Fasting: the fast-track to muscle loss?

Obesity is a major health problem worldwide, contributing to the development of most modern chronic diseases. Obesity is driven by a chronic positive fat balance (more energy being stored than mobilized from fat tissue), in which overconsumption of energy promoted by the current food environment appears to play a significant role^[1]. Whereas caloric restriction and subsequent weight loss can be achieved by different types of diets, the main difficulty^[2] in the treatment of obesity is the lack of long-term compliance and maintenance of the weight lost. You can check out how successful weight loss looks compared to typical weight regain in Figure 1.

One way in which long-term dietary adherence can be increased is by tailoring the intervention to each person’s preferences. Some people prefer using interventions that include only intermittent periods of dietary restriction. These interventions, commonly grouped together as intermittent energy restriction (IER) paradigms, can be of many different forms that are all based around alternating periods of caloric restriction with periods of caloric balance or unrestricted eating. Common examples include the 5:2 diet (five days of unrestricted eating with two days of severe caloric restriction), time-restricted feeding (daily fasting window of approximately 12-16 hours), every-other-day fasting, and variations of the three. IER interventions attempt to promote adherence by decreasing the amount of dieting periods, while tentatively also decreasing adaptations induced by the restriction of calories, like the reduction^[3] in resting energy expenditure.

Overall, current evidence^[4][5] suggests that there is no significant difference with regard to weight loss between IER and continuous energy restriction (CER). However, within IER diets, there are those that alternate periods of caloric restriction with periods of caloric balance (regular intermittent dieting), and those in which periods of dieting are interspersed with days of more severe caloric restriction (intensified intermittent dieting). These two types of IER might show different results when compared to CER, and previous meta-analyses haven’t analyzed them separately. Therefore, the authors of the current systematic review and meta-analysis aimed to compare the effects of different types of IER versus CER on weight loss, body composition, and energy expenditure.

Obesity is a major health problem worldwide, and its treatment is primarily limited by low long-term adherence to dietary interventions. Intermittent energy restriction (IER) interventions are those in which dietary restriction periods are interspersed with periods of unrestricted or caloric balance (regular IER), in an attempt to reduce the time spent dieting. However, there are also IER interventions that involve periods of caloric restriction alternated with periods of even more severe caloric restriction (intensified IER). While previous meta-analyses do not appear to show any significant difference between regular IER and continuous energy restriction, they haven’t tested the effect of intensified IER separately.