Changes in Body Composition, Muscle Strength, and Fat Distribution Following Kidney Transplantation.

Rationale & Objective: Low muscle mass relative to fat mass (relative sarcopenia) has been associated with mortality and disability but has not been examined after kidney transplantation. We studied how measures of body composition change after receipt of a kidney allograft.

Study Design: Prospective longitudinal cohort study.

Setting & Participants: 60 kidney transplant recipients, aged 20-60 years, at the University of Pennsylvania.

Exposure: Kidney transplantation.

Outcome: Dual-energy x-ray absorptiometry measures of fat mass index (FMI) and appendicular lean mass index (ALMI, representing muscle mass), computed tomography measures of muscle density (low density represents increased intramuscular adipose tissue), dynamometer measures of leg muscle strength, and physical activity. ALMI relative to FMI (ALM) is an established index of relative sarcopenia.

Analytical Approach: Measures expressed as age, sex, and race-specific z scores for transplant recipients were compared with 327 healthy controls. Regression models were used to identify correlates of change in outcome z scores and compare transplant recipients with controls.

Results: At transplantation, ALMI, ALMI, muscle strength, and muscle density z scores were lower versus controls (all P≤0.001). Transplant recipients received glucocorticoids throughout. The prevalence of obesity increased from 18% to 45%. Although ALMI increased after transplantation (P<0.001) and was comparable with the controls from 6 months onward, gains were outpaced by increases in FMI, resulting in persistent ALMI deficits (mean z score of-0.31 at 24 months; P=0.02 vs controls). Muscle density improved after transplantation despite gains in FMI (P=0.02). Muscle strength relative to ALMI also improved (P=0.04) but remained low compared with controls (P=0.01). Exercise increased in the early months after transplantation (P<0.05) but remained lower than controls (P = 0.02).

Limitations: Lack of muscle biopsies precluded assessment of muscle histology and metabolism.

Conclusions: The 2-year interval after kidney transplantation was characterized by gains in muscle mass and strength that were outpaced by gains in fat mass, resulting in persistent relative sarcopenia.