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BOSTON, MASSACHUSETTS. Increasing numbers of people are turning to well-known diets both to control
weight and to protect their health. These diets vary widely in their recommendations and many diverge from
accepted medical guidance, nevertheless they are heavily promoted by the media and a number of medical
experts. Good-quality comparative data on the safety and effectiveness of these diets is lacking, so
researchers from Boston's Tufts-New England Medical Center undertook a randomized trial of four popular
diets: Weight Watchers, which stresses reduced calories; Atkins, which focuses on reduced carbohydrate
intake; the Zone diet, which stresses glycemic load and nutritional balance; and the low-fat vegetarian plan
devised by Dr Dean Ornish.
They randomly assigned 40 overweight or obese adults with cardiac risk factors (hypertension, dyslipidemia, or fasting hyperglycemia) to each of the diet plans for a year. Participants were given copies of books that detailed each plan and provided with group-based advice from a dietician and physician during the first two months. Overall adherence rates were low - after two months, fewer than 80 per cent remained on the diets, and after a year, the figure dropped to 25 per cent. Participants who adhered to the diet in each group lost similar amounts of weight, slightly less than 4 per cent of body weight at two months, with 10 per cent of each group losing more than 10 per cent of their weight at one year. Higher weight loss was shown by those who adhered closely, but diet type was not linked to weight loss. Coronary risk factors were reduced by each diet in proportion to weight loss. Insulin and C-reactive protein were significantly lowered, and LDL/HDL cholesterol ratio was reduced by around 10 per cent in participants who completed the diets, again regardless of diet type.
In an accompanying commentary, an expert from the University of Colorado at Denver writes that the study
had the potential to determine which diet works best, but adherence was low and no differences were
observed between the diets. He supports individually-tailored diet plans, alongside increased physical
activity.
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