It is estimated that most adults in the UK and the US will undertake a diet at some time, but long-term success rates are reported to be poor with half of the weight lost being regained within one year.
A recent report from the House of Commons Health Committee stated that "obesity has grown by 400 per cent in the last 25 years" in the UK.
The market for commercial diets is estimated to be worth about £11bn (€16bn) by 2007 in the UK, with speciality products, functional foods, and meal replacers taking centre stage.
A new article in the British Medical Journal (Vol. 332, pp. 1309-1314) compared the effects of four commercial diets - Dr. Atkins' new diet revolution, Slim-Fast plan, Weight Watchers pure points programme, and Rosemary Conley's eat yourself slim diet and fitness plan.
The researchers, based at five different centres around the UK, recruited 240 mildly obese 40-year old volunteers following one of the four commercial weight loss programmes. A further 60 volunteers with similar characteristics were recruited to eat their normal diet and act as a control for the others.
No standardisation of energy intake was attempted so that the study was a reflection of the volunteers' interpretation of the diet programmes.
After six months, the results indicated that all four programmes resulted in similar weight loss (5.9 kg), fat loss (4.4 kg), and a reduction in waist circumference (7 cm).
The researchers also measured total cholesterol levels every two months, and found that in all groups except the Atkins group experienced a small but significant drop in total cholesterol levels. After six months, only the Weight Watchers group had sustained reduced cholesterol levels (0.55 millimoles per litre).
"The Atkins diet had no detrimental effects on total cholesterol concentrations or renal functions, although the overall safety of the diet was not tested," stressed lead researcher Helen Truby from the University of Surrey.
Rachel Cooke from the British Dietetic Association told NutraIngredients.com that the diets worked merely by lowering the calorie intake overall.
However, "from a dietetic perspective emphasis should continue to be on consistent messages [about] healthy lifestyle, which includes healthy eating and healthy activity," said Clarke.
The Weight Watchers and Rosemary Conley diet are based around the general healthy eating guidelines, said Cooke, while the Slim-Fast plan is based around replacement of two meals and a normal third meal, also based on the principles of healthy eating.
"The Atkins diet was high protein and low carbohydrates and fruit/veg [and] this was the only diet that did not base itself around healthy eating principles and went against the 5-A-DAY message for health," she said.
Clarke said the Atkins diet, which reported higher initial weight loss within the first eight weeks of dieting compared to the other diets, might be " used as a way of kick starting an individual weight loss."
Both the study authors and Clarke noted the study results highlight the need for achievable weight loss targets. Many dieters have unrealistic targets, said Truby.
"A healthy weight loss is 1-2lb per week and Jung identified a 10 per cent reduction in weight has significant benefits to long term health - often one of the problems is that one or both parties involved in weight loss are looking at unrealistic expectations for both short term goals and identified weight loss targets," said Cooke.