ClinicalTrials.gov Identifier: NCT00099151.

BackgroundCaloric 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 FindingsThe 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.ConclusionsThe 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.

Calorie restriction (CR) extends life span and retards age-related chronic diseases in a variety of species, including rats, mice, fish, flies, worms, and yeast. The mechanism or mechanisms through which this occurs are unclear. CR reduces metabolic rate and oxidative stress, improves insulin sensitivity, and alters neuroendocrine and sympathetic nervous system function in animals. Whether prolonged CR increases life span (or improves biomarkers of aging) in humans is unknown. In experiments of nature, humans have been subjected to periods of nonvolitional partial starvation. However, the diets in almost all of these cases have been of poor quality. The absence of adequate information on the effects of good-quality, calorie-restricted diets in nonobese humans reflects the difficulties involved in conducting long-term studies in an environment so conducive to overfeeding. Such studies in free-living persons also raise ethical and methodologic issues. Future studies in nonobese humans should focus on the effects of prolonged CR on metabolic rate, on neuroendocrine adaptations, on diverse biomarkers of aging, and on predictors of chronic age-related diseases.

THE PENNINGTON CALERIE TEAMOBJECTIVE -The purpose of this article was to determine the relationships among total body fat, visceral adipose tissue (VAT), fat cell size (FCS), ectopic fat deposition in liver (intrahepatic lipid [IHL]) and muscle (intramyocellular lipid [IMCL]), and insulin sensitivity index (S i ) in healthy overweight, glucose-tolerant subjects and the effects of calorie restriction by diet alone or in conjunction with exercise on these variables. RESEARCH DESIGN AND METHODS-Forty-eight overweight volunteers were randomly assigned to four groups: control (100% of energy requirements), 25% calorie restriction (CR), 12.5% calorie restriction ϩ12.5% energy expenditure through structured exercise (CREX), or 15% weight loss by a low-calorie diet followed by weight maintenance for 6 months (LCD). Weight, percent body fat, VAT, IMCL, IHL, FCS, and S i were assessed at baseline and month 6. RESULTS -At baseline, FCS was related to VAT and IHL (P Ͻ 0.05) but not to IMCL. FCS was also the strongest determinant of S i (P Ͻ 0.01). Weight loss at month 6 was 1 Ϯ 1% (control, mean Ϯ SE), 10 Ϯ 1% (CR), 10 Ϯ 1% (CREX), and 14 Ϯ 1% (LCD). VAT, FCS, percent body fat, and IHL were reduced in the three intervention groups (P Ͻ 0.01), but IMCL was unchanged. S i was increased at month 6 (P ϭ 0.05) in the CREX (37 Ϯ 18%) and LCD (70 Ϯ 34%) groups (P Ͻ 0.05) and tended to increase in the CR group (40 Ϯ 20%, P ϭ 0.08). Together the improvements in S i were related to loss in weight, fat mass, and VAT, but not IHL, IMCL, or FCS.CONCLUSIONS -Large adipocytes lead to lipid deposition in visceral and hepatic tissues, promoting insulin resistance. Calorie restriction by diet alone or with exercise reverses this trend.