The study, partly funded by the Agricultural Research Service (ARS)- the US Department of Agriculture's (USDA) scientific research arm- compared four popular diet plans over a one-year period.
The diets chosen included the Atkins (carbohydrate restriction), Ornish (fat restriction), Weight Watchers (calorie and portion size restriction), and Zone (high-glycemic-load carbohydrate restriction and increased protein) diets.
Researchers from the Lipid Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University and Tufts-New England Medical Center in Boston randomly assigned 160 overweight or obese volunteers to one of the four diet plans.
The participants in each diet plan were representative of the overweight population in the US, in terms of age, race, sex, body mass index and metabolic characteristics.
Published in this month's issue of the Agricultural Research magazine, the results revealed that all four diets led to "modest but significant" weight loss, and a 10 percent improvement in the balance of 'good' HDL and 'bad' LDL cholesterol levels.
However, these results were only observed in those participants who completed the full period of dieting. And when it came to what the researchers termed the more "extreme" diet plans- Atkins and Ornish- only half of the volunteers stuck to these for the full year. In contrast, almost two-thirds were able to complete the more "moderate" diet plans- Weight watchers and Zone.
"The study showed that whether volunteers restricted carbohydrate calories or fat calories-whether they lowered intake overall, or balanced intake overall-everybody lost weight," said researcher Ernst Schaefer.
"Ultimately, it comes down to calorie restriction. The strongest predictor of weight loss was not the type of diet, but compliance with the diet plan that subjects were given."
The findings, which were previously published in the Journal of the American Medical Association, support the belief that calorie-restriction diets must not come into conflict with a person's preferred foods.
"Implementing a dietary regimen that can transition an individual into a healthful eating pattern after the diet ends is also very important," said ARS human nutrition national program leader Molly Kretsch. "Lifestyle practices that help people maintain a healthy body weight, incorporate the right balance of foods and appropriate portion sizes, and increase their physical activity are the keys to long-term weight management."
Participants in the study who improved their cholesterol ratios by 10 percent improved their heart disease risk factors by 20 percent. And according to the researchers, for every one percent of weight loss a dieter achieves, there will be a two percent, or twice as much, reduction in heart disease risk factors.
In addition, all four diet plans promoted lower blood insulin levels as well as lower levels of C reactive protein (CRP). High levels of CRP in the blood have been linked to heart disease.