Diets that are low in refined carbohydrates may help people to keep weight off longer than low-fat plans, new research suggests.

The study in Tuesday's online issue of the Journal of the American Medical Association looked at 21 men and women with an average age of 30 who'd lost an average of nearly 14 per cent of their initial weight.

Calorie restriction is more important than diet composition for weight-loss regimens, an obesity expert says. (Mariana Bazo/Reuters)

Doctors and scientists are interested in finding the best ways to maintain weight loss knowing that just one in six overweight and obese adults in the U.S. said they were able to maintain weight loss of at least 10 per cent for a year in national surveys.

Study participants were randomly assigned to follow one of three diets:

• A low fat diet with 60 per cent of energy from high-glycemic load carbohydrates that cause a rapid rise in blood sugar like white bread, 20 per cent from fat and 20 per cent from protein, emphasizing whole grains and a variety of fruits and vegetables.
• A low glycemic index diet (40 per cent from carbohydrate, 40 per cent from fat, and 20 per cent from protein; moderate glycemic load) that replaced some processed grains and starchy vegetables with other vegetables, legumes and fruit.
• Very low carbohydrate diet modelled on Atkin's (10 per cent from carbohydrate, 60 per cent from fat, and 30 per cent from protein; low glycemic load).

The participants followed the diets in random order, each for four weeks.

The researchers found energy expenditure differed for each of the diets. Resting energy expenditure is the amount of calories the body burns at rest to breathe and to keep organs like the heart and brain working.

Decreases in resting energy expenditure was greatest for the low fat diet (loss of 205 kcal/d), intermediate for low-glycemic (166 kcal/day) and lowest for the very-low carbohydrate diet (128 kcal/d), Cara Ebbeling of Children's Hospital Boston and her co-authors said.

"The results of our study challenge the notion that a calorie is a calorie from a metabolic perspective," the researchers concluded. "Total energy expenditure differed by approximately 300 kcal/d between these two diets [very low-carbohydrate vs. low-fat], an effect corresponding with the amount of energy typically expended in one hour of moderate-intensity physical activity.

"These findings suggest that a strategy to reduce glycemic load rather than dietary fat may be advantageous for weight-loss maintenance and cardiovascular disease prevention."

Metabolic changes

Successfully maintaining weight loss requires changes in behaviour and environment to stick long-term, they noted.

Although the very low-carbohydrate diet produced the greatest metabolic improvements, it also showed potentially harmful side-effects.

The low-carbohydrate diet did the best job at preserving a participant's resting energy expenditure but cortisol levels, a hormonal measure of stress, was also highest on that diet. High cortisol levels in the long term can increase blood sugar levels and add to fat stores.

Participants weren't assessed for adherence to the diets but maintenance of weight loss was tracked.

A journal editorial accompanying the study called it a well-designed study using state-of-the-art measurements.

But interpreting the results of the short-term clinical study is challenging since one diet had 10 per cent more protein than the others and since an earlier study showed that protein produces greater increases in resting energy expenditure than fat or carbohydrate, said editorialist Dr. George Bray of Pennington Biomedical Research Centre in Baton Rouge, La.

Changing dieters' behaviour

Obesity is one of the most important and frustrating problems for physicians to treat, Bray said.

"Although the exact relationship between dietary composition and weight maintenance remains unclear, calorie restriction is more important than diet composition in administering weight-loss regimens," he concluded.

A second randomized clinical trial appearing in the same issue of the Journal of the American Medical Association that involved 363 obese and overweight adults suggested that people assigned to a standard weight-loss program lost more weight than those in a stepped up program that adjusts the frequency and intensity of treatment based on weight-loss goals.

The stepped up approach cost half as much per person ($785 versus $1,357) and by the end of the study, both groups had regained some weight.

"This trial thus shows the novel approach of spending more time and effort on patients who need it most may be more economical than implementing a standard protocol for all participants regardless of their response," Bray said.

Both studies were funded by the U.S. National Institutes of Health. Ebbeling's also received funding from the New Balance Foundation.