Acute ingestion of a ketone monoester, whey protein, or their co-ingestion in the overnight postabsorptive state elicit a similar stimulation of myofibrillar protein synthesis rates in young males: a double-blind randomized trial.

BACKGROUND: Ketone bodies may have anabolic effects in skeletal muscle via their capacity to stimulate protein synthesis. Whether orally ingested exogenous ketones can stimulate postprandial myofibrillar protein synthesis (MyoPS) rates with and without dietary protein co-ingestion is unknown. OBJECTIVES: This study aimed to evaluate the effects of ketone monoester intake and elevated blood ß-hydroxybutyrate (ß-OHB) concentration, with and without dietary protein co-ingestion, on postprandial MyoPS rates and mechanistic target of rapamycin complex 1 (mTORC1) pathway signaling. METHODS: In a randomized, double-blind, parallel group design, 36 recreationally active healthy young males (age: 24.2 ± 4.1 y; body fat: 20.9% ± 5.8%; body mass index: 23.4 ± 2 kg/m2) received a primed continuous infusion of L-[ring-2H5]-phenylalanine and ingested one of the following: 1) the ketone monoester (R)-3-hydroxybutyl (R)-3-hydroxybutyrate (KET), 2) 10 g whey protein (PRO), or 3) the combination of both (KET+PRO). Blood and muscle biopsy samples were collected during basal and postprandial (300 min) conditions to assess ß-OHB, glucose, insulin, and amino acid concentrations, MyoPS rates, and mTORC1 pathway signaling. RESULTS: Capillary blood ß-OHB concentration increased similarly during postprandial conditions in KET and KET+PRO, with both being greater than PRO from 30 to 180 min (treatment × time interaction: P < 0.001). Postprandial plasma leucine and essential amino acid (EAA) incremental area under the curve (iAUC) over 300 min was greater (treatment: both P < 0.001) in KET+PRO compared with PRO and KET. KET, PRO, and KET+PRO stimulated postprandial MyoPS rates (0-300 min) higher than basal conditions [absolute change: 0.020%/h; (95% CI: 0.013, 0.027%/h), 0.014%/h (95% CI: 0.009, 0.019%/h), 0.019%/h (95% CI: 0.014, 0.024%/h), respectively (time: P < 0.001)], with no difference between treatments (treatment: P = 0.383) or treatment × time interaction (interaction: P = 0.245). mTORC1 pathway signaling responses did not differ between treatments (all P > 0.05). CONCLUSIONS: Acute oral intake of a ketone monoester, 10 g whey protein, or their co-ingestion in the overnight postabsorptive state elicit a similar stimulation of postprandial MyoPS rates in healthy young males. This trial was registered at clinicaltrials.gov as NCT04565444 (https://clinicaltrials.gov/study/NCT04565444).

Evaluation of sex-based differences in resistance exercise training-induced changes in muscle mass, strength, and physical performance in healthy older (≥60 y) adults: A systematic review and meta-analysis.

The objective of this systematic review and meta-analysis was to determine if there are sex-based differences in adaptations to resistance exercise training in healthy older adults. Following the screening process, data from 36 studies comparing older males and females (602 males; 703 females; ≥60 years of age) for changes in skeletal muscle size, muscle strength, and/or physical performance following the same resistance exercise training intervention were extracted. Mean study quality was 16/29 (modified Downs and Black checklist), considered moderate quality. Changes in absolute upper-body (Effect Size [ES] = 0.81 [95% CI 0.54, 1.09], P < 0.001), and lower-body (ES = 0.40 [95% CI 0.24, 0.56], P < 0.001) strength were greater in older males than females. Alternatively, changes in relative upper-body (ES = -0.46 [95% CI -0.77, -0.14], P < 0.01), and lower-body (ES = -0.24 [95% CI -0.42, -0.06], P < 0.01) strength were greater in older females than males. Changes in absolute, but not relative, whole-body fat-free mass (ES = 0.18 [95% CI 0.04, 0.33], P < 0.05) were greater in older males than females. There were no sex-based differences for absolute or relative changes in limb muscle size, muscle fiber size, or physical performance.