Vitamin C depletion reduces fat oxidation at rest in obese adults consuming a calorie‐restricted diet

Epidemiologic data suggest an inverse relationship between vitamin C nutriture and body weight. We investigated the impact of vitamin C status on weight loss and on fat oxidation at rest as indicated by the respiratory exchange ratio (RER). Utilizing a double‐blind, placebo‐controlled study design, obese subjects consumed a low‐vitamin C (<40 mg/d), low‐fat, calorie‐restricted diet for 8 weeks. At the start of the trial, subjects were stratified by gender and body mass index and randomly assigned to groups: placebo (CON; n=10) or vitamin C (VC; 500 mg/d; n=10). Total body mass was recorded weekly; fat mass (determined by bioelectrical impedance), resting metabolic rate, RER, and plasma vitamin C were measured at weeks 0, 4, and 8. Preliminary data through trial week 4 are reported herein. After 4 weeks of diet adherence, plasma vitamin C concentrations increased in VC (0.841±0.034 and 1.089±0.148 mg/dL for weeks 0 and 4, respectively) and decreased in CON (0.732±0.108 and 0.538±0.117 mg/dL) (p<0.001 for time x group effect). Body mass was reduced significantly (p<0.001, time effect only): −4.1 and −4.3 kg in VC and CON, respectively. Body fat mass decreased in both groups, but this reduction approached significance only for VC (‐1.7 kg; p=0.077). RER was not altered significantly between trial weeks 0 and 4 in VC (0.765±0.055 and 0.783±0.054; p=0.622); however, RER increased significantly in CON (0.756±0.085 and 0.837±0.078; p=0.018) indicating reduced fat oxidation over time. These preliminary data suggest that vitamin C depletion reduces fat oxidation at rest in obese individuals on a calorie‐restricted diet, but vitamin C depletion does not appear to affect weight loss potential. This research was supported by a grant from the General Mills, Bell Institute of Health and Nutrition.