It’s been over two years since the 5:2 diet first hit bookshelves, kick-starting an intermittent fasting fad that’s swept the mainstream media and attracted a host of A-list devotees, from Beyoncé to Benedict Cumberbatch. But does it actually work? How hard is it to stick to? And most importantly, can it help you lose weight?

The Theory

The most popular form of fasting diet. On two days a week you eat 600 calories; on the other five you have your normal food intake. The principle is that it’s easier to burn fat because your body is in a post-absorptive state where your insulin levels are low. There’s also some evidence that, by mimicking a “starvation” state, fasting can provide the same protective effects against dementia and cancer as extreme calorie restriction, without the unpleasantness.

The Good

As diets go, the 5:2 plan is very simple to understand and no specific food groups are demonised.

“Some people find that sticking to a calorie controlled diet for just two days a week is a lot easier than following it for a whole week,” says dietitian Chloe Miles of the British Dietetic Association.

There have also been some promising results from studies on intermittent fasting.

“A few studies have found that it achieves a similar amount of weight loss to a standard calorie-controlled diet,” says Miles. “And some studies have suggested that the 5:2 diet may improve insulin sensitivity and reduce the risk of obesity-related cancers, such as breast cancer.”

The Bad

The lack of guidance on what constitutes a healthy diet can torpedo weight-loss efforts.

“Some people interpret the diet to mean that they can eat as much as they like on non-fast days,” says Miles. “This is not going to result in weight loss and is not a healthy approach to eating.”

Meanwhile, fasting is not a pleasant experience. “On fast days people may be irritable, feel dizzy and find it difficult to concentrate,” says Miles.

While there are some studies that support the 5:2 diet, the evidence is not conclusive.

“The studies that have looked at the 5:2 diet are limited and we do not know the effects of following this diet in the long term,” says Miles. “Many of the studies only include a small number of participants or are animal studies.”

The Expert Verdict

If you plan your diet carefully, intermittent fasting might well help you lose weight, as will any calorie-restricting plan. But the 5:2 diet is not something that Miles would recommend.

“For some people it may work and they may be able to follow it in a healthy, balanced way. For other people it may exacerbate disordered eating and lead to an obsession with dieting and food.

“Due to the limited evidence base at present, I don’t think it should be recommended as the first approach to losing weight.”

The Experience

To find out what the 5:2 diet is really like, we asked one writer to try it for 28 days, and compared it to four other writers trying different four-week diets. Click the link below to find out how they got on.

RECOMMENDED: The Best Four-Week Diet Plan

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