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Deep Dive: How does alternate-day fasting compare to no diet or other diets?

ADF helps people lose weight and lower cholesterol, but there's no clear advantage over continuous energy restriction based on the current evidence. Larger, longer studies are needed, though.

Study under review: Effect of alternate-day fasting on obesity and cardiometabolic risk: A systematic review and meta-analysis

Introduction

Intermittent fasting (IF) is a popular strategy for weight loss. The term encompasses different specific diets characterized by periods of eating interspersed with longer periods of fasting, which are mapped out in Figure 1. A less common diet in humans, but one used for longer durations in animal models[1], is alternate-day fasting (ADF). As its name implies, ADF consists of fasting for one day and eating the next day. This can either mean fasting for 24 hours and eating for 24 hours, or most commonly, fasting for 36 hours and eating for 12 hours. One modification, used clinically to increase adherence, involves eating a small amount of calories on the fasting day (about 25% of standard, also called modified ADF). Although there is a lot of experimental support[1] for the usefulness and efficacy of ADF in animal models, its effects in humans are still controversial.

Figure 1: How modified ADF relates to IF

There have been several meta-analyses comparing intermittent energy restriction (IER) interventions, which include IF and ADF, to continuous energy restriction (CER) for weight loss and cardiometabolic risk markers. Several have been covered in Study Deep Dives. However, these papers tend to lump together all types of IER, complicating interpretation of the results, and include different types of studies. To find a more specific answer to the question “Does ADF work for humans?”, the authors of this meta-analysis compared the effects of ADF against CER or control on weight-related parameters and cardiometabolic risk markers.

A popular means of weight loss is to incorporate regular periods of fasting. Alternate day fasting (ADF), in which food is ingested every other day, has been used in research and in some human trials. However, ADF has not been meta-analyzed separately from other types of IER, and randomized controlled studies specifically on ADF have not been meta-analyzed.

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