Do crash diets work?

Crash dieting

“Crash diets might not be so bad in beating fat after all”

- The Independent, 16 October 2014

The BHF’s view:

This research was widely reported, including in the Mail, Telegraph and Express. Example headlines included “Crash dieting more effective than gradual weight loss” and “Crash dieting is the best way to lose weight”.

There is a lot more to this research than the headlines suggest and the current advice to make achievable, long-term changes to your diet and activity levels still stands.

In the Australian study, 200 obese adults were randomly assigned to either a 12-week rapid weight loss programme on a very low calorie diet (based on three meal-replacement shakes each day) or a 36-week diet that reduced their daily intake by 500 calories. They were all aiming to lose at least 12.5 per cent of their body weight.

The people that achieved this in the time frame were then monitored for nearly three years (144 weeks) to see whether they put the weight back on. By the end, the results were very similar for both groups – the majority (71 per cent) of people had put the weight back on.

Not all the news coverage was accurate. The Express said: “Crash dieting is the best way to lose weight”, but the study did not prove this, and certainly not in terms of long-term outcomes. The Telegraph focused on the fact that more of the rapid dieters achieved their goal – but this was only after the initial period.

The research itself had some shortcomings. The study did not include people who smoked, had diabetes, or were severely obese, so it is hard to know whether the findings would apply to those people. Even a 36-week weight loss programme, which was the ‘gradual’ option, may be too rapid for some people.

One person in the crash diet group suffered from gallbladder inflammation and had to have this organ removed. This incident was cited as “probably related” to the crash diet. Crash diets can have a number of other downsides too, including muscle loss and missing out on essential nutrients, yet the study did not seem to monitor these factors.

The research also didn’t look at the ways that physical activity can help with weight loss. Only about half of people achieved the 12.5 per cent weight loss and also stayed in the study for the follow-up period (61 people in the rapid group, and 43 in the gradual group).

A larger study might have yielded different results. Victoria Taylor, our Senior Dietitian, said: “Quick fixes can be appealing when it comes to weight loss. Changing eating habits and lifestyles can be a challenge and take time, but it’s important to consider long-term health as well as your weight.

That’s why we encourage people to forget fads and instead recommend a sustainable approach to weight loss. Making small, achievable changes to diet and activity levels can make a long-term difference and means you get a good balance of nutrients.”

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