The study, published in the Journal of the American Medical Association, may see a revival in low carbohydrate, high protein/fat diets that have lost popularity amongst the public with critics saying that the approach puts followers at a higher risk of clogged arteries and heart attack in the long-term.
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.
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.
Researchers from Stanford University Medical School assigned 311 premenopausal overweight and obese women (average age 41, average BMI 32 kg per sq. m) to follow one of four diets - Atkins (very low in carbohydrate), Zone (low in carbohydrate), Ornish (high in carbohydrate) and LEARN (low in fat, high in carbohydrate, based on national guidelines) - for one year.
The women received attended one-hour classes by registered dieticians once a week for eight weeks, and were responsible for preparing and buying all their own meals, and not everyone followed the diets exactly as the books described, just as in real life.
The study, funded by the National Institutes of Health and the Community Foundation of South-eastern Michigan, found that weight loss was highest in the women following the Atkins diet (4.7 kg, 10.4 lbs) compared to the Zone (1.6 kg, 3.5 lbs), LEARN (2.2 kg, 5.7 lbs), and Ornish (2.6 kg, 4.8 lbs).
"Compared with women who were assigned to follow diets having higher carbohydrate content, women assigned to the diet with the lowest carbohydrate content had more weight loss and more favourable changes in related metabolic risk factors at two and six months," wrote lead author Christopher Gardner in JAMA.
Despite previous concerns over low carbohydrate diets adversely affecting blood lipid profiles, the current study did not report any such adverse effects.
Moreover, the two per cent increase in LDL-cholesterol levels and 30 per cent increase in triglyceride levels after two months of following the Atkins diet were "consistent with a beneficial increase in LDL particle size," said the researchers, "although LDL particle size was not assessed in our study."
The researchers stated that these results suggest that there were no adverse effects on the lipid profiles of the premenopausal women.
"Concerns about adverse metabolic effects of the Atkins diet were not substantiated within the 12-month study period. It could not be determined whether the benefits were attributable specifically to the low carbohydrate intake vs. other aspects of the diet (e.g., high protein intake)," wrote Gardner.
"While questions remain about long-term effects and mechanisms, these findings have important implications for clinical practice and health care policy. Physicians whose patients initiate a low-carbohydrate diet can be reassured that weight loss is likely to be at least as large as for any other dietary pattern and that the lipid effects are unlikely to be of immediate concern. As with any diet, physicians should caution patients that long-term success requires permanent alterations in energy intake and energy expenditure, regardless of macronutrient content," concluded the authors.
Over 300m adults are obese worldwide, according to latest statistics from the WHO and the International Obesity Task Force. About one-quarter of the US adult population is said to be obese, with rates in Western Europe on the rise although not yet at similar levels.
Source: Journal of the American Medical Association
7 March 2007, Volume 297, Pages 969-977
"Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women"
Authors: C.D. Gardner, A. Kiazand, S. Alhassan, S. Kim, R.S. Stafford, R.R. Balise, H.C. Kraemer, A.B. King