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NASHVILLE -- A low carbohydrate diet increased energy expenditure during weight maintenance, researchers reported here.

In a group of overweight adults who recently lost 12% of their body weight, a low carb diet helped burn more calories during the weight maintenance phase, according to David Ludwig, MD, PhD, of Boston Children's Hospital in Massachusetts, and colleagues.

Specifically looking at the total energy intake, every 10% decrease in the amount of carbs that made up the person's total energy intake was tied to 52 more kcal burned each day (95% CI 23-82 kcal/day), they reported at Obesity Week, a joint meeting of The Obesity Society and the American Society for Metabolic & Bariatric Surgery. The results were simultaneously published in.

Compared with individuals placed on a high carb diet during the weight maintenance phase, those on a low carb diet had a 209 kcal/day (95% CI 91 to 326 kcal/day) greater change in total energy expenditure. Even those on a moderate carb diet saw a 91 kcal/day (95% CI -29 to 210 kcal/day) greater change in total energy expenditure compared with those on a high carb diet, the authors stated.

These outcomes were "almost exactly as previously hypothesized," Ludwig told MedPage Today, adding that "these results indicated that the type of calories consumed may influence the number of calories burned independently of body weight, with potential relevance to the long-term success of weight loss treatment."

"Conventional teaching in nutrition holds that all calories are metabolically alike to the body," he explained. "This view is based predominantly on short-term feeding studies, typically less than 2 weeks. However, the process of adapting to a low carbohydrate diet, [high fat] takes at least 2 to 3 weeks, which could confound the data. We designed our study to examine diets under the rigorous control of a feeding study, with sufficient duration -- 20 weeks -- to see chronic effects."

The randomized trial followed 234 adults (ages 18-65) with a BMI of 25 prior to weight loss. Before the 12-week run-in weight loss phase of the trial, all participants were placed on the same diet comprised of 45% carbohydrate, 30% fat, and 25% protein. After a 12% (+2%/-2%) weight loss during this period, 164 adults were then randomized to a high, moderate, or low carb diet for 20 weeks:

• High carb diet: 60% carb/20% fat/20% protein
• Moderate carb diet: 40% carb/40% fat/20% protein
• Low carb diet: 20% carb/60% fat/20% protein

In a separate per-protocol analysis, which excluded 42 individuals who did not maintenance weight loss within 2 kg (4.4 lbs) of the their weight at the start of the 20-week randomization phase, similar trends were seen among each of the three diets.

Among those on a low carb diet, ghrelin and leptin were both significantly lower compared with those on a high carbohydrate diet. As for individuals who fell into the highest third of insulin secretion prior to weight loss, measured 30 minutes after oral glucose, the differences between total energy expenditure was even greater between those on a low versus high carb diet:

• Full analysis: 308 kcal/day more expenditure for low carb dieters (95% CI 101-514)
• Per-protocol analysis: 478 kcal/day (95% CI 232-724)

In terms of physical activity, the authors reported that "resting energy expenditure, total physical activity, and moderate to vigorous intensity physical activity were marginally higher in the group assigned to the low carbohydrate diet (group differences or linear trends of borderline significance)."

"This study needs to be replicated before the findings can be fully embraced," explained Ludwig. "If this effect can be substantiated among a broader population with excessive weight, it would produce about a 20 pound weight loss in a few years, without reducing calorie intake. Our study is broadly consistent with other lines of investigation suggesting benefits of a low glycemic load diet for diabetes and heart disease prevention. However, clinical translation of our data must await additional research."

Study limitations included potential measurement error and non-compliance.

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