Leucine Supplementation Does Not Alter Insulin Sensitivity in Prefrail and Frail Older Women following a Resistance Training Protocol.
Study Goal
The researchers aimed to determine whether leucine supplementation (compared to alanine placebo) combined with resistance training improves insulin sensitivity in prefrail and frail older women.
Results Summary
The study found no significant effects of leucine supplementation (vs. alanine) on insulin sensitivity or postprandial glucose/insulin responses. Both groups showed increased lean body mass and reduced body fat, likely due to resistance training.
Population
Nondiabetic prefrail and frail older women (mean age 77.5 years, BMI 25.1).
Effective Dosage
7.5 g/day of L-alanine (placebo).
Duration
3 months.
Interactions
None mentioned.
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
resistance training | increase | insulin sensitivity | frail older women | - | improved | #1 |
leucine supplementation and resistance training | no change | insulin sensitivity | nondiabetic prefrail and frail older women | - | was not affected | #2 |
leucine supplementation and resistance training | no change | postprandial areas under the curve of serum insulin | nondiabetic prefrail and frail older women | - | No significant time, group, or interaction effects were observed | #3 |
leucine supplementation and resistance training | no change | postprandial areas under the curve of plasma glucose | nondiabetic prefrail and frail older women | - | No significant time, group, or interaction effects were observed | #4 |
leucine supplementation and resistance training | no change | resting energy expenditure | nondiabetic prefrail and frail older women | - | No significant time, group, or interaction effects were observed | #5 |
leucine supplementation and resistance training | increase | total lean body mass | nondiabetic prefrail and frail older women | 0.76 ± 0.13 kg | increased significantly | #6 |
leucine supplementation and resistance training | decrease | percentage body fat | nondiabetic prefrail and frail older women | -0.92 ± 0.33 kg | decreased significantly | #7 |
BACKGROUND: Frailty is a clinical condition associated with loss of muscle mass and strength (sarcopenia). Although sarcopenia has multifactorial causes, it might be partly attributed to a blunted response to anabolic stimuli. Leucine acutely increases muscle protein synthesis, and resistance training (RT) is the strongest stimuli to counteract sarcopenia and was recently shown to improve insulin sensitivity (IS) in frail older women. Discrepancies exist regarding whether chronic supplementation of leucine in conjunction with RT can improve muscle mass and IS. OBJECTIVE: The aim of this double-blinded placebo-controlled study was to determine the effects of leucine supplementation and RT on IS in prefrail and frail older women. METHODS: Using the Fried criteria, 19 nondiabetic prefrail (1-2 criteria) and frail (≥3 criteria) older women (77.5 ± 1.3 y; body mass index (kg/m2): 25.1 ± 0.9) underwent a 3-mo intervention of RT 3 times/wk with protein-optimized diet of 1.2 g·kg-1·d-1 and 7.5 g·d-1 of l-leucine supplementation compared with placebo l-alanine. Pre-/postintervention primary outcomes were fasting plasma glucose, serum insulin, and 4-h responses to a standard meal of complete liquid formula. Secondary outcomes of resting energy expenditure using indirect calorimetry and body composition using dual-energy X-ray absorptiometry were obtained. Paired t tests analyzed pooled data, and 2-factor repeated-measures ANOVA determined supplementation, training, and interaction effects. RESULTS: No significant time, group, or interaction effects were observed for postprandial areas under the curve of serum insulin or plasma glucose or for resting energy expenditure in l-leucine compared with l-alanine. Total lean body mass increased and percentage body fat decreased significantly for both groups postintervention (0.76 ± 0.13 and -0.92 ± 0.33 kg, respectively; time effect: P < 0.01). CONCLUSIONS: IS was not affected by RT and leucine supplementation in nondiabetic prefrail and frail older women. Therefore, leucine supplementation does not appear to influence IS under these conditions. This trial was registered at clinicaltrials.gov as NCT01922167.