Background Protein supplementation alone or combined with resistance training has been proposed to be effective in counteracting age-related losses of muscle mass and strength. Objectives To investigate the effect of protein supplementation alone or combined with light-intensity or heavy-load resistance exercise on muscle size, strength, and function in older adults. Methods In a 1-y randomized controlled trial, 208 healthy older adults (>65 y) were randomly assigned to 1 of 5 interventions: 1) carbohydrate supplementation (CARB); 2) collagen protein supplementation (COLL); 3) whey protein supplementation (WHEY); 4) light-intensity resistance training 3–5 times/wk with whey protein supplementation (LITW); and 5) heavy resistance training 3 times weekly with whey protein supplementation (HRTW). Protein supplements contained 20 g protein + 10 g carbohydrate, whereas CARB contained 30 g of carbohydrates. All intervention groups received the supplement twice daily. The primary outcome was change in the quadriceps cross-sectional area (qCSA). Secondary outcomes included measures of lower extremity strength and power, functional capabilities, and body composition. Results There were 184 participants who completed the study. COLL and WHEY did not affect any measured parameter compared to CARB. Compared to WHEY, HRTW improved the qCSA size (between-group difference, +1.68 cm2; 95% CI, +0.41 to +2.95 cm2; P = 0.03), as well as dynamic (+18.4 Nm; 95% CI, +10.1 to +26.6 Nm; P < 10−4) and isometric knee extensor strength (+23.9 Nm; 95% CI, +14.2 to +33.6 Nm; P < 10−5). LITW did not improve the qCSA size, but increased dynamic knee extensor strength compared to WHEY (+13.7 Nm; 95% CI, +5.3 and +22.1 Nm; P = 0.01). Conclusions Recommending protein supplementation as a stand-alone intervention for healthy older individuals seems ineffective in improving muscle mass and strength. Only HRTW was effective in both preserving muscle mass and increasing strength. Thus, we recommend that future studies investigate strategies to increase long-term compliance to heavy resistance exercise in healthy older adults. This trial was registered at clinicaltrials.gov as NCT02034760.

When humans age, changes in body composition arise along with lifestyle‐associated disorders influencing fitness and physical decline. Here we provide a comprehensive view of dietary intake, physical activity, gut microbiota (GM), and host metabolome in relation to physical fitness of 207 community‐dwelling subjects aged +65 years. Stratification on anthropometric/body composition/physical performance measurements (ABPm) variables identified two phenotypes (high/low‐fitness) clearly linked to dietary intake, physical activity, GM, and host metabolome patterns. Strikingly, despite a higher energy intake high‐fitness subjects were characterized by leaner bodies and lower fasting proinsulin‐C‐peptide/blood glucose levels in a mechanism likely driven by higher dietary fiber intake, physical activity and increased abundance of Bifidobacteriales and Clostridiales species in GM and associated metabolites (i.e., enterolactone). These factors explained 50.1% of the individual variation in physical fitness. We propose that targeting dietary strategies for modulation of GM and host metabolome interactions may allow establishing therapeutic approaches to delay and possibly revert comorbidities of aging.

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Purpose Numerous daily tasks such as walking and rising from a chair involve bilateral lower limb movements. During such tasks, lower extremity function (LEF) may be compromised among older adults. LEF may be further impaired due to high degrees of between‐limb asymmetry. The present study investigated the prevalence of between‐limb asymmetry in muscle mass, strength, and power in a cohort of healthy older adults and examined the influence of between‐limb asymmetry on LEF. Methods Two hundred and eight healthy older adults (mean age 70.2 ± 3.9 years) were tested for LEF (400 m walking and 30‐seconds chair stand). Furthermore, maximal isometric and dynamic knee extensor strength, leg extensor power, and lower limb lean tissue mass (LTM) were obtained unilaterally. Results Mean between‐limb asymmetry in maximal muscle strength and power ranged between 10% and 13%, whereas LTM asymmetry was 3 ± 2.3%. Asymmetry in dynamic knee extensor strength was larger for women compared with men (15.0 ± 11.8% vs 11.1 ± 9.5%; P = .005) Leg strength and power were positively correlated with LEF (r2 = .43‐.46, P < .001). The weakest leg was not a stronger predictor of LEF than the strongest leg. Between‐limb asymmetry in LTM and isometric strength was negatively associated with LEF (LTM; r2 = .12, P = .005, isometric peak torque; r2 = 0.40, P = .03.) but dynamic strength and power were not. Conclusion The present study supports the notion that in order to improve or maintain LEF, healthy older adults should participate in training interventions that increase muscle strength and power, whereas the effects of reducing between‐limb asymmetry in these parameters might be of less importance.