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Background: The skeletal muscle mass decreases with age and the responsiveness of aging muscles' protein synthesis rate (MPS) to protein intake seems to deteriorate. Objective: This study investigated the impact of 12 months of protein supplementation with or without physical exercise training on the basal and postprandial MPS and the skeletal muscle metabolome of healthy older Danes (> 65 years, 29 females/37 males). Methods: Subjects were randomized to follow one of five intervention groups: (1) carbohydrate, (2) collagen protein, (3) whey protein, (4) home-based light resistance training with whey protein, and (5) center-based heavy-load resistance training with whey protein. Before and after the intervention, a tracer infusion trial was conducted to measure basal and postprandial MPS in response to intake of a cocktail consisting of 20 g whey hydrolysate + 10 g glucose. In addition, the skeletal muscle metabolome was measured using gas chromatography–mass spectrometry (GC–MS) at basal state and 4 h after the intake of the cocktail. Results: One year of daily protein or carbohydrate supplementation did not alter the basal and protein-stimulated postprandial muscle protein synthesis rate or the muscle metabolome of healthy older Danes. Basal MPS (%/h) at baseline for all subjects were 0.0034 ± 0,011 (mean ± SD). In contrast to previous studies, no difference was observed in basal MPS between males and females (p = 0.75). With the developed untargeted GC–MS methodology, it was possible to detect and tentatively annotate > 70 metabolites from the human skeletal muscle samples. Conclusion: One year of protein supplementation in comparison to an isocaloric-control supplement seems to affect neither the MPS at basal or postprandial state nor the skeletal muscle metabolome. Clinical trial registry: Number: NCT02115698, clinicaltrials.gov/ct2/show/NCT02115698. [ABSTRACT FROM AUTHOR]

Purpose: Resistance exercise and amino acid availability are positive regulators of muscle protein net balance (NB). However, anabolic responses to resistance exercise and protein supplementation deserve further elucidation. The purpose was to compare intakes of whey, caseinate (both: 0.30 g/kg lean body mass), or a non-caloric control after heavy resistance exercise on protein turnover and mRNA expressions of forkhead homeobox type O (FOXO) isoforms, muscle RING finger 1 (MuRF1), and Atrogin1 in young healthy males. Methods: Protein turnover was determined by stable isotope-labeled leucine and femoral arteriovenous blood samples at rest and during 6-h recovery. Muscle biopsies were collected at −60 min (rest) and at 60, 210, and 360 min in the recovery period. Results: During recovery, leucine NB was significantly higher in the protein groups compared to control ( P < 0.001). Differences in leucine NB, rate of disappearance, and oxidation were observed in the early recovery period between whey and caseinate. FOXO1A and MuRF1 were upregulated at 60 and 210 min, and, in contrast, FOXO3 and Atrogin1 were downregulated at 210 and 360 min. For leucine rate of appearance and all FOXO and atrogene mRNA expressions, no differences were observed between groups. Conclusions: Whey and caseinate were equally superior to control in the 6-h recovery period and displayed temporal differences with whey having a fast and superior effect in the early part of the recovery period. Effects on mRNA expressions indicate different regulatory mechanisms on the ubiquitin ligases MuRF1 and Atrogin1 in recovery from heavy resistance exercise. [ABSTRACT FROM AUTHOR]