Background: Because most studies of weight loss diets are hampered by small numbers of participants and short duration, little is known about which types of diets are most effective. One meta-analysis has suggested relative equivalence between low-carbohydrate diets that do not limit energy intake and diets that are low in fat and high in carbohydrates. Gardner and colleagues evaluated the effects of four diets on weight loss: the Atkins (lowest carbohydrate); the Zone (low carbohydrate); LEARN (Lifestyle, Exercise, Attitudes, Relationships, and Nutrition; low fat, high carbohydrate), and Ornish (highest carbohydrate).
The Study: The study included community-dwelling premenopausal women 25 to 50 years of age with a body mass index between 27 and 40 kg per m2. Patients with chronic illnesses were excluded, except for those with well-controlled hypertension or hypercholesterolemia.
Participants were randomly selected to receive a book about one of the four diets, and all groups received dietary advice taught one hour per week for eight weeks. Each group was given target fat and carbohydrate limits, depending on the dietary assignment. Behavior modification was incorporated in the LEARN and Atkins diet groups but did not play a major role in the other groups. After baseline evaluation, patients were followed at two, six, and 12 months. They were assessed periodically with unannounced dietary recall surveys. In addition, at each benchmark evaluation, patients were weighed and lipid and blood pressure measurements were taken.
|Diet||Weight loss||95% confidence interval|
|Atkins||10 lb, 6oz (4.7 kg)||13 lb, 14 oz to 6 lb, 13 oz(6.3 to 3.1 kg)|
|LEARN||4 lb, 14 oz (2.2 kg)||7 lb, 15 oz to 1 lb, 12 oz(3.6 to 0.8 kg)|
|Ornish||5 lb, 12 oz (2.6 kg)||8 lb, 6 oz to 2 lb, 14 oz(3.8 to 1.3 kg)|
|Zone||3 lb, 8 oz (1.6 kg)||6 lb, 3 oz to 14 oz (2.8 to 0.4 kg)|
Results: Class attendance was at least 75 percent, and the study retention rate was similar among groups. Caloric intake decreased in all diet groups and was documented at each benchmark visit. Weight loss was greatest in the Atkins group compared with the other diet groups; however, the only statistically significant difference in weight change was between the Atkins and Zone diets (see accompanying table). Compared with the other groups, the Atkins group had a statistically greater change in weight at two and six months and in high-density lipoprotein cholesterol at all benchmark visits.
Conclusion: The authors conclude that patients on the Atkins diet have greater weight loss at two and six months than those on the Zone, Ornish, or LEARN diets and have greater weight loss at one year than those on the Zone diet. Atkins dieters also have more favorable lipid profiles and blood pressures at various measurements, suggesting that concerns about how low-carbohydrate diets affect cardiac risk factors are unfounded.