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
| 87 | 13 |
| Slimfast | 9 | 88
| 12 |
| Atkins | 9 | 90
| 10 |
| Weight Watchers | 20 | 90
| 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.
| 
