Calorie Restriction Increases Muscle Mitochondrial Biogenesis in Healthy Humans

TLDR

Caloric restriction without malnutrition extends lifespan across species and reduces mitochondrial free‑radical production, yet the underlying mechanisms remain poorly understood. This study aimed to determine how caloric restriction alone or combined with exercise affects muscle mitochondrial bioenergetics in young overweight adults. Thirty‑six participants were randomized to a 6‑month intervention of control (100 % energy), caloric restriction (25 % reduction), or caloric restriction plus exercise (12.5 % restriction plus 12.5 % increased energy expenditure). Compared with controls, caloric restriction—alone or with exercise—reduced 24‑hour energy expenditure, upregulated mitochondrial genes (PPARGC1A, TFAM, eNOS, SIRT1, PARL), increased mitochondrial DNA content by 35 % and 21 % respectively, lowered DNA damage, but did not alter key mitochondrial enzyme activities, indicating that caloric restriction enhances mitochondrial biogenesis and function while decreasing whole‑body oxygen consumption.

Abstract

Background Caloric restriction without malnutrition extends life span in a range of organisms including insects and mammals and lowers free radical production by the mitochondria. However, the mechanism responsible for this adaptation are poorly understood. Methods and Findings The current study was undertaken to examine muscle mitochondrial bioenergetics in response to caloric restriction alone or in combination with exercise in 36 young (36.8 ± 1.0 y), overweight (body mass index, 27.8 ± 0.7 kg/m2) individuals randomized into one of three groups for a 6-mo intervention: Control, 100% of energy requirements; CR, 25% caloric restriction; and CREX, caloric restriction with exercise (CREX), 12.5% CR + 12.5% increased energy expenditure (EE). In the controls, 24-h EE was unchanged, but in CR and CREX it was significantly reduced from baseline even after adjustment for the loss of metabolic mass (CR, −135 ± 42 kcal/d, p = 0.002 and CREX, −117 ± 52 kcal/d, p = 0.008). Participants in the CR and CREX groups had increased expression of genes encoding proteins involved in mitochondrial function such as PPARGC1A, TFAM, eNOS, SIRT1, and PARL (all, p < 0.05). In parallel, mitochondrial DNA content increased by 35% ± 5% in the CR group (p = 0.005) and 21% ± 4% in the CREX group (p < 0.004), with no change in the control group (2% ± 2%). However, the activity of key mitochondrial enzymes of the TCA (tricarboxylic acid) cycle (citrate synthase), beta-oxidation (beta-hydroxyacyl-CoA dehydrogenase), and electron transport chain (cytochrome C oxidase II) was unchanged. DNA damage was reduced from baseline in the CR (−0.56 ± 0.11 arbitrary units, p = 0.003) and CREX (−0.45 ± 0.12 arbitrary units, p = 0.011), but not in the controls. In primary cultures of human myotubes, a nitric oxide donor (mimicking eNOS signaling) induced mitochondrial biogenesis but failed to induce SIRT1 protein expression, suggesting that additional factors may regulate SIRT1 content during CR. Conclusions The observed increase in muscle mitochondrial DNA in association with a decrease in whole body oxygen consumption and DNA damage suggests that caloric restriction improves mitochondrial function in young non-obese adults.