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Different Diets, Different Outcomes continued...

The study participants ate about 1,600 calories a day on each of the diets and the amount of calories burned was measured using state-of-the-art methods.

The testing confirms that they burned about 300 calories more a day when following the very-low-carb eating plan compared to the low-fat plan, and about 150 calories more on the low-glycemic index diet compared to the low-fat plan.

"The best diet from a metabolic perspective was the low-carbohydrate diet, but there were downsides," Ludwig says.

Stress Hormone Levels Higher in Low-Carb Eaters

Levels of the stress hormone cortisol and C-reactive protein -- an indicator of inflammation in the body -- were higher during the low-carb phase of the study.

"The metabolic benefits of this diet may be undermined by more inflammation and higher cortisol, both of which can increase [heart disease and stroke] risk over time," Ludwig says.

Nutritionist Elisabetta Politi, MPH, calls the study intriguing and deserving of further research. Politi is the nutrition director of the Duke Diet and Fitness Center in Durham, N.C.

"The idea that the type of calories people take in has a direct impact on the amount of energy they expend is certainly intriguing and worth exploring further," she tells WebMD.

She says since the participants were only followed for the three months that they followed the highly controlled eating plans, it is not clear if one diet really is better than another for maintaining weight loss.

"It makes sense that people would be able to stick with a low-glycemic-index diet better because it is less restrictive, but that wasn't really shown in this study," she says.

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