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Eat a day, skip a day?

Typical dieting can be a chore. An alternative is to eat less (or not at all) during certain time periods, otherwise known as fasting. This is the first trial to compare regular calorie restriction to alternate-day fasting.

Study under review: A Randomized Pilot Study Comparing Zero-Calorie Alternate-Day Fasting to Daily Caloric Restriction in Adults with Obesity

Introduction

The mythical 'optimal diet' has little to do with macronutrient, energy or vitamin content. Instead, the ideal diet is determined by what the dieter can, and will, actually stick to. This idea is supported by studies such as the A to Z weight loss study[1] and the BBC weight loss study[2]. Those studies focused on macronutrient content, type of diet, or food group elimination, and were generally in line with the current guidelines for treatment of obesity, which recommend a moderate daily caloric restriction (20-30% energy deficit below requirements for weight maintenance).

In most cases, consistent daily calorie reduction is typically able to produce moderate weight loss over time. However, intermittent calorie restriction[3] is another option that may work well for some people. Intermittent fasting has been growing in popularity, and can be practiced in a number of different ways.

Among the most[4] studied forms[5] of fasting are alternate day fasting (ADF) and alternate day modified fasting, which involve either complete fasting or the consumption of only 25% of one's individual energy requirements, respectively. Multiple studies have shown that ADF may reduce the risk of diabetes[6] and cardiovascular diseases[7]. Time-restricted eating windows[8] are another form of fasting, in which a person eats all of their food within a daily eating window of 8 to 12 hours. This method has been growing in popularity, though the most impressive research on time-restricted eating windows still exists mainly in animal models. A review[9] comparing intermittent vs. daily calorie restriction concluded that, although they have similar effects on total bodyweight reduction, intermittent calorie restriction is more effective for retaining lean mass. Some people might also find it easier to adhere to intermittent compared to daily calorie restriction for short treatment durations (e.g. 12 weeks), due to its favorable effects on hunger and satiety hormones[10].

A number of studies over the past ten years have shown the beneficial effects of ADF, but randomized trials comparing ADF and daily calorie restriction are needed in order to show greater efficacy. Accordingly, the aim of this pilot study was to evaluate the safety and tolerability of an eight week ADF program and compare it with moderate daily caloric restriction in its effects on body weight, body composition, lipids, and insulin sensitivity. The study also aimed to assess risk for weight regain between groups after 24 weeks of unsupervised follow-up. To gain insight into potential mechanisms of action, changes in resting metabolic rate (RMR) were measured along with leptin and ghrelin, which are hormones involved in energy balance, and brain-derived neurotrophic factor (BDNF), which has been suggested to mediate fasting-induced improvements in cognitive function[11] as well as playing a role in energy[12] balance[13].

Alternate-day fasting (ADF) is a form of intermittent fasting where a person either fasts completely or limits food intake to approximately 25% of daily needs every other day, allowing ad libitum food intake on alternating days. A number of trials have shown benefit, but a randomized controlled trial directly comparing ADF to continuous daily calorie restriction had yet to be reported.

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