There is an ongoing debate about what types of diet are most effective for treating overweight people and in the food industry this has had an impact on products, particularly in the aftermath of the low-carb Atkins phenomenon.
Many popular diets emphasize degrees of carbohydrate, protein or fat. However, researchers at the Harvard School of Public Health (HSPH) and Pennington Biomedical Research Center of the Louisiana State University System, said there have been few studies lasting more than a year that evaluate the effect on weight loss of diets with different compositions of those nutrients.
Now they have published the results of a two-year study in The New England Journal of Medicine which shows that it makes no difference.
Instead it found that reduced-calorie diets result in clinically meaningful weight loss “regardless of which macronutrients they emphasize”.
It said: “Diets that are successful in causing weight loss can emphasize a range of fat, protein, and carbohydrate compositions that have beneficial effects on risk factors for cardiovascular disease and diabetes.
“Such diets can also be tailored to individual patients on the basis of their personal and cultural preferences and may therefore have the best chance for long-term success.”
Many paths towards weight-loss
Elizabeth Nabel, director of the National Heart, Lung, and Blood Institute, which funded the research, said: “These results show that, as long as people follow a heart-healthy, reduced-calorie diet, there is more than one nutritional approach to achieving and maintaining a healthy weight.”
The study also showed that participants who regularly attended counselling sessions lost more weight than those who didn't.
Frank Sacks, professor of cardiovascular disease prevention at HSPH and lead author, said: "These findings suggest that continued contact with participants to help them achieve their goals may be more important than the macronutrient composition of their diets."
The diets
The research involved overweight participants (62 per cent women, 38 per cent men) from diverse backgrounds who were assigned to four different diets: Low-fat, average protein, Low-fat, high-protein, High-fat, average protein and High-fat, high-protein.
All the diets followed heart-healthy principles, replacing saturated with unsaturated fat and were high in whole cereal grains, fruits and vegetables, with a 750-calorie reduction per day.
Participants were also asked to do 90 minutes of moderate exercise each week, record their daily food and drink intake and attend counselling.
The results showed that regardless of diet, weight loss and reduction in waist circumference were similar.
Participants lost an average of 13 pounds at six months and maintained a 9-pound loss at two years with an average of two inches off the waist.
Most risk factors for cardiovascular disease improved for dieters. HDL, so-called good cholesterol, increased and LDL, or bad cholesterol, along with triglycerides, blood pressure and insulin decreased.
The metabolic syndrome, a group of coronary heart disease risk factors including high blood pressure, insulin resistance and abdominal obesity, also decreased.
Source: The New England Journal of Medicine 26 February 2009, Volume 360, Number 9, Pages 859-873"Randomized Trial Comparing Fat, Protein, and Carbohydrate Composition of Diets for Weight Loss for Two Years” Authors: F.M. Sacks, G.A. Bray, V.J. Carey, S.R. Smith, et al.