Do Lower-Carbohydrate Diets Increase Total Energy Expenditure? An Updated and Reanalyzed Meta-Analysis of 29 Controlled-Feeding Studies.
Level 1 - systematic review of randomized trials
Meta-analysis of 29 controlled-feeding studies.
PubMed 33274750 · doi:10.1093/jn/nxaa350
What was done
The authors conducted an updated systematic review and inverse-variance-weighted meta-analysis of controlled-feeding trials comparing lower- and higher-carbohydrate diets matched for energy intake or body weight, searching PubMed through March 9, 2020. They analyzed 29 trials (n = 617 participants) with intervention durations ranging from 1 to 140 days (median: 4 days) and carbohydrate differences between arms ranging from 8% to 77% of energy intake (median: 30%). Meta-regression evaluated study duration as an effect modifier, dichotomized at 2.5 weeks.
What was found
Study duration significantly modified the diet effect on total energy expenditure (TEE; P < 0.001): - In 23 shorter trials (<2.5 weeks), TEE was reduced on lower-carbohydrate diets by -50.0 kcal/d (95% CI: -77.4, -22.6 kcal/d; I² = 69.8%), or -14.5 kcal/d per 10% reduction in carbohydrate energy intake. - In 6 longer trials (≥2.5 weeks), TEE was increased on lower-carbohydrate diets by 135.4 kcal/d (95% CI: 72.0, 198.7 kcal/d; I² = 26.4%), or 50.4 kcal/d per 10% reduction in carbohydrate energy intake. Overall between-study heterogeneity was high (I² = 81.6%).
Why it matters
These findings suggest that physiological adaptation to lower-carbohydrate diets requires approximately 2 to 3 weeks, reconciling conflicting literature by showing that transient short-term reductions in energy expenditure reverse into sustained increases over longer feeding periods.
Limits
The longer-duration subgroup included only 6 trials. Overall median study duration across the 29 trials was very short (4 days). Specific baseline participant characteristics, exact macronutrient substitution details (fat vs. protein proportions), and precise measurement methods for energy expenditure were not reported in the abstract.
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- context Lowering insulin increases daily resting energy expenditure by 200 to 500 calories.