Effects of carbohydrate quantity and glycemic index on resting metabolic rate and body composition during weight loss

Abstract

Objective: To examine the effects of diets varying in carbohydrate and glycemic index (GI) on changes in body composition, resting metabolic rate (RMR), and metabolic adaptation during and after weight loss.

Methods: Adults with obesity (n = 91) were randomized to one of four provided-food diets for 17 weeks. Diets differed in percentage energy from carbohydrate (55% or 70%) and GI (low or high) but were matched for protein, fiber, and energy. Body weight, body composition, RMR, and metabolic adaptation (measured RMR-predicted RMR) were measured during weight loss and subsequent weight stability.

Results: No effect of dietary carbohydrate content or GI on body weight loss or percentage of weight lost as fat mass (FM) was observed. Measured RMR was significantly lower (-226 kJ/day [95% CI: -314 to -138 kJ/day], P < 0.001) than predicted RMR following weight loss, but this difference was attenuated after 5 weeks of weight stability. Metabolic adaptation did not differ by dietary carbohydrate content or GI and was not associated with weight regain 12 months later.

Conclusions: Moderate-carbohydrate and low-GI diets did not preferentially reduce FM, preserve lean mass, or attenuate metabolic adaptation during weight loss compared to high-carbohydrate and high-GI diets.

Figure 1

CONSORT diagram and study design. GI, glycemic index; HighCarb, 70% energy from carbohydrate; ModCarb, 55% energy from carbohydrate.

Figure 2

A) Weight loss and B) percentage of total weight loss attributable to fat mass and fat free mass while consuming provided-food diets differing in glycemic index (GI), and percent energy from carbohydrate (55%, ModCarb and 70%, HighCarb) for 17 wk (n = 79). Values are mean ± SEM. Weight loss analyzed by repeated measures ANCOVA, body composition by 2-factor ANOVA. ^a,bMain effect of time; ^asignificant decrease from baseline (P < 0.001), ^bsignificant difference from Phase 2 end (P < 0.001). No diet effects (main effects or interactions) for any comparisons.

Figure 3

Measured versus predicted resting metabolic rate (RMR) at the end of A) Phase 2 and B) Phase 3 (n = 77; Pearson’s correlations). Solid line, measured = predicted; dashed line, regression line between measured and predicted. GI, glycemic index; HighCarb, 70% energy from carbohydrate; ModCarb, 55% energy from carbohydrate.

Figure 4

Adaptation of resting metabolic rate (RMR) and subsequent 12-mo weight change (n = 60). A) Association between RMR adaptation measured at the end of Phase 3 and subsequent 12-mo weight change during Phase 4 (Pearson’s correlation). B) RMR adaptation by tertile of weight regain during Phase 4. Differences between tertiles were not statistically significant; 1-way ANOVA, P = 0.77. Bars are mean – SEM. Glycemic index (GI); HighCarb, 70% energy from carbohydrate; ModCarb, 55% energy from carbohydrate.