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Do diets work? Commercial weight loss treatments ‘on trial’!

13 May 2005

The University is committed to making the results of its research as widely available as possible. As an incentive to encourage more articles, we devised a writing competition with cash prizes. This article by Sue Baic was one of the runners-up.

Obesity affects at least 300 million people worldwide. In the UK obesity rates have trebled in the past 20 years to 20 per cent of adults and 10 per cent of children. Projections suggest that unless urgent and effective action is taken, by 2010 almost 30 per cent of UK adults and children will be obese.

Well-known complications of obesity include heart disease, high blood pressure, arthritis and type 2 diabetes. However, few people are aware of the increased risk of cancers of the breast, colon and prostate, and even less know about the associations with infertility, delayed recovery from surgery and mental health problems such as depression. Each year the cost to the UK economy is in the region of £2.5 billion from healthcare and work absence. Surprisingly, there is relatively little research on treatment of obesity, and the effectiveness of many commercial diets is unknown. Despite this, in the UK last year 34 million people tried to lose weight, spending £10 billion on commercial diets in the process.

Our study, the first of its kind in the UK, was to to test the efficacy of the most popular commercial weight-loss programmes in obese adults. An additional aspect was that a sample of the participants and the researchers were filmed for Diet Trials – a 14-part BBC TV series. Two hundred and ninety three obese adults (27 per cent men and 73 per cent women) were recruited via BBC TV adverts. Over 4,000 people volunteered. The study was carried out in five centres, including Bristol, with roughly equal numbers in each centre. Participants were randomly allocated to one of four diets, or a control group.

“Almost all countries in the world are facing an obesity epidemic” WHO (2003)

For each participant we took a series of measures at the beginning and at monthly intervals over a six-month period. These included weight loss, percentage of fat loss and blood tests, particularly reflecting risk of heart disease and diabetes. Fitness levels were measured using an aerobic adaptation test on a bicycle. In order to develop a better understanding of how to support commercial diets, ten volunteers contributed two interviews during the trial to help inform on their personal experiences.

Two hundred and ten participants completed the six-month study. Although 28 per cent withdrew over the course of the study, there were no differences in drop-out rates between the diet groups. At the end of the trial significant amounts of weight and body fat had been lost in all diet groups, compared with controls – over 300kg were lost in the Bristol group alone. Average weight loss was in the region of ten per cent body weight, 78 per cent of which was body fat. Participants on the Atkins diet lost weight the most rapidly, but this levelled off after three months. By six months there was no difference between the diet groups. Fitness levels increased in some members within each group and was associated with an extra three to five kilograms of total weight loss and a greater percentage of fat loss.

Over 300kg were lost in the Bristol group alone

Generally blood test profiles showed improvements with weight loss, indicating lower risks of heart disease and diabetes. The Atkins diet had the least effect on lowering blood cholesterol levels. Atkins dieters liked the simple and novel approach at first, but when their diets were examined at two months they revealed worryingly low intakes of fruit and vegetables. As a result we had to commence vitamin supplements and promote potassium intake. The Atkins diet was also significantly more restrictive and expensive than the other diets. Slimfast meal replacements were found to be simple and convenient but participants on the milkshakes reported difficulties with missing solid food and joining in family meals. This made it more suitable for short-term or occasional use.

Both of the ‘group’ approaches – Rosemary Conley and Weight Watchers – were well liked for being easy to follow, and for fitting in with family life. They also allowed plenty of natural and normal foods and treats and offered support and monitoring of progress. The exercise aspect of the Rosemary Conley Health and Fitness plan was particularly enjoyed.

Commercial weight-loss treatments are effective in producing weight loss in individuals who adhere to them. Weight loss reduces the risk from chronic health problems, reflected in a range of blood tests. Increasing physical activity and fitness levels at the same time can improve both weight and fat loss. Interviews confirmed that these outcomes were achieved when dieters received close, regular and genuine support of experts who knew them. The lack of weight loss in the control group confirms that this attention made a profound contribution to the success of these diets.

Different commercial diets seem to suit different people according to their lifestyle, eating patterns and their need for support and monitoring. Offering a range of approaches seems to be most useful in helping to treat obesity. Presenting the results of the study as a TV series was a novel way to deliver an important public health message. Furthermore, TV coverage illustrated the daily battle many dieters face, the advantages of different approaches and the health benefits of weight loss. We were able to reach an audience of four to six million viewers per episode. After the show 25,000 informative support packs were sent out.


                            The diets

                                         Weight Watchers Pure Points

Participants attended weekly group meetings and, using a points system, followed a diet that limited their sugars and saturated fat intake.

Rosemary Conley Health and Fitness

Participants followed a low-fat diet and went to weekly meetings incorporating an exercise class.

Slimfast Meal Replacement Plan

Meal replacements – milk shakes or soups – were used for two meals a day, together with a calorie-counted evening meal.

                                          Atkins Diet

A low-carbohydrate diet was followed where cereals were avoided and fruit and vegetables restricted, but fat and protein were freely allowed.

                                          Control group

Participants were asked to carry on as normal during the initial six months of the trial. On completion they were offered a six-month funded diet of their choice.

Sue Baic/Department of Exercise and Health Sciences

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