Select Committee on Health Minutes of Evidence


Memorandum by Dr Helen Truby (OB 103)

REVIEW OF THE BBC DIET TRIALS

  The study entitled A randomised controlled trial of four commercial weight loss programmes in a community based sample of obese adults is commonly referred to as Diet Trials. It was designed to test the effectiveness of four of the most popular but different approaches to weight management available in the UK in a multi-centre study design. The diets tested were the Atkins diet, Rosemary Conley Diet and Fitness Plan, the Slimfast plan (a meal replacement approach) and Weight Watchers Pure Points Programme. A delayed treatment non-dieting control group was also recruited into the six month study.

  A total of a total of 293 healthy people entered the randomisation process: 79 (27%) men and 214 (73%) women with an average body mass index of 31.7 kg/m2 (range 27-38) and average age of 40.3 years (range 20-61 years).

  The results indicated that all the diets tested were effective and did produce significant weight and body fat loss compared to controls. On average men lost 9.12kg (23% of initial body fat) and women 5.2kg (16 % of initial body fat). However, there was considerable variation in weight and body fat loss within each diet group with some people doing extremely well whilst others losing very little or no weight. This led to the average differences between the diets being quite small and not significant. With regard to rate of weight loss, the Atkins diet produced the quickest initial rate of weight loss, but this rate tailed off and by the end of the six months the Atkins diet was no more or less effective in terms of absolute weight loss than the other diets tested. Gender differences are apparent with women being more successful in the assisted group programmes (Weight Watchers and Rosemary Conley) and men in the unassisted programmes (the Atkins being particularly effective in producing fat loss in men).

  Increasing fitness and activity helped in both weight and fat loss and also in ensuring the best quality of weight loss. The study population were very sedentary at baseline and although some people increased their activity and fitness over the six months many did not and gains in fitness were not just seen in the Rosemary Conley Programme (the only one with an integrated exercise component). This demonstrates that many people are aware of the benefits of increasing activity whilst trying to lose weight but will not necessarily do so.

  For blood cholesterol levels, the Atkins group performed the least well in terms of reduction of the "bad" cholesterol (LDL) but the best in maintaining "good" (HDL) cholesterol and the best in terms of fall in blood triglyceride, recognised as a beneficial outcome. Falls in LDL cholesterol, triglycerides, insulin levels and blood pressure were seen in most people who achieved weight loss. These findings demonstrates that a reduction in weight, by what ever method, brings a positive health benefit, so that after weight loss people will enjoy a decreased risk of developing heart disease or stroke.

  Diet Trials demonstrated that commercial weight loss programmes can be beneficial in weight management and provide a range of approaches and strategies that may assist people to lose weight. The differences revealed are more helpful in identifying which diet works best for individuals, and qualitative methodology (focus groups held at the University of Surrey on completing subjects) helped to identify which elements of each diet enabled people to comply to the diet for long enough for them to be successful. It also provided guidance as to the consumer experiences of these different diets. These included the recognition that the group based programmes were the most popular but the classes varied in quality with less than half the participants reported attending their classes at the end of the six month period and men in particular did not enjoy the exercise component of Rosemary Conley programme; the meal replacement approach was seen to be a simple but suitable for a short time only and the Atkins diet although viewed as restrictive was enjoyed because of the unlimited quantity of food that can be eaten and this particularly appealed to men.

  We had some nutritional concerns with the unassisted programmes mainly related to participants not complying with written information. There was a fall in fruit and vegetable consumption in both the Atkins and Slimfast diets after two months. The potential for nutritional depletion led us to instigate supplementation of the Atkins group with multi vitamins and minerals for the remainder of the dieting period.

  Diet Trials provides evidence that commercial diets could be used to help address overweight and moderate obesity in the population. However, the drop out rate overall was 28% at the end of the six months, this suggests that some approaches do not suit some people and that more information is needed to guide people as to which dietary regimen they would be most able to comply with for a long enough period to lose weight and then be able to maintain that weight loss. We made no attempt to follow-up drop outs to see what had happened to their weight at the end of the study period.

  The focus groups showed that motivation plays an important part in starting, continuing and maintaining weight control behaviours. Success was inextricably linked with a permanent change in lifestyle which included both dietary adaptation and arguably more importantly the incorporation of exercise/increased activity into everyday life. It was also recognised that "You have got to do it for yourself". These motivations were not previously observed in any of the focus groups at baseline and therefore indicate a change in attitude of this group of successful dieters. This change in attitude may be one of the key predictors of whether a dieter will be successful or not in their endeavour to achieve long term weight control.

  A follow-up after 12 months has been just been completed with 211 people invited to return to the Universities to be weighed and measured. An interesting finding from this is the behaviour of the control group, who had been given the choice of dietary programme to follow and the majority chose to attend Weight Watchers (57%), followed by Rosemary Conley, chosen by 21%, Slimfast 11% with the Atkins diet being the least popular choice. On average the control group have been as successful as those in the active diet groups with a weight loss of around one kg per month being achieved.

  There has been a significant switch of dietary programmes by the subjects after the initial six months of the study. Supported programmes (WW and RC) were the most popular choices. However, 34% reported doing their own sort of diet rather than taking part in a commercial dietary programme. There was a benefit in the medium term (12 months) in staying with some kind of formal dietary programme. Those who were still following the diet they were allocated to or who swapped to one of the diets tested had a better weight reduction after 12 months than those who were doing their own type of diet.

  If we examine only subjects who have adhered to the diet they were originally allocated to at baseline, all the diets have resulted in success with subjects reducing their initial starting weight by between 10% and 13%.


N % of baseline weight
at 12 months
% wt loss


Rosemary Conley
20 8713
Slimfast988 12
Atkins990 10
Weight Watchers2090 10



  This study has provided some evidence of the efficacy of commercial weight loss programmes over a 12 month period in free living subjects. It is the largest study carried out in the UK examining these issues to date.

  The Scientific Consortia that ran the study comprised of: Prof D J Millward, Dr L Morgan: University of Surrey, Prof M B E Livingstone: University of Ulster, Prof K Fox, University of Bristol, Prof I Macdonald: University of Nottingham, Prof A deLooy: Queen Margarets University College, Edinburgh.

  Acknowledgements: Dr S Jebb and Dr K Rennie, MRC.

  Diet Trials was funded by the BBC.



 
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