Does Intermittent Fasting Work?

Obesity is a major global health issue. The World Health Organisation estimates that worldwide, over 650 million adults are obese. Most developed countries have overweight and obesity prevalence rates approaching 50% and within the MENA region it is estimated that 30% of the population is obese. With increasing obesity rates, comes higher rates of type 2 diabetes and heart disease globally, putting a major strain on health services and medical provisions.

Invasive surgical approaches to counteract the obesity crisis are not suitable for all. Perhaps a better option is to improve education on healthy weight loss programmes, with a better understanding of the dietary approaches currently available.

At one time, dieting involved a daily restriction of calorie intake. This is a technique that works for many; however, questions remain over its long-term applicability. Is it feasible for people to live in a perpetual state of calorie counting? Once people stop restricting their calories, many find that they rapidly regain the weight they have lost. Intermittent fasting may provide an alternative option for those who struggle with long term adherence to traditional calorie restriction.

What is intermittent fasting?

Intermittent fasting is classed as a diet, but is, more accurately, an eating pattern, comprising of periods of fasting and periods of eating ad libitum (“at one’s pleasure”).

There are three main fasting methods:

  • 16/8 method (time-restricted feeding). People who follow this approach fast for 16 hours and eat for 8 hours. In fact, whilst 16 hours is suggested, those who do time-restricted feeding fast for anything from 12 to 21 hours. It is the most popular form of intermittent fasting.
  • Eat-stop-eat (alternate day fasting). This concept involves fasting for 24 hour periods, once or twice a week. Although participants can eat what they like on the non-fast days, studies suggest that most people naturally reduce their calorie intake on the days in between.
  • 5:2 diet (modified fasting). Those who adopt this approach reduce their energy intake by 70-75% for two non-consecutive days each week. On the fasting days they limit themselves to between 500 and 600 calories, eating ad libitum on the remaining days.

Does it work?

There are a number of ‘fad’ diets available today, popularised by celebrities, bloggers and the media. The problem with many of these diets is that they are lacking the scientific evidence to support their claims. For a detailed review on some of the most well known of these diets, click here.

So, how does intermittent fasting compare? Is it just another fad, or is it a realistic alternative to the days of stringent calorie counting and abstinence?

Well, preliminary results are encouraging. Studies have demonstrated that the weight loss observed after 2 – 3 weeks of intermittent fasting is comparable to that seen with daily calorie restriction. It also seems to be equally effective at modulating obesity-associated disease risk, for example, lowering blood pressure and reducing the levels of insulin and glucose in the blood. When considering trials that looked at intermittent fasting, 73% of them had participants that experienced a statistically significant reduction in weight. Although, differences between the studies makes cross-comparison difficult.

The major issue is that there are a limited number of human studies looking at the effectiveness of intermittent fasting, meaning there is a shortage of evidence-based support for the process. Much of the work on the effects of fasting to date, has been performed using animals, which, whilst encouraging, can not definitively replicate the complexity of the human body. Safety data is also lacking, as are studies exploring which type of fasting regime is most effective. It has been proposed that intermittent fasting can improve cognitive performance and cardiovascular outcomes; however, this is yet to be confirmed experimentally.

Take home message

Intermittent fasting may turn out to be a weight management tool that helps to tackle the global burden of obesity. It is an appealing option for those who struggle with the concept of constant dieting; and, despite the fact that ‘normal’ eating is encouraged on non-fast days or for non-fast hours, most people naturally eat more healthily, thus, lowering their calorie consumption. For those that skip breakfast, there is no evidence that they consume more at lunch time to compensate. Considering the positive results from studies such as these, initial results are encouraging. However, the scientific evidence is currently lacking in terms of longer-term human studies.

Provided the fasting is not excessive, side effects are minimal, possibly involving headaches, weakness, dehydration and hunger pangs, although these should be short-lived. However, if the fast is practiced too frequently, or over consecutive days, there is a risk of malnutrition and in extreme cases, organ damage. Thus, it is essential to fast safely and follow the recommended guidelines for your regime of choice.

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  • “Obesity and Overweight.” World Health Organization,
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  • Templeman, Iain, et al. “The Role of Intermittent Fasting and Meal Timing in Weight Management and Metabolic Health.” Proceedings of the Nutrition Society, 26 Apr. 2019, pp. 1–12., doi:10.1017/s0029665119000636.
  • Varady, K. A. “Intermittent versus Daily Calorie Restriction: Which Diet Regimen Is More Effective for Weight Loss?” Obesity Reviews, vol. 12, no. 7, July 2011, pp. e593–601., doi:10.1111/j.1467-789x.2011.00873.x.
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