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Several popular diets confer similar benefits, with best results from strict adherence

A new study challenges the idea that one type of diet is best for everybody, and that very low carbohydrate diets are better than standard diets. The study found that several popular diets resulted in similar weight loss and reduction of several cardiac risk factors over a 1-year period, and that dietary adherence, not type of diet, was the key to success.

The diets studied were Weight Watchers, which recommends restriction of portion sizes and calories; the Atkins diet, which minimizes carbohydrate intake without fat restriction; the Zone diet, which modulates the balance of macronutrients (proteins, carbohydrates, and fats) and glycemic load (carbohydrate-induced blood sugar level); and the Ornish diet, which restricts fat.

In the study, which was supported in part by the Agency for Healthcare Research and Quality (T32 HS00060), researchers led by Michael L. Dansinger, M.D., of Tufts-New England Medical Center, randomized 160 adults aged 22 to 72 years to the four popular diet groups. The adults were overweight or obese and had several risk factors for cardiac problems: high blood pressure, high cholesterol, and fasting hyperglycemia (high blood-sugar levels). The researchers assessed subjects' weight loss and change in these and other cardiac risk factors at baseline and at 2, 6, and 12 months.

Participants were more likely to drop out of the study with more extreme diets (Atkins and Ornish) than the moderate diets (Zone and Weight Watchers). Among those who completed the study, mean weight loss at 1 year was 2.1 kg (4.6 lbs) for Atkins, 3.2 kg (7 lbs) for Zone, 3.0 kg (6.6 lbs) for Weight Watchers, and 3.3 kg (7.3 lbs) for Ornish.

Each diet significantly reduced the low-density lipoprotein/high-density lipoprotein (HDL) cholesterol ratio by about 10 percent but had no significant effect on blood pressure or glucose levels at 1 year. For each diet, decreasing levels of total/HDL cholesterol, C-reactive protein, and insulin were significantly associated with weight loss, with no significant difference between diets. The amount of weight lost was associated with self-reported dietary adherence level but not with diet type.

See "Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease reduction," by Dr. Dansinger, Joi Augustin Gleason, M.S., R.D., John L. Griffith, Ph.D., and others, in the January 5, 2005, Journal of the American Medical Association 293(1), pp. 43-53.

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