Dietary carbohydrate and energy expenditure: Exploring biological mechanisms of body-weight control

A meta-analysis of 29 controlled-feeding studies sheds new light on the relation between macronutrient composition and total energy expenditure, according to a recent study published in The Journal of Nutrition.

The concept of energy balance and body weight regulation states that when energy intake is greater than energy expenditure excess calories are stored in the body with a subsequent increase in body weight. In this view, diets of equal caloric value but having differing ranges of macronutrient composition from very-low-carbohydrate to very-low fat should yield similar physiological impact.  However, how the body uses calories is not that simple according to lead author David Ludwig (Harvard Medical School) and coauthors, which may account for divergent findings among studies.

The effect of macronutrient composition on total energy expenditure remains controversial, according to the study authors. “One possible explanation for this inconsistency may be study duration as a physiological adaptation to lower carbohydrate intake may require 2 to 3 weeks.”

To test the hypothesis that the effects of carbohydrates, expressed as a percent of energy intake on total energy expenditure vary with time, study results from a previous meta-analysis and those identified in new trials were analyzed. The duration of the studies, which included 617 participants, ranged from 1 to 140 days, with the difference in carbohydrate intake from 8% to 77%.

Among the 23 shorter trials (< 2.5 weeks), total energy expenditure was slightly reduced on lower-carbohydrate diets. In contrast, the longer duration lower-carbohydrate diet substantially increased total energy expenditure.  It was estimated that these diets increased energy expenditure by ∼50 kcal per day for every 10% decrease in carbohydrates (expressed as % energy intake).

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A corresponding editorial provides further perspective regarding the optimal diet composition for body-weight control. Researchers Faidon Magkos and Arne Astrup (University of Copenhagen) stress the importance of experimental testing in humans to better understand the metabolic nuances and interrelations between diet composition, metabolic fuel availability, body composition, and energy expenditure at various stages of the natural course of obesity.

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