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Effects of 12 Months of Caloric Restriction on Muscle Mitochondrial Function in Healthy Individuals

Context
The effects of caloric restriction (CR) on in vivo muscle mitochondrial function in humans are controversial.


Objective
We evaluated muscle mitochondrial function and associated transcriptional profiles in nonobese humans after 12 months of CR.


Design
Individuals from an ancillary study of the CALERIE 2 randomized controlled trial were assessed at baseline and 12 months after a 25% CR or ad libitum (control) diet.


Setting
The study was performed at Pennington Biomedical Research Center in Baton Rouge, LA.


Participants
Study participants included 51 (34 female subjects, 25 to 50 years of age) healthy nonobese individuals randomized to 1 of 2 groups (CR or control).


Intervention
This study included 12 months of a 25% CR or ad libitum (control) diet.


Main Outcomes
In vivo mitochondrial function [maximal ATP synthesis rate (ATPmax), ATPflux/O2 (P/O)] was determined by 31P-magnetic resonance spectroscopy and optical spectroscopy, and body composition was determined by dual-energy X-ray absorptiometry. In a subset of individuals, a muscle biopsy was performed for transcriptional profiling via quantitative reverse transcription polymerase chain reaction and microarrays.


Results
Weight, body mass index (BMI), fat, and fat-free mass (P < 0.001 for all) significantly decreased at month 12 after CR vs control. In vivo ATPmax and P/O were unaffected by 12 months of CR. Targeted transcriptional profiling showed no effects on pathways involved in mitochondrial biogenesis, function, or oxidative stress. A subgroup analysis according to baseline P/O demonstrated that a higher (vs lower) P/O was associated with notable improvements in ATPmax and P/O after CR.


Conclusions
In healthy nonobese humans, CR has no effect on muscle mitochondrial function; however, having a "more coupled" (versus "less coupled") phenotype enables CR-induced improvements in muscle mitochondrial function.