Dietary concepts using modulation of macronutrient composition without energy restriction. There appear to be relevant interspecies differences when comparing metabolic effects of specific fatty acids. For example, in humans, n-6 PUFA may improve insulin resistance and diabetes risk, whereas n-3 PUFA from marine origin improve insulin sensitivity in rodent models but not in humans. No long-term-randomized trials have been published to date that investigated the effect of dietary fat composition on diabetes risk. High-fiber diets and particularly diets high in insoluble cereal fiber appear to improve whole-body insulin sensitivity, possibly by interference with the digestion and/or absorption of dietary protein and as such preventing the amino-acid-induced activation of the mTOR/S6K1 signalling pathway. Separating the effects of high-fiber diets from potentially independent effects of diets varying in the glycemic index (GI) is challenging. In rodents, changes in the composition of the gut microbiota and colonic fermentation with the production of short chain fatty acids (SCFA) appear to be involved, but it remains to be shown whether this applies also in humans. Adverse effects of high-protein diets on insulin sensitivity may be partly compensated by satiating effects of dietary protein and consequent weight loss, and increases in lean mass, but long-term maintenance of weight loss with any diet appears to be difficult to achieve. MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; TFA, trans unsaturated fatty acids; SFA, saturated fatty acids; GI, glycemic index; BCAA, branched chain amino acids.
