      • Lazcano-Ponce E.
      • Romieu I.
      • Torres-Mejia G.
      Moderate physical activity and breast cancer risk: the effect of menopausal status.
      ). Briefly, participants in the current study were recruited from Mexico City, Monterrey, and Veracruz and matched to newly diagnosed breast cancer patients on the basis of age, region, and healthcare provider.

       Questionnaires

      An individual questionnaire was completed for each participant at the recruitment. The questionnaire contained information on the participant's socio-economic and demographic status, education history, self-reported personal and family morbidity (e.g., diabetes, hypertension, and arthritis), reproductive factors (gynecological history, menorrhea, contraception, and pregnancy), physical activity, smoking status, and dietary consumption.
      Menopausal status was defined according to the halting of the amenorrhea for 12 consecutive months, at least. In contrast to premenopausal women, postmenopausal women were those with natural menopause (over 12 months cessation of menstruation) and those with surgical menopause, who reported bilateral oophorectomy or those who did not know the type of surgery, but were over 48 years, given that mean age at menopause in Mexican women is 48 years (
      • Salazar-Martinez E.
      • Lazcano-Ponce E.C.
      • Gonzalez Lira-Lira G.
      • Escudero-De los Rios P.
      • Salmeron-Castro J.
      • Hernandez-Avila M.
      Reproductive factors of ovarian and endometrial cancer risk in a high fertility population in Mexico.
      ). Age at first menses and menarche were also collected.
      Physical activity was assessed considering the duration (minutes), the motive (occupation, exercise, leisure), the time (morning, evening, night), and the intensity (light, moderate, and vigorous) of the activities executed (e.g., walking, gardening, writing, watching television, reading a book, karate, etc.) and was reported in total metabolic equivalent of task (MET) hours per week. Smoking status considered self-reported current, never, or former smoking status.
      Energy intake was determined from a dietary food frequency questionnaire of 12 months previously validated in the Mexican population (
      • Hernández-Avila M.
      • Romieu I.
      • Parra S.
      • Hernandez-Avila J.
      • Madrigal H.
      • Willett W.
      Validity and reproducibility of a food frequency questionnaire to assess dietary intake of women living in Mexico City.
      ). Alcohol intake was computed from alcohol type consumed, as well as frequency of the consumption provided in the food frequency questionnaire.

       Anthropometry

      Anthropometric indicators were measured by trained field workers using standardized international recommendations (

      Lohman, T., A. Roche, and R. Martorell, . 1988. Anthropometric Standardization Reference Manual. Human Kinetics Books, Cham­paign, IL.

      ). Weight (kilograms) and height (centimeters) were measured using, respectively, an electronic scale and a stadiometer, with the women lightly dressed, barefoot, and in the orthostatic position. Waist (centimeters) and hip (centimeters) circumferences were measured with the woman in the standing position using a graduated, nonextensible tape, held not constricting, parallel to the floor, at the midpoint between the lowest rib and the iliac crest for the waist, and at the prominent part of the buttocks for the hip. BMI (weight/height squared, kilograms per square meter) and waist-to-hip ratio (WHR; waist/hip) were calculated using these measurements. BMI categories for underweight, normal or healthy weight, overweight, obesity, and morbid obesity were respectively <18.5 kg/m2, 18.5–24.9 kg/m2, 25–29.9 kg/m2, 30–39.9 kg/m2, and from and above 40 kg/m2.
      Body silhouettes were recalled as subjective measurements using a pictographic chart composed of six women corpulence drawings at incremental sizes hypothetically from leanness to morbid obesity (1, underweight; 2 and 3, normal weight; 4, overweight; 5, obesity; 6, morbid obesity) (
      • Stunkard A.J.
      • Sorensen T.
      • Schulsinger F.
      Use of the Danish Adoption Register for the study of obesity and thinness.
      ). Participants were asked to select the silhouette they most closely resembled during childhood (6–11 years), adolescence (12–18 years), early adulthood (18–20 years), later adulthood (25–35 years), and at the time of enrolment in the study.

       Ethical clearance

      Study participants provided written informed consent to participate in the study. Ethical approval was obtained from the Institutional Review Board of the Mexican National Institute of Public Health and from each of the participating hospitals.

       Analysis of S-PLFA

      Fasting blood samples were collected by venepuncture at recruitment, centrifuged, aliquoted and stored at −80°C. S-PLFA concentration was measured using the lipidomic gas chromatography platform at the International Agency for Research on Cancer (Lyon, France). The methodology allows the separation and quantification of 60 FAs, including 15 TFA isomers from industrial processing and natural animal sources in a 1 h run.
      Briefly, total lipids were extracted from serum samples (200 μl) with chloroform-methanol 2:1 (v/v) containing antioxidant butylated hydroxytoluene and L-A-phosphatidylcholine-dimyristoyl-d54 as an internal standard. Phospholipids were purified by adsorption chromatography. FA methyl esters (FAMEs) were formed by transmethylation with Methyl-Prep II (Alltech, Deerfield, IL). Analyses were carried out on the gas chromatograph 7890A (Agilent Technologies, Santa Clara, CA). Select for FAME capillary columns (Agilent Technologies), which have the specificity to discriminate TFAs from cis FAs, were used for separation of FAMEs. Each FA was identified with purchased standards, which were injected in the gas chromatograph to determine their retention time.
      The relative levels of each FA, expressed as percent of total FAs, were quantified by integrating the area under the peak and dividing the result by the total area. Coefficients of variation for FAs ranged from 1.81% for large peaks (peak >1% of total FAs) to 9.75% for the smallest peaks (peak <1% of total FAs). Using values for 60 individual FAs, we calculated the percentage of the following groups: SFAs, cis-MUFAs, ruminant TFAs, ITFAs, which are TFA isomers obtained during the industrial processing of vegetal fats by heating, refining, or hydrogenation, cis-n-6 PUFAs, long-chain n-6 PUFAs, n-3 PUFAs, and long-chain n-3 PUFAs. We calculated the ratio of long-chain n-6/long-chain n-3 PUFAs. We also determined the desaturation indices as the ratio of product to substrate, either oleic acid to stearic acid (SCD-18) or the ratio of palmitoleic acid to palmitic acid (SCD-16), as biomarkers of stearoyl-CoA desaturase activity (
      • Chajès V.
      • Joulin V.
      • Clavel-Chapelon F.
      The fatty acid desaturation index of blood lipids, as a biomarker of hepatic stearoyl-CoA desaturase expression, is a predictive factor of breast cancer risk.
      ). In addition, the activity of FADSs, FADS1 and FADS2, were determined by the ratio of 20:4n-6 [arachidonic acid (AA)] to 20:3n-6 [dihomo-γ-linolenic acid (DGLA)] and 22:6n-3 (DHA) to 22:5n-3 [docosapentaenoic acid (DPA)], respectively.

       Statistical analyses

      FAs expressed as the percentage of total FAs were used for the statistical analysis. Frequencies were presented for the categorical variables, while means and SDs were presented for all the continuous variables. FA values were log-transformed and geometric means with 95% CI were reported for the analysis.
      Multiple linear regressions using the FAs or the desaturation indices as dependent variables and obesity indicators (BMI, waist, WHR) as independent variables were performed. Prior to the regression analysis, FA levels were Z-standardized for better comparison. Regression adjustments were performed for age (continuous variable), menopausal status (pre- and postmenopause), physical activity (total MET in minutes per week), smoking status (nonsmokers, current smokers, exsmokers), education (none, incomplete primary, complete primary, complete secondary, com­plete high school), alcohol consumption (grams per day), energy intake (kilocalories per day), and analytical batch. The coefficient (β), the SE, and the P value of the multiple regressions were reported. Due to the number of tests performed, q-values were calculated by transforming the P values for multiple comparisons using the false discovery rate via the Benjamini-Hochberg procedure (
      • Benjamini Y.
      • Hochberg Y.
      Controlling the false discovery rate: a practical and powerful approach to multiple testing.
      ). Statistical analyses were performed using STATA version 14.1 (StataCorp, College Station, TX) and R (R Foundation for Statistical Computing version 3.0.2, Vienna, Austria).

      RESULTS

      The general characteristics of the study population are presented in Table 1. A total of 372 women with an average age of 50.1 years at the time of recruitment were included in the study. The prevalence of overweight and obesity in the population study were respectively 43.0% and 45.7% with a mean BMI of 30.3 kg/m2. Median silhouette shape increased throughout life course from level 1 at childhood to reach level 4 at adulthood (P = 0.011), showing an evolution from leanness to obesity with age in the study population.
      TABLE 1General characteristics of the study population
      VariablesMean ± SD or Frequency (%)
      Age, years50.1 ± 9.5
      Weight, kg69.9 ± 13.5
      Height, cm151.8 ± 6.0
      BMI, kg/m230.3 ± 5.2
      Waist, cm98.2 ± 12.6
      Hip, cm108.2 ± 11.3
      WHR0.91 ± 0.06
      Age at first menarche, years12.9 ± 1.6
      Age at menopause, years48.3 ± 5.8
      Physical activity, total MET min/week276.3 ± 47.1
      Alcohol intake, g/week5.1 ± 29.7
      Energy intake, kcal/day1,921.6 ± 705.3
      Menopause, %174 (46.8)
      Smokers, %108 (29.0)
      Diabetes, %51 (13.7)
      Education, %
      None28 (7.5)
      Incomplete primary92 (24.7)
      Complete primary119 (32.0)
      Complete secondary100 (26.9)
      Complete high school17 (4.6)
      College or graduate education16 (4.3)
      Silhouette at childhood (6–11 years)
      1
      Median value.
      206 (55.4)
      2101 (27.2)
      350 (13.4)
      410 (2.7)
      55 (1.3)
      60
      Silhouette at adolescence (12–18 years)
      1138 (37.1)
      2
      Median value.
      145 (39.0)
      367 (18.0)
      415 (4.0)
      55 (1.3)
      62 (0.5)
      Silhouette at early adulthood (18–20 years)
      167 (18.0)
      2
      Median value.
      156 (41.9)
      3115 (30.9)
      425 (6.7)
      55 (1.3)
      64 (1.1)
      Silhouette at adulthood (25–35 years)
      115 (4.0)
      294 (25.3)
      3
      Median value.
      145 (39.1)
      490 (24.3)
      524 (6.5)
      63 (0.8)
      Silhouette actual (at the time of the recruitment)
      16 (1.6)
      235 (9.4)
      388 (23.7)
      4
      Median value.
      149 (40.2)
      562 (16.7)
      631 (8.4)
      Missing values: one for silhouette at adulthood and actual silhouette; four for weight, height, BMI, and waist; five for hip and WHR; 15 for alcohol consumption.
      a Median value.
      The S-PLFA profile of the population is indicated in Table 2. Individual FAs are grouped by family (saturates, monounsaturates, n-6 and n-3 polyunsaturates) and by conformation (trans and cis). The relative amount (percent of total FAs) of groups (SFAs, MUFAs, ruminant TFAs, ITFAs, n-3 and n-6 PUFAs) and the n-6/n-3 PUFA ratio were provided. Desaturation indices, SCD-16, SCD-18, FADS1, and FADS2, used as biomarkers of FA metabolism were also provided. Palmitic acid (16:0) and linoleic acid (18:2n-6) were the most abundant S-PLFAs, accounting for the high percentages of total SFAs and n-6 PUFAs. Compared with n-6 PUFAs, n-3 PUFA percentages were lower and this was reflected in an n-6/n-3 PUFA ratio of 8.2. ITFAs represented 1.4% of total S-PLFAs.
      TABLE 2Geometric means of S-PLFAs and desaturation indices in the study population
      Mean (95% CI)
      SFAs
      14:0 (myristic acid)0.20 (0.19–0.21)
      15:0 (pentadecanoic acid)0.14 (0.13–0.14)
      16:0 (palmitic acid)23.8 (23.6–24.1)
      17:0 (heptadecanoic acid)0.38 (0.38–0.39)
      18:0 (stearic acid)14.7 (14.5–14.9)
      MUFAs
      cis-MUFA
      16:1n-7 (palmitoleic acid)0.68 (0.66–0.70)
      18:1n-50.21 (0.20–0.22)
      18:1n-7 (cis-vaccenic acid)1.48 (1.45–1.50)
      18:1n-9 (oleic acid)10.2 (10.1–0.4)
      trans-MUFA
      16:1n-7/9 (palmitelaidic acid)0.58 (0.55–0.61)
      18:1n-9/12 (elaidic acid)0.51 (0.49–0.53)
      18:1n-7 (vaccenic acid)0.18 (0.17–0.19)
      PUFAs
      cis-n-6 PUFA
      18:2n-6 (linoleic acid)24.0 (23.7–24.3)
      18:3n-6 (γ-linolenic acid)0.10 (0.09–0.10)
      20:3n-6 (DGLA)3.95 (3.86–4.04)
      20:4n-6 (AA)10.4 (10.2–10.6)
      22:4n-6 (adrenic acid)0.50 (0.49–0.51)
      22:5n-6 (osbond acid)0.45 (0.44–0.46)
      trans-n-6 PUFA
      Conjugated linoleic acid0.19 (0.18–0.19)
      18:2ct, 18:2tc, 18:2tt (trans linoleic acid)0.16 (0.15–0.16)
      cis-n-9 PUFA
      20:3n-9 (mead acid)0.12 (0.12–0.13)
      cis-n-3 PUFA
      18:3n-3ccc (α-linolenic acid)0.27 (0.26–0.28)
      20:5n-3 (EPA)0.46 (0.44–0.48)
      22:5n-3 (DPA)0.93 (0.91–0.95)
      22:6n-3 (DHA)3.10 (3.03–3.17)
      trans-n-3 PUFA
      18:3n-3cct, ctt, ttt (trans α-linolenic acid)0.07 (0.07–0.08)
      Groupings
      Total SFAs39.5 (39.2–39.8)
      Total cis-MUFAs13.0 (12.8–13.1)
      Total trans ruminant FAs0.39 (0.38–0.41)
      Total ITFAs1.39 (1.35–1.43)
      Total cis-n-6 PUFAs40.3 (40.0–40.6)
      Total long-chain n-6 PUFAs16.0 (15.8–16.2)
      Total cis-n-3 PUFAs4.91 (4.82–5.01)
      Total long-chain n-3 PUFAs4.63 (4.53–4.72)
      Ratio PUFA n-6/n-38.19 (8.03–8.36)
      Desaturation indexes
      SCD-16 (16:1n-7cis/16:0)0.03 (0.027–0.029)
      SCD-18 (18:1n-9cis/18:0)0.70 (0.68–0.71)
      FADS1 (20:4n-6/20:3n-6)2.63 (2.55–2.71)
      FADS2 (DHA/EPA)6.72 (6.40–7.06)
      FA values are expressed as percentage of total FAs. The values provided are geometric means with 95% CI.
      Table 3 shows the multiple regressions for the association between individual FAs and subgroups, and BMI, waist circumference, and WHR. Prior to control for multiple testing, BMI was positively associated with stearic acid (β = 0.024, P = 0.007), palmitoleic acid (β = 0.031, P = 0.001), DGLA (β = 0.043, P = 0.000), and EPA (β = 0.025, P = 0.020), and negatively associated with heptadecanoic acid (β = −0.026, P = 0.009) and cis-vaccenic acid (β = −0.027, P = 0.007). When the associations were corrected for multiple testing, q-values remained significant for palmitoleic acid (q = 0.014) and DGLA (q = 0.0002). Similar results were obtained for waist circumference. In contrast, the odd-chain FAs, pentadecanoic acid (β = −1.733, P = 0.012, q = 0.079) and heptadecanoic acid (β = −3.778, P = 0.000, q = 0.0002), tended to be negatively associated with WHR, while n-6 PUFAs (β = 1.497, P = 0.047, q = 0.22) and the n-6/n-3 PUFA ratio (β = 1.654, P = 0.040, q = 0.19) showed a positive trend with WHR. Finally, we did not observe a significant positive trend between ITFAs and obesity.
      TABLE 3Multiple regression models for the association between S-PLFAs and obesity indicators
      BMIWaist CircumferenceWHR
      β
      FA values were log-transformed and Z-standardized for the analysis for better comparison. All the regression models were adjusted for age, alcohol consumption, smoking, energy intake, education, physical activity, menopause, and batch of analysis. P or q values < 0.05 are shown in boldface type.
      SEPqβ
      FA values were log-transformed and Z-standardized for the analysis for better comparison. All the regression models were adjusted for age, alcohol consumption, smoking, energy intake, education, physical activity, menopause, and batch of analysis. P or q values < 0.05 are shown in boldface type.
      SEPqβ
      FA values were log-transformed and Z-standardized for the analysis for better comparison. All the regression models were adjusted for age, alcohol consumption, smoking, energy intake, education, physical activity, menopause, and batch of analysis. P or q values < 0.05 are shown in boldface type.
      SEPq
      SFAs
      14:0 (myristic acid)0.0080.0080.310.700.0040.0030.210.551.2370.6300.0510.22
      15:0 (pentadecanoic acid)0.0010.0090.930.98−0.0050.0040.160.47−1.7330.6840.0120.079
      16:0 (palmitic acid)0.0040.0070.560.870.0010.0030.680.950.3520.5650.530.86
      17:0 (heptadecanoic acid)−0.0260.0100.0090.065−0.0170.0040.0000.0002−3.7780.7760.0000.0002
      18:0 (stearic acid)0.0240.0090.0070.0580.0050.0040.190.52−0.9260.7010.190.52
      MUFAs
      cis-MUFAs
      16:1n-7 (palmitoleic acid)0.0310.0100.0010.0140.0120.0040.0030.0331.2200.7690.110.39
      18:1n-5−0.0050.0100.600.89−0.0020.0040.670.95−0.9670.7900.220.56
      18:1n-7 (cis-vaccenic acid)−0.0270.0100.0070.058−0.0100.0040.0120.079−1.8960.7870.0170.11
      18:1n-9 (oleic acid)−0.0180.0100.0690.27−0.0080.0040.0520.22−0.4570.7660.550.87
      trans-MUFAs
      16:1n-7/9 (palmitelaidic acid)0.0050.0100.540.860.0010.0030.790.97−0.1340.6050.820.97
      18:1n-9/12 (elaidic acid)−0.0130.0100.210.55−0.0030.0040.490.85−0.4050.7980.610.90
      18:1n-7 (vaccenic acid)−0.0100.0080.340.71−0.0030.0030.350.71−0.8970.6520.170.48
      PUFAs
      cis-n-6 PUFAs
      18:2n-6 (linoleic acid)−0.0070.0100.470.840.0030.0040.410.761.540.7990.0550.23
      18:3n-6 (γ-linolenic acid)0.0270.0100.0090.0650.0040.0040.360.720.0140.8110.990.99
      20:3n-6 (DGLA)0.0430.0100.0000.00020.0130.0040.0020.0230.6240.8050.440.79
      20:4n-6 (AA)−0.0070.0100.520.86−0.0040.0040.290.69−0.5500.8100.500.86
      22:4n-6 (adrenic acid)−0.0070.0100.490.85−0.0030.0040.510.860.9520.8000.230.58
      22:5n-6 (osbond acid)−0.0290.0100.0060.053−0.0100.0040.0190.120.8010.8230.330.71
      trans-n-6 PUFAs
      Conjugated linoleic acid0.0140.0100.160.470.0060.0040.130.420.3300.7910.680.95
      18:2ct, 18:2tc, 18:2tt (trans linoleic acid)0.0010.0090.920.980.0020.0040.600.890.1910.6850.780.97
      cis-n-9 PUFAs
      20:3n-9 (mead acid)0.0110.0100.290.690.0010.0040.780.97−0.0680.7960.930.98
      cis-n-3 PUFAs
      18:3n-3ccc (α-linolenic acid)−0.0050.0110.610.90−0.0010.0040.740.97−0.2830.8470.740.97
      20:5n-3 (EPA)0.0250.0100.0200.120.0070.0040.120.40−0.4610.820.570.87
      22:5n-3 (DPA)−0.0050.0100.590.89−0.0010.0040.880.970.0130.7810.990.99
      22:6n-3 (DHA)−0.0090.0100.370.74−0.0060.0040.170.48−1.3120.7920.0980.35
      trans-n-3 PUFAs
      18:3n-3cct, ctt, ttt (trans α-linolenic acid)0.0010.0100.940.980.0030.0040.530.860.7950.8290.340.71
      Groupings
      Total SFAs0.0180.0090.0510.220.0030.0040.380.74−0.4290.7080.540.86
      Total cis-MUFAs−0.0170.0100.070.27−0.0070.0040.0570.24−0.6330.7570.400.76
      Total trans ruminant FAs−0.0020.0090.830.97−0.0010.0040.730.97−0.7340.7100.300.70
      Total ITFAs−0.0040.0100.670.95−0.0010.0040.840.97−0.2310.7290.750.97
      Total cis-n-6 PUFAs−0.0020.0100.860.970.0040.0040.310.701.4970.7520.0470.22
      Total long-chain n-6 PUFAs0.0080.0100.410.760.0010.0040.890.97−0.1130.7810.880.97
      Total cis-n-3 PUFAs−0.0020.0100.800.97−0.0030.0040.490.85−1.1290.7840.150.47
      Total long-chain n-3 PUFAs−0.0020.0100.870.97−0.0020.0040.530.86−1.0800.7830.170.48
      Ratio PUFA n-6/n-30.0020.0100.860.970.0040.0040.310.701.6540.8030.0400.19
      a FA values were log-transformed and Z-standardized for the analysis for better comparison. All the regression models were adjusted for age, alcohol consumption, smoking, energy intake, education, physical activity, menopause, and batch of analysis. P or q values < 0.05 are shown in boldface type.
      We investigated to determine whether the association between the indicators of obesity and some specific FAs might be influenced by their inter-relationship with other FAs. Figure 1 shows matrices correlation between the individual FAs, the groupings, and the desaturation indices (color matrix without numeral). SCD-16 showed strong correlation with most of the FAs associated with the obesity indicators, heptadecanoic acid (r = −0.361, P = 0.000), stearic acid (r = −0.280, P = 0.000), cis-vaccenic acid (r = 0.165, P = 0.002), γ-linolenic acid (r = 0.517, P = 0.000), DGLA (r = 0.457, P = 0.000), EPA (r = 0.114, P = 0.028), and n-6 PUFAs (r = −0.174, P = 0.001). We wanted to investigate whether the associations between S-PLFAs and obesity indicators were influenced by the endogenous activity proxied through SCD-16. When further adjusted for SCD-16 (supplementary Table S1), similar associations remained with the few exceptions of total MUFAs, which showed negative association with BMI and waist circumference (both P and q-values <0.001), among others.
      Figure thumbnail gr1
      Fig. 1Correlation matrix between the FAs. Correlations between FAs are represented by color squares, bluish for negative correlations, reddish for positive correlations, and yellowish for no or weak correlations. Rows and columns are reordered in clades according to a hierarchical clustering method based on the Euclidean distance. FAs were organized in two major clades, the first including mostly cis-n-3 PUFAs, trans ruminant and industrial FAs, and desaturation indices, FADS1 and FADS2, while the second clade includes cis-MUFAs, SFAs, and desaturation indices, SCD-16 and SCD-18. FAs of the same group are positively correlated with each other, probably due to similar dietary sources. SCD-16 was significantly correlated to most of the FAs associated with BMI, waist circumference, and WHR.
      Table 4 presents the multiple regressions between desaturation indices and BMI, waist circumference, and WHR. Before correction, all the desaturation indices were significantly associated with BMI and waist circumference, but not with WHR. The associations remained significant and positive for SCD-16 (for BMI, β = 0.034, P = 0.001, q = 0.014; and for waist circumference, β = 0.013, P = 0.002, q = 0.023) and negative for FADS1 (for BMI, β = −0.036, P = 0.001, q = 0.014; and for waist circumference, β = −0.012, P = 0.005, q = 0.048) after adjustment for multiple testing.
      TABLE 4Multiple regression models for the association between the desaturation indices and obesity indicators in the study population
      BMIWaist CircumferenceWHR
      β
      Desaturation index values were log-transformed and Z-standardized for the analysis for better comparison. All the regression models were adjusted for age, alcohol consumption, smoking, energy intake, education, physical activity, menopause, and batch of analysis. P or q values < 0.05 are shown in boldface type.
      SEPqβ
      Desaturation index values were log-transformed and Z-standardized for the analysis for better comparison. All the regression models were adjusted for age, alcohol consumption, smoking, energy intake, education, physical activity, menopause, and batch of analysis. P or q values < 0.05 are shown in boldface type.
      SEPqβ
      Desaturation index values were log-transformed and Z-standardized for the analysis for better comparison. All the regression models were adjusted for age, alcohol consumption, smoking, energy intake, education, physical activity, menopause, and batch of analysis. P or q values < 0.05 are shown in boldface type.
      SEPq
      Desaturation index 16 (16:1n-7cis/16:0)0.0340.0100.0010.0140.0130.0040.0020.0231.2260.7910.120.40
      Desaturation index 18 (18:1n-9cis/18:0)−0.0240.0090.0090.065−0.0070.0040.0520.220.2430.7220.740.97
      FADS1 (20:4n-6/20:3n-6)−0.0360.0100.0010.014−0.0120.0040.0050.048−0.8040.8330.340.71
      FADS2 (DHA/EPA)−0.0290.0100.0060.053−0.0090.0040.0320.16−0.1750.8260.830.97
      a Desaturation index values were log-transformed and Z-standardized for the analysis for better comparison. All the regression models were adjusted for age, alcohol consumption, smoking, energy intake, education, physical activity, menopause, and batch of analysis. P or q values < 0.05 are shown in boldface type.

      DISCUSSION

      This is the first epidemiologic study to report the association between S-PLFA levels and the indicators of obesity in a population of Mexican women. We found that desaturation index, SCD-16, as a marker of endogenous synthesis of monounsaturated palmitoleic acid, was positively associated with BMI and waist circumference. In contrast, SCD-18, FADS1, and FADS2 were negatively associated with BMI and waist circumference. Regarding individual FAs, BMI and waist were negatively associated with heptadecanoic acid and positively associated with EPA and DGLA. WHR was positively associated with the n-6/n-3 PUFA ratio. These findings suggest that specific classes of FAs may be involved in the etiology of obesity and underscore the importance of measuring FA biomarkers for furthering understanding of the role of dietary FAs and metabolism in obesity.
      Few epidemiological studies have investigated the relation between individual FAs, desaturation indices, and adiposity. Available epidemiological studies have reported a positive association between palmitoleic acid, DGLA, TFAs and SFAs, SCD16, and indicators of obesity. However, these studies have applied discrepant methodological approaches using, variably, body weight change (
      • Chajès V.
      • Biessy C.
      • Ferrari P.
      • Romieu I.
      • Freisling H.
      • Huybrechts I.
      • Scalbert A.
      • Bueno de Mesquita B.
      • Romaguera D.
      • Gunter M.J.
      Plasma elaidic acid level as biomarker of industrial trans fatty acids and risk of weight change: report from the EPIC Study.
      ), BMI (
      • Vinknes K.J.
      • Elshorbagy A.K.
      • Nurk E.
      • Drevon C.A.
      • Gjesdal C.G.
      • Tell G.S.
      • Nygard O.
      • Vollset S.E.
      • Refsum H.
      Plasma stearoyl-CoA desaturase indices: association with lifestyle, diet, and body composition.
      ,
      • Smit L.A.
      • Willett W.C.
      • Campos H.
      trans-fatty acid isomers in adipose tissue have divergent associations with adiposity in humans.
      ,
      • Murakami K.
      • Sasaki S.
      • Takahashi Y.
      • Uenishi K.
      • Watanabe T.
      • Kohri T.
      • Yamasaki M.
      • Watanabe R.
      • Baba K.
      • Shibata K.
      Lower estimates of delta-5 desaturase and elongase activity are related to adverse profiles for several metabolic risk factors in young Japanese women.
      ), waist circumference (
      • Micallef M.
      • Munro I.
      • Phang M.
      • Garg M.
      Plasma n-3 polyunsaturated fatty acids are negatively associated with obesity.
      ), WHR (
      • Das M.
      • Pal S.
      • Ghosh A.
      Association of metabolic syndrome with obesity measures, metabolic profiles, and intake of dietary fatty acids in people of Asian Indian origin.
      ), and body fatness (
      • Vinknes K.J.
      • Elshorbagy A.K.
      • Nurk E.
      • Drevon C.A.
      • Gjesdal C.G.
      • Tell G.S.
      • Nygard O.
      • Vollset S.E.
      • Refsum H.
      Plasma stearoyl-CoA desaturase indices: association with lifestyle, diet, and body composition.
      ,
      • Smit L.A.
      • Willett W.C.
      • Campos H.
      trans-fatty acid isomers in adipose tissue have divergent associations with adiposity in humans.
      ) as obesity indicators, and as biomarkers of FAs, S-PLFAs (or plasma) (
      • Chajès V.
      • Biessy C.
      • Ferrari P.
      • Romieu I.
      • Freisling H.
      • Huybrechts I.
      • Scalbert A.
      • Bueno de Mesquita B.
      • Romaguera D.
      • Gunter M.J.
      Plasma elaidic acid level as biomarker of industrial trans fatty acids and risk of weight change: report from the EPIC Study.
      ), whole-blood or erythrocyte FAs (
      • Sansone A.
      • Tolika E.
      • Louka M.
      • Sunda V.
      • Deplano S.
      • Melchiorre M.
      • Anagnostopoulos D.
      • Chatgilialoglu C.
      • Formisano C.
      • Di Micco R.
      Hexadecenoic fatty acid isomers in human blood lipids and their relevance for the interpretation of lipidomic profiles.
      ), and adipose tissue FAs (
      • Smit L.A.
      • Willett W.C.
      • Campos H.
      trans-fatty acid isomers in adipose tissue have divergent associations with adiposity in humans.
      ), which limit the comparison between studies. In parallel, other studies have assessed dietary intake of FA classes (
      • Thompson A.K.
      • Minihane A.M.
      • Williams C.M.
      Trans fatty acids and weight gain.
      ), an approach shown to be prone to measurement errors.
      In comparison with the European EPIC study for which S-PLFAs are available in a large sample of the population through the same methodology (
      • Saadatian-Elahi M.
      • Slimani N.
      • Chajes V.
      • Jenab M.
      • Goudable J.
      • Biessy C.
      • Ferrari P.
      • Byrnes G.
      • Autier P.
      • Peeters P.H.
      Plasma phospholipid fatty acid profiles and their association with food intakes: results from a cross-sectional study within the European Prospective Investigation into Cancer and Nutrition.
      ), S-PLFA composition in this population of Mexican women was mainly characterized by low levels of n-3 PUFAs and suitably four times higher n-6/n-3 PUFA ratio. This imbalanced n-6/n-3 ratio is in agreement with a study reporting an estimated dietary n-6/n-3 ratio of 16.3 in a nationally representative study in the Mexican population (
      • Ramírez-Silva I.
      • Villalpando S.
      • Moreno-Saracho J.E.
      • Bernal-Medina D.
      Fatty acids intake in the Mexican population. Results of the National Nutrition Survey 2006.
      ), while a ratio of one to four is recommended (
      • Simopoulos A.P.
      The importance of the ratio of omega-6/omega-3 essential fatty acids.
      ). Second, percentages of ITFAs were more than double in Mexican women compared with EPIC participants (
      • Saadatian-Elahi M.
      • Slimani N.
      • Chajes V.
      • Jenab M.
      • Goudable J.
      • Biessy C.
      • Ferrari P.
      • Byrnes G.
      • Autier P.
      • Peeters P.H.
      Plasma phospholipid fatty acid profiles and their association with food intakes: results from a cross-sectional study within the European Prospective Investigation into Cancer and Nutrition.
      ).
      This latter observation is of concern, as industrially produced TFAs from partially hydrogenated vegetable oils induce changes in circulating lipid content, alterations in metabolic and signaling pathways, systemic inflammation, endothelial dysfunction, and insulin resistance and contribute to higher the risk of coronary heart disease and cardiovascular disease (
      • Mozaffarian D.
      • Aro A.
      • Willett W.C.
      Health effects of trans-fatty acids: experimental and observational evidence.
      ). Regarding obesity, animal studies reported slight weight gain and abdominal obesity with increasing intake of ITFAs (
      • Kavanagh K.
      • Jones K.L.
      • Sawyer J.
      • Kelley K.
      • Carr J.J.
      • Wagner J.D.
      • Rudel L.L.
      Trans fat diet induces abdominal obesity and changes in insulin sensitivity in monkeys.
      ,
      • Dorfman S.E.
      • Laurent D.
      • Gounarides J.S.
      • Li X.
      • Mullarkey T.L.
      • Rocheford E.C.
      • Sari-Sarraf F.
      • Hirsch E.A.
      • Hughes T.E.
      • Commerford S.R.
      Metabolic implications of dietary trans-fatty acids.
      ), whereas the findings are not supported by epidemiological studies (
      • Thompson A.K.
      • Minihane A.M.
      • Williams C.M.
      Trans fatty acids and weight gain.
      ). In the present study, we also failed to report a significant positive association between ITFAs and indicators of obesity. The cross-sectional design of our study might explain the lack of an association between biomarkers of TFAs and obesity indicators. Indeed, a prospective evaluation of plasma phospholipid FAs and weight gain in Europe showed a positive association between baseline plasma levels of ITFAs and weight gain in women (
      • Chajès V.
      • Biessy C.
      • Ferrari P.
      • Romieu I.
      • Freisling H.
      • Huybrechts I.
      • Scalbert A.
      • Bueno de Mesquita B.
      • Romaguera D.
      • Gunter M.J.
      Plasma elaidic acid level as biomarker of industrial trans fatty acids and risk of weight change: report from the EPIC Study.
      ). In addition, the present study population is quite homogenous with respect to BMI and TFA range contents. Additional prospective epidemiological studies are needed to evaluate the relation between individual and total TFAs and obesity in populations with a wider range of BMI and TFA consumption.
      Our findings suggest a significant relation between increased endogenous palmitoleic acid synthesis and obesity. While it is not possible in the present cross-sectional design to conclude on any causal relationship between SCD-16 and obesity, numerous epidemiological studies have also previously reported a positive association between obesity and SCD-16 in women, irrespective of their age (
      • Vinknes K.J.
      • Elshorbagy A.K.
      • Nurk E.
      • Drevon C.A.
      • Gjesdal C.G.
      • Tell G.S.
      • Nygard O.
      • Vollset S.E.
      • Refsum H.
      Plasma stearoyl-CoA desaturase indices: association with lifestyle, diet, and body composition.
      ,
      • Murakami K.
      • Sasaki S.
      • Takahashi Y.
      • Uenishi K.
      • Watanabe T.
      • Kohri T.
      • Yamasaki M.
      • Watanabe R.
      • Baba K.
      • Shibata K.
      Lower estimates of delta-5 desaturase and elongase activity are related to adverse profiles for several metabolic risk factors in young Japanese women.
      ). At a physiological level, the SCD activity is used by the body to convert SFAs to MUFAs to prevent the intracellular accumulation of SFAs susceptible to initiate lipoapoptosis, especially palmitate-induced apoptosis (
      • Collins J.M.
      • Neville M.J.
      • Hoppa M.B.
      • Frayn K.N.
      De novo lipogenesis and stearoyl-CoA desaturase are coordinately regulated in the human adipocyte and protect against palmitate-induced cell injury.
      ). An increased desaturation index measured in plasma phospholipids has been associated with metabolic disorders related to obesity, including insulin resistance, diabetes, cardiovascular diseases, inflammation, metabolic syndrome, and breast cancer (
      • Chajès V.
      • Joulin V.
      • Clavel-Chapelon F.
      The fatty acid desaturation index of blood lipids, as a biomarker of hepatic stearoyl-CoA desaturase expression, is a predictive factor of breast cancer risk.
      ).
      In agreement with previous studies (
      • Warensjö E.
      • Rosell M.
      • Hellenius M.L.
      • Vessby B.
      • De Faire U.
      • Riserus U.
      Associations between estimated fatty acid desaturase activities in serum lipids and adipose tissue in humans: links to obesity and insulin resistance.
      ), we found dissimilar association with obesity for SCD-16 and SCD-18, which are both expressions of SCD-1 activity. In a cross-sectional study, measurement of SCD-1 activity in liver samples showed that SCD-16 better reflects the expression of hepatic SCD-1 than SCD-18 (
      • Peter A.
      • Cegan A.
      • Wagner S.
      • Lehmann R.
      • Stefan N.
      • Konigsrainer A.
      • Konigsrainer I.
      • Haring H.U.
      • Schleicher E.
      Hepatic lipid composition and stearoyl-coenzyme A desaturase 1 mRNA expression can be estimated from plasma VLDL fatty acid ratios.
      ). In fact, in contrast to oleic acid, palmitoleic acid in the diet is low. Therefore, the ratio 18:1n-9/18:0 is susceptible to encompass a large dietary component compared with 16:1n-7/16:0, largely supported by body cell synthesis (
      • Warensjö E.
      • Riserus U.
      • Gustafsson I.B.
      • Mohsen R.
      • Cederholm T.
      • Vessby B.
      Effects of saturated and unsaturated fatty acids on estimated desaturase activities during a controlled dietary intervention.
      ), suggesting that SCD-16 is a more reliable marker of endogenous lipogenesis than SCD-18. Thus, the positive association between SCD-16 and BMI might reflect increased endogenous synthesis of palmitoleic acid, while the inverse association between SCD-18 and BMI might be related to a diet rich in vegetable oils rich in oleic acid.
      There is a dearth of evidence on how SCD-16, as a reflection of endogenous synthesis of palmitoleic acid, is affected by diet and hormones. In a controlled cross-over study, a high dietary intake of SFAs has been shown to increase the SCD-16 measured in blood cholesterol esters and phospholipids (
      • Warensjö E.
      • Riserus U.
      • Gustafsson I.B.
      • Mohsen R.
      • Cederholm T.
      • Vessby B.
      Effects of saturated and unsaturated fatty acids on estimated desaturase activities during a controlled dietary intervention.
      ). SCD-1 activity is also activated by high-carbohydrate diets, especially those enriched in rapidly absorbed refined carbohydrates, such as glucose and fructose (
      • Flowers M.T.
      • Ntambi J.M.
      Stearoyl-CoA desaturase and its relation to high-carbohydrate diets and obesity.
      ). As a consequence, the high SCD-16 in serum phospholipids that is positively associated with BMI in our population study may be the result of a diet rich in SFAs and carbohydrates, with concomitant increased hepatic desaturation of dietary palmitic to palmitoleic acid. Finally, insulin is an upregulator of SCD-16 activity (
      • Miyazaki M.
      • Ntambi J.M.
      Role of stearoyl-coenzyme A desaturase in lipid metabolism.
      ), suggesting that increased SCD-16 associated with increased BMI might reflect an underlying metabolic profile characterized by chronic hyperinsulinemia.
      Obesity is characterized by a series of alterations in phospholipid FA content and composition and their endogenous synthesis, resulting in greater susceptibility to inflammation. In obese subjects, serum short-chain MUFAs and SFAs are positively correlated to inflammatory markers and C-reactive protein, while odd-chain and iso-branched chain SFAs showed inverse association (
      • Mika A.
      • Sledzinski T.
      Alterations of specific lipid groups in serum of obese humans: a review.
      ). Eicosanoids are the products of n-3 and n-6 PUFAs, which include pro-inflammatory eicosanoid mediators from AA, whereas anti-inflammatory eicosanoid products are produced from the n-3 PUFAs (
      • Bagga D.
      • Wang L.
      • Farias-Eisner R.
      • Glaspy J.A.
      • Reddy S.T.
      Differential effects of prostaglandin derived from omega-6 and omega-3 polyunsaturated fatty acids on COX-2 expression and IL-6 secretion.
      ). Animal studies and in vitro studies indicated that EPA and DHA can hinder the production of an array of inflammatory cytokines, including TNFα, IL-1, IL-6, IL-8, and IL-12 (
      • Calder P.C.
      Mechanisms of action of (n-3) fatty acids.
      ). Likewise with inflammation, n-3 PUFAs are, in general, negatively associated with obesity (
      • Sansone A.
      • Tolika E.
      • Louka M.
      • Sunda V.
      • Deplano S.
      • Melchiorre M.
      • Anagnostopoulos D.
      • Chatgilialoglu C.
      • Formisano C.
      • Di Micco R.
      Hexadecenoic fatty acid isomers in human blood lipids and their relevance for the interpretation of lipidomic profiles.
      ). It is therefore intriguing that in our study, we found a positive association between EPA and BMI and waist circumference, despite few studies reporting similar findings (
      • Iso H.
      • Rexrode K.M.
      • Stampfer M.J.
      • Manson J.E.
      • Colditz G.A.
      • Speizer F.E.
      • Hennekens C.H.
      • Willett W.C.
      Intake of fish and omega-3 fatty acids and risk of stroke in women.
      ). However, serum content of EPA and other individual n-3 PUFAs depends on dietary intake, enzyme activity, and the competition in enzymatic conversion between n-6 and n-3. Therefore, the serum n-6/n-3 PUFA ratio, which considers the balance between the two families, might be more informative than individual PUFAs. We found a significant positive correlation between the n-6/n-3 PUFA ratio and WHR in our study. This ratio is exceedingly increased in typical Westernized diets, where it amounts to 20:1 and even more (
      • Simopoulos A.P.
      An increase in the omega-6/omega-3 fatty acid ratio increases the risk for obesity.
      ), and is positively associated with diverse chronic diseases, including atherosclerosis, obesity, diabetes, and breast cancer (
      • Simopoulos A.P.
      An increase in the omega-6/omega-3 fatty acid ratio increases the risk for obesity.
      ,
      • Yang B.
      • Ren X.L.
      • Fu Y.Q.
      • Gao J.L.
      • Li D.
      Ratio of n-3/n-6 PUFAs and risk of breast cancer: a meta-analysis of 274135 adult females from 11 independent prospective studies.
      ). Specifically regarding obesity, the mechanism involved in the obesogenicity of an imbalanced n-6/n-3 ratio is not fully elucidated, but Simopoulos (
      • Simopoulos A.P.
      An increase in the omega-6/omega-3 fatty acid ratio increases the risk for obesity.
      ) suggested multiple pathways involving adipogenesis, lipid homeostasis, appetite regulation, and, most importantly, systemic inflammation. Interestingly, Kaska et al. (
      • Kaska L.
      • Mika A.
      • Stepnowski P.
      • Proczko M.
      • Ratnicki-Sklucki K.
      • Sledzinski T.
      • Goyke E.
      • Swierczynski J.
      The relationship between specific fatty acids of serum lipids and serum high sensitivity C- reactive protein levels in morbidly obese women.
      ) have previously shown in a population of morbidly obese women that the n-6/n-3 PUFA ratio was positively correlated with C-reactive protein. It can therefore be hypothesized, as our population study is predominantly constituted of obese women, that the positive association found between the n-6/n-3 PUFA ratio and obesity is mediated by inflammatory pathways.
      Interestingly, our results showed that odd-chain FAs were negatively associated with obesity. Odd-chain FAs have recently gained interest as potential biomarkers for dairy product intake (
      • Pfeuffer M.
      • Jaudszus A.
      Pentadecanoic and heptadecanoic acids: multifaceted odd-chain fatty acids.
      ). Pentadecanoic acid and heptadecanoic acid are reported to be negatively associated with several disease outcomes, including diabetes, atherosclerosis, and cardiovascular diseases (
      • Jenkins B.
      • West J.A.
      • Koulman A.
      A review of odd-chain fatty acid metabolism and the role of pentadecanoic Acid (c15:0) and heptadecanoic Acid (c17:0) in health and disease.
      ). Our results concur with Kratz, Baars, and Guyenet (
      • Kratz M.
      • Baars T.
      • Guyenet S.
      The relationship between high-fat dairy consumption and obesity, cardiovascular, and metabolic disease.
      ), who reviewed 16 studies and reported that dairy fats might be associated with lower obesity risk, although Mika et al. (
      • Mika A.
      • Stepnowski P.
      • Kaska L.
      • Proczko M.
      • Wisniewski P.
      • Sledzinski M.
      • Sledzinski T.
      A comprehensive study of serum odd- and branched-chain fatty acids in patients with excess weight.
      ) found no difference in serum levels between individuals with and without obesity. This study suggests that the dietary source of the SFAs might determine their implication in obesity.
      The main strength of our study is that it includes data from a country where the incidence of obesity has increased tremendously within a short period of time, escalating from 40% to more than 65% in 40 years (
      • Di Cesare M.
      • Bentham J.
      • Stevens G.A.
      • Zhou B.
      • Danaei G.
      • Lu Y.
      • Bixby H.
      • Cowan M.J.
      • Riley L.M.
      • Hajifathalian K.
      Trends in adult body-mass index in 200 countries from 1975 to 2014: a pooled analysis of 1698 population-based measurement studies with 19.2 million participants.
      ), suggesting a lifestyle implication in this steady increase. The silhouettes available in our study showed that the majority of the participants were lean during childhood and adolescence and had developed obesity during life course, bringing upfront the implication of the environment and food consumption as promoter of the obesity in Mexico. However, our study is limited by its cross-sectional design. Blood samples and anthropometric measurements were collected together during recruitment, and therefore the association between obesity and FAs found should be interpreted in this specific context. The study was also limited by the lack of information on other biological makers, such as serum triglycerides, C-reactive protein, glucose, insulin, and cholesterol, which could have provided an input to the interpretation of the associations between FAs and obesity. In addition, as mentioned before, our population is homogenous and constituted predominantly of overweight and obese women, and the variability in FA levels in the population is low.
      In conclusion, this study showed a positive association between SCD-16 as a proxy for the endogenous production of palmitoleic acid and BMI. In addition, the n-6/n-3 PUFA ratio was positively associated with WHR, suggesting that n-6 PUFAs impact obesity depending on baseline concentration of n-3 PUFAs. Therefore, public health efforts toward adherence to a recommended n-6/n-3 PUFA ratio of one to four might reveal its importance in the fight against obesity. Nevertheless, the causality of the associations found in this study needs to be further investigated. Furthermore, more studies are required to evaluate the relation between obesity and various SFAs with a specific focus on dairy-sourced odd-chain FAs.

      Acknowledgments

      The authors would like to thank all the women who participated in the study, the National Council for Science and Technology for the financial support, Ms. Alessandra Campese, Michele Matta, Rachel Wasson, and Flavie Perrier for their technical support during the analysis of the data and the drafting of the manuscript, and all the physicians responsible for the project in the different participating hospitals: Dr. Germa'n Castelazo [Mexican Social Security Institute (IMSS), Mexico City, DF], Dr. Sinhué Barroso Bravo (IMSS, Mexico City, DF), Dr. Fernando Mainero Ratchelous (IMSS, Mexico City, DF), Dr. Joaquín Zarco Méndez [Institute for Social Security and Services for State Workers (ISSSTE), Mexico City, DF], Dr. Edelmiro Pérez Rodríguez (Hospital Universitario, Monterrey, Nuevo León), Dr. Jesús Pablo Esparza Cano (IMSS, Monterrey, Nuevo León), Dr. Heriberto Fabela (IMSS, Monterrey, Nuevo León), Dr. Fausto Hernández Morales (ISSSTE, Veracruz, Veracruz), Dr. Pedro Coronel Brizio (State Cancer Center, Health Services, Xalapa, Veracruz), and Dr. Vicente A. Saldaña Quiroz (IMSS, Veracruz, Veracruz).

      Supplementary Material

      REFERENCES

        • Di Cesare M.
        • Bentham J.
        • Stevens G.A.
        • Zhou B.
        • Danaei G.
        • Lu Y.
        • Bixby H.
        • Cowan M.J.
        • Riley L.M.
        • Hajifathalian K.
        Trends in adult body-mass index in 200 countries from 1975 to 2014: a pooled analysis of 1698 population-based measurement studies with 19.2 million participants.
        Lancet. 2016; 387: 1377-1396
        • Barquera S.
        • Campos I.
        • Rivera J.A.
        Mexico attempts to tackle obesity: the process, results, push backs and future challenges.
        Obes. Rev. 2013; 14: 69-78
        • Rtveladze K.
        • Marsh T.
        • Barquera S.
        • Sanchez Romero L.M.
        • Levy D.
        • Melendez G.
        • Webber L.
        • Kilpi F.
        • McPherson K.
        • Brown M.
        Obesity prevalence in Mexico: impact on health and economic burden.
        Public Health Nutr. 2014; 17: 233-239
        • Popkin B.M.
        • Adair L.S.
        • Ng S.W.
        Global nutrition transition and the pandemic of obesity in developing countries.
        Nutr. Rev. 2012; 70: 3-21
        • Stender S.
        • Astrup A.
        • Dyerberg J.
        Ruminant and industrially produced trans fatty acids: health aspects.
        Food Nutr. Res. 2008; 52: 1651
        • Melanson E.L.
        • Astrup A.
        • Donahoo W.T.
        The relationship between dietary fat and fatty acid intake and body weight, diabetes, and the metabolic syndrome.
        Ann. Nutr. Metab. 2009; 55: 229-243
        • Bingham S.A.
        • Day N.E.
        • Luben R.
        • Ferrari P.
        • Slimani N.
        • Norat T.
        • Clavel-Chapelon F.
        • Kesse E.
        • Nieters A.
        • Boeing H.
        Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study.
        Lancet. 2003; 361: 1496-1501
        • Baylin A.
        • Campos H.
        The use of fatty acid biomarkers to reflect dietary intake.
        Curr. Opin. Lipidol. 2006; 17: 22-27
        • Katan M.B.
        • Deslypere J.P.
        • van Birgelen A.P.
        • Penders M.
        • Zegwaard M.
        Kinetics of the incorporation of dietary fatty acids into serum cholesteryl esters, erythrocyte membranes, and adipose tissue: an 18-month controlled study.
        J. Lipid Res. 1997; 38: 2012-2022
        • Chajès V.
        • Biessy C.
        • Byrnes G.
        • Deharveng G.
        • Saadatian-Elahi M.
        • Jenab M.
        • Peeters P.H.
        • Ocke M.
        • Bueno-de-Mesquita H.B.
        • Johansson I.
        Ecological-level associations between highly processed food intakes and plasma phospholipid elaidic acid concentrations: results from a cross-sectional study within the European prospective investigation into cancer and nutrition (EPIC).
        Nutr. Cancer. 2011; 63: 1235-1250
        • Saadatian-Elahi M.
        • Slimani N.
        • Chajes V.
        • Jenab M.
        • Goudable J.
        • Biessy C.
        • Ferrari P.
        • Byrnes G.
        • Autier P.
        • Peeters P.H.
        Plasma phospholipid fatty acid profiles and their association with food intakes: results from a cross-sectional study within the European Prospective Investigation into Cancer and Nutrition.
        Am. J. Clin. Nutr. 2009; 89: 331-346
        • Chajès V.
        • Joulin V.
        • Clavel-Chapelon F.
        The fatty acid desaturation index of blood lipids, as a biomarker of hepatic stearoyl-CoA desaturase expression, is a predictive factor of breast cancer risk.
        Curr. Opin. Lipidol. 2011; 22: 6-10
        • Thiébaut A.C.
        • Rotival M.
        • Gauthier E.
        • Lenoir G.M.
        • Boutron-Ruault M.C.
        • Joulin V.
        • Clavel-Chapelon F.
        • Chajes V.
        Correlation between serum phospholipid fatty acids and dietary intakes assessed a few years earlier.
        Nutr. Cancer. 2009; 61: 500-509
        • Hjartåker A.
        • Lund E.
        • Bjerve K.S.
        Serum phospholipid fatty acid composition and habitual intake of marine foods registered by a semi-quantitative food frequency questionnaire.
        Eur. J. Clin. Nutr. 1997; 51: 736-742
        • Brevik A.
        • Veierod M.B.
        • Drevon C.A.
        • Andersen L.F.
        Evaluation of the odd fatty acids 15:0 and 17:0 in serum and adipose tissue as markers of intake of milk and dairy fat.
        Eur. J. Clin. Nutr. 2005; 59: 1417-1422
        • Wolk A.
        • Furuheim M.
        • Vessby B.
        Fatty acid composition of adipose tissue and serum lipids are valid biological markers of dairy fat intake in men.
        J. Nutr. 2001; 131: 828-833
        • Chajès V.
        • Biessy C.
        • Ferrari P.
        • Romieu I.
        • Freisling H.
        • Huybrechts I.
        • Scalbert A.
        • Bueno de Mesquita B.
        • Romaguera D.
        • Gunter M.J.
        Plasma elaidic acid level as biomarker of industrial trans fatty acids and risk of weight change: report from the EPIC Study.
        PLoS One. 2015; 10: e0118206
        • Mika A.
        • Sledzinski T.
        Alterations of specific lipid groups in serum of obese humans: a review.
        Obes. Rev. 2017; 18: 247-272
        • Do H.J.
        • Chung H.K.
        • Moon J.
        • Shin M.J.
        Relationship between the estimates of desaturase activities and cardiometabolic phenotypes in Koreans.
        J. Clin. Biochem. Nutr. 2011; 49: 131-135
        • Warensjö E.
        • Rosell M.
        • Hellenius M.L.
        • Vessby B.
        • De Faire U.
        • Riserus U.
        Associations between estimated fatty acid desaturase activities in serum lipids and adipose tissue in humans: links to obesity and insulin resistance.
        Lipids Health Dis. 2009; 8: 37
        • Vinknes K.J.
        • Elshorbagy A.K.
        • Nurk E.
        • Drevon C.A.
        • Gjesdal C.G.
        • Tell G.S.
        • Nygard O.
        • Vollset S.E.
        • Refsum H.
        Plasma stearoyl-CoA desaturase indices: association with lifestyle, diet, and body composition.
        Obesity (Silver Spring). 2013; 21: E294-E302
        • Schmitz G.
        • Ecker J.
        The opposing effects of n-3 and n-6 fatty acids.
        Prog. Lipid Res. 2008; 47: 147-155
        • Angeles-Llerenas A.
        • Ortega-Olvera C.
        • Perez-Rodriguez E.
        • Esparza-Cano J.P.
        • Lazcano-Ponce E.
        • Romieu I.
        • Torres-Mejia G.
        Moderate physical activity and breast cancer risk: the effect of menopausal status.
        Cancer Causes Control. 2010; 21: 577-586
        • Salazar-Martinez E.
        • Lazcano-Ponce E.C.
        • Gonzalez Lira-Lira G.
        • Escudero-De los Rios P.
        • Salmeron-Castro J.
        • Hernandez-Avila M.
        Reproductive factors of ovarian and endometrial cancer risk in a high fertility population in Mexico.
        Cancer Res. 1999; 59: 3658-3662
        • Hernández-Avila M.
        • Romieu I.
        • Parra S.
        • Hernandez-Avila J.
        • Madrigal H.
        • Willett W.
        Validity and reproducibility of a food frequency questionnaire to assess dietary intake of women living in Mexico City.
        Salud Publica Mex. 1998; 40: 133-140
      1. Lohman, T., A. Roche, and R. Martorell, . 1988. Anthropometric Standardization Reference Manual. Human Kinetics Books, Cham­paign, IL.

        • Stunkard A.J.
        • Sorensen T.
        • Schulsinger F.
        Use of the Danish Adoption Register for the study of obesity and thinness.
        Res. Publ. Assoc. Res. Nerv. Ment. Dis. 1983; 60: 115-120
        • Benjamini Y.
        • Hochberg Y.
        Controlling the false discovery rate: a practical and powerful approach to multiple testing.
        J. R. Stat. Soc. B. 1995; 57: 289-300
        • Smit L.A.
        • Willett W.C.
        • Campos H.
        trans-fatty acid isomers in adipose tissue have divergent associations with adiposity in humans.
        Lipids. 2010; 45: 693-700
        • Murakami K.
        • Sasaki S.
        • Takahashi Y.
        • Uenishi K.
        • Watanabe T.
        • Kohri T.
        • Yamasaki M.
        • Watanabe R.
        • Baba K.
        • Shibata K.
        Lower estimates of delta-5 desaturase and elongase activity are related to adverse profiles for several metabolic risk factors in young Japanese women.
        Nutr. Res. 2008; 28: 816-824
        • Micallef M.
        • Munro I.
        • Phang M.
        • Garg M.
        Plasma n-3 polyunsaturated fatty acids are negatively associated with obesity.
        Br. J. Nutr. 2009; 102: 1370-1374
        • Das M.
        • Pal S.
        • Ghosh A.
        Association of metabolic syndrome with obesity measures, metabolic profiles, and intake of dietary fatty acids in people of Asian Indian origin.
        J. Cardiovasc. Dis. Res. 2010; 1: 130-135
        • Sansone A.
        • Tolika E.
        • Louka M.
        • Sunda V.
        • Deplano S.
        • Melchiorre M.
        • Anagnostopoulos D.
        • Chatgilialoglu C.
        • Formisano C.
        • Di Micco R.
        Hexadecenoic fatty acid isomers in human blood lipids and their relevance for the interpretation of lipidomic profiles.
        PLoS One. 2016; 11: e0152378
        • Thompson A.K.
        • Minihane A.M.
        • Williams C.M.
        Trans fatty acids and weight gain.
        Int. J. Obes. (Lond). 2011; 35: 315-324
        • Ramírez-Silva I.
        • Villalpando S.
        • Moreno-Saracho J.E.
        • Bernal-Medina D.
        Fatty acids intake in the Mexican population. Results of the National Nutrition Survey 2006.
        Nutr. Metab. (Lond). 2011; 8: 33
        • Simopoulos A.P.
        The importance of the ratio of omega-6/omega-3 essential fatty acids.
        Biomed. Pharmacother. 2002; 56: 365-379
        • Mozaffarian D.
        • Aro A.
        • Willett W.C.
        Health effects of trans-fatty acids: experimental and observational evidence.
        Eur. J. Clin. Nutr. 2009; 63: S5-S21
        • Kavanagh K.
        • Jones K.L.
        • Sawyer J.
        • Kelley K.
        • Carr J.J.
        • Wagner J.D.
        • Rudel L.L.
        Trans fat diet induces abdominal obesity and changes in insulin sensitivity in monkeys.
        Obesity (Silver Spring). 2007; 15: 1675-1684
        • Dorfman S.E.
        • Laurent D.
        • Gounarides J.S.
        • Li X.
        • Mullarkey T.L.
        • Rocheford E.C.
        • Sari-Sarraf F.
        • Hirsch E.A.
        • Hughes T.E.
        • Commerford S.R.
        Metabolic implications of dietary trans-fatty acids.
        Obesity (Silver Spring). 2009; 17: 1200-1207
        • Collins J.M.
        • Neville M.J.
        • Hoppa M.B.
        • Frayn K.N.
        De novo lipogenesis and stearoyl-CoA desaturase are coordinately regulated in the human adipocyte and protect against palmitate-induced cell injury.
        J. Biol. Chem. 2010; 285: 6044-6052
        • Peter A.
        • Cegan A.
        • Wagner S.
        • Lehmann R.
        • Stefan N.
        • Konigsrainer A.
        • Konigsrainer I.
        • Haring H.U.
        • Schleicher E.
        Hepatic lipid composition and stearoyl-coenzyme A desaturase 1 mRNA expression can be estimated from plasma VLDL fatty acid ratios.
        Clin. Chem. 2009; 55: 2113-2120
        • Warensjö E.
        • Riserus U.
        • Gustafsson I.B.
        • Mohsen R.
        • Cederholm T.
        • Vessby B.
        Effects of saturated and unsaturated fatty acids on estimated desaturase activities during a controlled dietary intervention.
        Nutr. Metab. Cardiovasc. Dis. 2008; 18: 683-690
        • Flowers M.T.
        • Ntambi J.M.
        Stearoyl-CoA desaturase and its relation to high-carbohydrate diets and obesity.
        Biochim. Biophys. Acta. 2009; 1791: 85-91
        • Miyazaki M.
        • Ntambi J.M.
        Role of stearoyl-coenzyme A desaturase in lipid metabolism.
        Prostaglandins Leukot. Essent. Fatty Acids. 2003; 68: 113-121
        • Bagga D.
        • Wang L.
        • Farias-Eisner R.
        • Glaspy J.A.
        • Reddy S.T.
        Differential effects of prostaglandin derived from omega-6 and omega-3 polyunsaturated fatty acids on COX-2 expression and IL-6 secretion.
        Proc. Natl. Acad. Sci. USA. 2003; 100: 1751-1756
        • Calder P.C.
        Mechanisms of action of (n-3) fatty acids.
        J. Nutr. 2012; 142: 592S-599S
        • Iso H.
        • Rexrode K.M.
        • Stampfer M.J.
        • Manson J.E.
        • Colditz G.A.
        • Speizer F.E.
        • Hennekens C.H.
        • Willett W.C.
        Intake of fish and omega-3 fatty acids and risk of stroke in women.
        J. Am. Med. Assoc. 2001; 285: 304-312
        • Simopoulos A.P.
        An increase in the omega-6/omega-3 fatty acid ratio increases the risk for obesity.
        Nutrients. 2016; 8: 128
        • Yang B.
        • Ren X.L.
        • Fu Y.Q.
        • Gao J.L.
        • Li D.
        Ratio of n-3/n-6 PUFAs and risk of breast cancer: a meta-analysis of 274135 adult females from 11 independent prospective studies.
        BMC Cancer. 2014; 14: 105
        • Kaska L.
        • Mika A.
        • Stepnowski P.
        • Proczko M.
        • Ratnicki-Sklucki K.
        • Sledzinski T.
        • Goyke E.
        • Swierczynski J.
        The relationship between specific fatty acids of serum lipids and serum high sensitivity C- reactive protein levels in morbidly obese women.
        Cell. Physiol. Biochem. 2014; 34: 1101-1108
        • Pfeuffer M.
        • Jaudszus A.
        Pentadecanoic and heptadecanoic acids: multifaceted odd-chain fatty acids.
        Adv. Nutr. 2016; 7: 730-734
        • Jenkins B.
        • West J.A.
        • Koulman A.
        A review of odd-chain fatty acid metabolism and the role of pentadecanoic Acid (c15:0) and heptadecanoic Acid (c17:0) in health and disease.
        Molecules. 2015; 20: 2425-2444
        • Kratz M.
        • Baars T.
        • Guyenet S.
        The relationship between high-fat dairy consumption and obesity, cardiovascular, and metabolic disease.
        Eur. J. Nutr. 2013; 52: 1-24
        • Mika A.
        • Stepnowski P.
        • Kaska L.
        • Proczko M.
        • Wisniewski P.
        • Sledzinski M.
        • Sledzinski T.
        A comprehensive study of serum odd- and branched-chain fatty acids in patients with excess weight.
        Obesity (Silver Spring). 2016; 24: 1669-1676