Intermittent fasting and 'metabolic switch': Effects on metabolic syndrome, prediabetes and type 2 diabetes

Various intermittent fasting (IF) dietary plans have gained popularity among obese individuals in recent years as a means of achieving weight loss. However, studies evaluating the effect of IF regimens in people with metabolic syndrome, prediabetes and type 2 diabetes (T2D) are limited. The aim of the present review was to briefly elucidate the biochemical and physiological mechanisms underlying the positive effects of IF, especially the effect of the proposed 'metabolic switch' on metabolism. Next, we examined the efficacy and safety of IF regimens in individuals with metabolic syndrome, prediabetes and T2D. To achieve this, we performed a MEDLINE PubMed search using combinations of various IF terms, including trials in which participants met the additional criteria for metabolic syndrome, prediabetes or T2D. We found four studies in individuals with metabolic syndrome, one study in people with prediabetes, and eight studies in people with T2D evaluating the effects of different IF regimens. The limited available evidence, with small sample sizes and short trial durations, suggests that IF regimens have a similar effectiveness compared with calorie-restriction diets for weight loss and improvement in glycaemic variables. In general, most IF regimens are effective and safe. However, there is an increased risk of hypoglycaemia in patients with T2D who are treated with insulin or sulphonylureas. Moreover, long-term adherence to these regimens appears uncertain. There is a need for large controlled randomized trials to evaluate the efficacy of IF regimens, especially in individuals with metabolic syndrome and prediabetes. If proven to be sustainable and efficacious for prolonged periods, IF could offer a promising approach to improving health at the population level, and would result in multiple public health benefits.