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Brief 5:2 diet advice is as effective as traditional GP advice, but people like it better

A clinical trial has found people prefer receiving information on the 5:2 diet than standard GP weight management advice despite both interventions achieving similar modest weight loss results.

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Fresh fruit and vegetables.
Fresh fruit and vegetables.

The trial, funded by the Medical Research Council (MRC) and led by Queen Mary University of London, is the first randomised evaluation of the 5:2 diet, a popular type of intermittent fasting regime. Researchers studied the long-term effects of providing 5:2 diet instructions compared to traditional weight loss advice in 300 UK adults with obesity over a one-year period.

The findings show that long-term weight loss was similar for those who received 5:2 diet or standard weight management advice with 18 per cent and 15 per cent of participants respectively losing at least five per cent of their body weight at one year. However, when asked to rate each intervention, participants in the 5:2 diet group were more likely to recommend the intervention to others or be willing to continue with their diet.

Previous evidence suggests that peer support could be important for encouraging dieters to adhere to and realise the effects of the 5:2 diet. To test this, the researchers studied the impact of a weekly support group in addition to the simple 5:2 diet advice. They found that whilst initially face-to-face support generated better early effects and improved adherence to the 5:2 diet, these effects weakened over time.

Together, the findings suggest that providing brief advice on the 5:2 diet could extend the options clinicians can offer to patients.  

Dr Katie Myers Smith, Chartered Health Psychologist and Senior Research Fellow at Queen Mary, said: “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. Based on these findings, GPs may consider recommending the 5:2 diet as part of their standard weight management advice.”

The 5:2 diet 

The 5:2 diet is popular intermittent fasting weight loss intervention whereby dieters restrict their caloric intake on two non-consecutive days a week and then apply sensible eating on the remaining days. It first became popular in the UK through a BBC Horizon documentary and follow-up bestselling book.

In the study, traditional weight management advice on diet and exercise consisted of a 20-minute session where patients where an advisor explained the programme and went over key tips provided in supporting materials including the British Heart Foundation guides ‘Facts Not Fads’ and ‘Get Active, Stay Active’, the NHS ‘Change 4 Life’ series of booklets and a leaflet listing local resources for exercise. Participants in the 5:2 group instead received a leaflet on restricting their caloric intake on two non-consecutive days a week, with examples of meals containing the required amount of calories, and pointers to additional online support as part of an individual 20-minute session.

More information

  • The research was funded by the Medical Research Council.
  • Research publication: ‘A randomised controlled trial of the 5:2 diet’ Peter Hajek, Dunja Przulj, Francesca Pesola, Hayden McRobbie, Sarrah Peerbux, Anna Phillips-Waller, Natalie Bisal and Katie Myers Smith. PLOS ONE (2021). DOI: 10.1371/journal.pone.0258853.


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