Fad diets?

The 5:2 diet, also called the fast diet, is a type of intermittent fasting known as alternate-day fasting.

On this diet, you eat normally for five days a week and restrict your calorie intake to 500–600 calories for two days each week, resulting in an overall calorie deficit that leads to weight loss.

The 5:2 diet is considered a form of modified alternate-day fasting. By contrast, some types of alternate-day fasting involve going without food for a full 24 hours.

The extremely low calorie allotment on the two “fast” days has led some to classify the 5:2 diet as a fad diet.

However, the evidence supporting the health benefits of alternate-day fasting is growing, and it seems to be a legitimate option for weight loss (31).

Research suggests that alternate-day fasting doesn’t cause excessive calorie intake on eating days. This may be due to the release of peptide YY (PYY), a hormone that makes you feel full and helps you eat less (32).

Importantly, alternate-day fasting hasn’t been shown to cause greater weight loss than standard diets containing the same number of calories.

However, several studies have found that both approaches can be effective for losing weight and belly fat (33, 34).

What’s more, although it isn’t possible to completely prevent loss of muscle while losing weight, alternate-day fasting seems to be superior for maintaining muscle mass when compared to conventional forms of calorie restriction (33, 34).

You can learn more about the 5:2 diet by reading this article.