What dietary modification best improves insulin sensitivity and why?

Insulin resistance (IR) has been proposed as the strongest single predictor for incident type 2 diabetes and is mainly caused by adiposity as a result of chronic excessive energy intake. Loss of body weight and fat mass improve insulin sensitivity. However, independent of energy intake and changes in body weight/composition, dietary content and specific metabolic effects of certain nutrients may play significant additional roles in influencing IR. These effects are mainly relatively modest, with modulation of IR and diabetes risk within the range of 10-30%, but could be of major relevance on a population level. Examples include dietary concepts and patterns such as the traditional Mediterranean diet; the isoenergetic modulation of the composition of types of fatty acids in the diet; low-carbohydrate-high-protein diets; the quality of carbohydrate-rich foods, which includes the concepts of glycaemic index (GI) and glycaemic load; and, not necessarily related to the GI concept, specific metabolic effects of high-fibre diets, with relevant differences between the type of fibre consumed. Effects of further selected foods (e.g. coffee, tea and nuts) and micronutrients (e.g. magnesium, selenium and zinc) on the modulation of IR have been reviewed elsewhere. This study focuses on changes in IR by isoenergetic modulation of the main macronutrients (fat, carbohydrates including dietary fibre, and dietary protein), with discussion of novel concepts and the potential interplay of food components in the current dietary concepts.