Fasting 2 days a week can help obese people keep off the weight with modest results, study finds

By Katie Hunt, CNN

The 5:2 diet, a type of intermittent fasting, is no more effective than traditional approaches to weight loss, according to what researchers said was the first study of the regimen in a “real-life setting.”

However, the researchers found that the approach, which involves two days of heavily restricting calories (500 calories for women, 600 calories for men) and five days of sensible eating, was rated more highly by the obese people in the study because it was easy to follow.

“Here we’ve been able to provide the first results on the effectiveness of simple 5:2 diet advice in a real-life setting. We found that although the 5:2 diet wasn’t superior to traditional approaches in terms of weight loss, users preferred this approach as it was simpler and more attractive,” said Katie Myers Smith, a chartered health psychologist and senior research fellow at Queen Mary University of London, in a news statement. She was an author of the study that published in the scientific journal PLOS ONE.

Doctors may want to consider including the 5:2 diet as part of their standard weight management advice to patients, she said.

The study involved 300 obese people in Tower Hamlets, an inner city area of high deprivation in London. The participants either followed the 5:2 regimen or a more conventional approach to losing weight that stressed eating more vegetables and whole-grain foods, cutting out foods high in sugar and fat, eating smaller portions and exercise.

‘Modest’ results

The results of both approaches were very similar and “modest,” the study said.

At six months, those using the 5:2 diet had lost, on average, 1.8 kilograms (4 pounds) compared to 1.7 kilograms (3.7 pounds) on the standard diet advice. At 12 months, those figures were 1.9 kilograms (4.2 pounds) and 1.8 kilograms (4 pounds), respectively.

Some 18% of 5:2 dieters had lost at least 5% of their body weight after one year compared to 15% using the conventional approach.

Of the group following the 5:2 diet, half attended six group support sessions for the first six weeks after the initial information session. However, its impact of the group support diminished over time, the study found.

Participants were positive about the different weight loss approaches, but those on the 5:2 diet were more likely to recommend it to others and said they were more likely to continue with the approach.

The study was a randomized control trial, regarded as the most rigorous kind of research, and while the number of participants was larger than most previous studies of intermittent fasting, the authors said “some findings of borderline significance could have become clearer if the sample size was larger.”

The people following the conventional weight loss guidance were also more likely to try other strategies such as Weight Watchers, Slimming World or other diets. This factor could have masked the effects, but it would not have been ethical or practical to stop participants trying alternative approaches, the study authors said.

Intermittent fasting

Some experts think that alternating between fasting and eating can improve cellular health by triggering metabolic switching.

In metabolic switching, cells use up their fuel stores and convert fat to energy — “flipping a switch” from fat storing to fat saving. Intermittent fasting can reduce blood pressure, aid in weight loss, and improve longevity, a review of past animal and human studies published in The New England Journal of Medicine suggests.

The method is not appropriate for everyone, however, particularly pregnant women and those with medical conditions such as diabetes or eating disorders.

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