Investigating intermittent fasting for body composition and overall health

Obesity^[1] has been described as a public health crisis, with its prevalence increasing in many parts of the world. It has been well-established that obesity increases the risk of numerous health conditions^[2], including insulin resistance and type 2 diabetes, dyslipidemia, and cardiovascular disease. With this in mind, it’s no surprise that obesity has been associated with a lower quality of life^[3] and with a lower life expectancy^[4]. Importantly, sustained modest weight loss of 5-10% can reduce^[5] the incidence and progression of many of these conditions, including type 2 diabetes^[6] in people with prediabetes.

Although weight loss is beneficial, many people have a hard time adhering to diets^[7] that involve daily energy restriction in the long term. One possible alternative approach is intermittent fasting (IF)^[8], which is an eating pattern that involves alternating periods of little or no energy intake with intervening periods of normal food intake, on a recurring basis.

Studies in mice suggest that IF may be similarly, or even more, effective than isoenergetic (i.e., providing the same number of calories) daily caloric restriction (DCC) for improving insulin sensitivity^[9] and cardiovascular health^[10], and that these beneficial effects may take place even without weight loss. Similarly, most studies in humans report that intermittent fasting^[11] lowers bodyweight and improves cardiometabolic health. However, the underlying mechanisms are unclear, with some studies^[12] suggesting that intermittent fasting’s effects are solely the result of net caloric restriction, and with other studies^[13] proposing that “metabolic switching” between fed and fasted states rather than weight loss per se may underpin intermittent fasting’s health benefits.

To test these competing hypotheses and to investigate the effects of metabolic switching, the study under review compared intermittent fasting with continuous food intake at two different energy intakes: 30% caloric restriction and neutral energy balance.

Intermittent fasting involves alternating periods of eating with periods of fasting. Studies in animals and humans suggest that intermittent fasting (IF) can reduce weight and fat mass, and may improve several markers of health. However, it’s not clear if these beneficial effects are because of caloric restriction and the accompanied weight loss or independent of them. The study under review aimed to investigate the effects of intermittent fasting on health and body composition by comparing intermittent fasting with continuous food intake in an energy deficit and in energy balance.