Dietary Intake, Fatty Acid Biomarkers, and Abdominal Obesity Population-Based Observational Studies

Alsharari, Z. 2017. Dietary Intake, Fatty Acid Biomarkers, and Abdominal Obesity. Population-Based Observational Studies. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine 1349. 47 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-513-0024-5. The aim of this thesis was to investigate the associations between fatty acid (FA) biomarkers, carbohydrate intake, and abdominal obesity (AO) and related anthropometric measures in a population-based cohort of men and women in Stockholm County. The overall hypothesis was that dietary fat quality assessed by serum and adipose tissue FA composition, and dietary intake of especially carbohydrates is associated with AO. FA composition was assessed by liquid gas chromatography, and AO was measured as waist circumference (WC), waist hip ratio (WHR) and sagittal abdominal diameter (SAD). Dietary intake was assessed by 7-day food records. Papers I, II, III, and IV were all observational studies based on a Swedish population in Stockholm County (n=5460). A sub-cohort of only men (n=301) was included in Papers II, III, and IV. In Paper I, serum proportions of the polyunsaturated FA (PUFA), linoleic acid (LA) (18:2n6), was inversely associated with AO in both men and women, whereas a positive association was observed between the saturated FA (SFA), palmitic acid (PA) (16:0) and AO measures. These findings support recent interventional studies suggesting that a higher relative intake of PUFA (LA) from vegetable oils as compared with 16:0 is associated with decreased abdominal adiposity. In Paper II, we investigated whether biomarkers of dietary fat quality were related to the corresponding FA intake from fat-rich foods reported in a short food frequency questionnaire (FFQ). Serum proportions of the long-chain n-3 PUFAs eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA) were higher among men with higher total fish intake. Serum LA was higher among men who reported a consumption of more than 5 g/d of margarine. Absolute agreement between intakes assessed with FFQ of 60YO and 7-day food record of "Kost och Metabola syndromet"/"Diet and the Metabolic syndrome" (KOMET) was highest for alcohol, total fish, and eggs. Weighted Kappa statistics revealed the strongest agreement for alcohol, margarine, and fruits. In Paper III, carbohydrate intake was inversely associated with 16:0 in serum phospholipids (PL). Disaccharide and alcohol intake was positively and non-linearly associated with palmitoleic acid (16:1) and stearoyl-CoA-desaturase (SCD) activity in PL. Alcohol was consistently associated with higher SFA and monounsaturated FA (MUFA). Results of Paper IV indicated that total carbohydrate intake was inversely associated with measures of AO and central fat distribution, WHR and SAD, respectively. Likewise, monosaccharide intake was associated with lower AO. In contrast, alcohol intake was associated with AO prevalence and all anthropometric measurements. In conclusion, serum SFA (palmitic acid) was positively associated with AO, whereas n-6 PUFA (linoleic acid) was associated with lower AO. High intake of total carbohydrate and monosaccharides were associated with lower AO. Overall, these results support a beneficial role on adiposity of diets that are higher in polyunsaturated fat (vegetable oils) and total carbohydrates compared with saturated fat.