Dietary Fatty Acids, Body Composition and Ectopic Fat Results from Overfeeding Studies in Humans

Rosqvist, F. 2016. Dietary Fatty Acids, Body Composition and Ectopic Fat . Results from Overfeeding Studies in Humans. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine 1358. 94 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-554-9523-7. The aim of this thesis was to investigate the effects of dietary fatty acids on body composition and ectopic fat in humans, with emphasis on the role of the omega-6 polyunsaturated fatty acid (PUFA) linoleic acid (18:2n-6) and the saturated fatty acid (SFA) palmitic acid (16:0). The overall hypothesis was that linoleic acid would be beneficial compared with palmitic acid during overfeeding, as previously indicated in animals. Papers I, II and IV were double-blinded, randomized interventions in which different dietary fats were provided to participants and Paper III was a cross-sectional study in a communitybased cohort (PIVUS) in which serum fatty acid composition was assessed as a biomarker of dietary fat intake. In Paper I, overfeeding with sunflower oil (n-6 PUFA) for 7 weeks caused less accumulation of liver fat, visceral fat and total body fat (as assessed by MRI) compared with palm oil (SFA) in young and lean subjects despite similar weight gain among groups. Instead, sunflower oil caused a larger accumulation of lean tissue. In Paper II, plasma from Paper I was analyzed with NMR-based metabolomics, aiming to identify metabolites differentially affected by the two dietary treatments. Acetate decreased by PUFA and increased by SFA whereas lactate increased by PUFA and decreased by SFA. In Paper III, the proportion of linoleic acid in serum was inversely associated with contents of visceral-, subcutaneousand total body adipose tissue whereas the proportion of palmitic acid was directly associated with visceraland total body adipose tissue in 70-year old men and women. In Paper IV, overfeeding with sunflower oil for 8 weeks caused less accumulation of liver fat compared with palm oil also in overweight and obese subjects. SFA increased visceral fat in men only. Accumulation of lean tissue was similar between groups. In conclusion, SFA (palmitic acid) from palm oil promotes marked liver fat accumulation in both normal-weight and overweight/obese subjects during overeating, whereas n-6 PUFA (linoleic acid) from sunflower oil prevents such liver fat accumulation. Diverging effects of SFA and PUFA on visceral adipose tissue and lean tissue may only be applicable in some groups and/ or circumstances. These results imply that negative effects associated with weight gain (e.g. fatty liver) may be partly counteracted by the type fat in the diet, overall supporting a beneficial role of diets higher in unsaturated fat compared with saturated fat for preventing liver fat accumulation.