Higher protein intake during resistance training does not potentiate strength, but modulates gut microbiota, in middle-aged adults: a randomized control trial

Abstract

Protein intake above the Recommended Dietary Allowance (RDA) and resistance training are known anabolic stimuli to support healthy aging. Specifically, protein supplementation after resistance exercise and nightly are strategies to maximize utilization of protein intake above the RDA in healthy adults. As such, the primary objective was to examine the efficacy of protein supplementation and nutritional counseling resulting in either moderate (MOD: ~1.0 g·kg−1·d−1) or higher (HIGH: ~1.6 g·kg−1·d−1) protein intake during resistance training on strength (one-repetition maximum, 1-RM; isokinetic and isometric peak torque) in healthy middle-aged adults. Exploratory analyses include diet-exercise effects on lean body mass (LBM), clinical biomarkers, gut microbiota, and diet composition. 50 middle-aged adults (age: 50 ± 8 y, BMI: 27.2 ± 4.1 kg·m-2) were randomized to either MOD or HIGH protein intake during a 10-week resistance training program (3 × week). Participants received dietary counseling and consumed either 15 g (MOD) or 30 g (HIGH) of protein from lean beef in the immediate post-exercise period and each evening. Maximal strength (1-RM) for all upper and lower body exercises significantly increased with no effect of protein intake (P<0.050). There was a main effect of time for LBM (P<0.005). Cardiovascular, renal, or glycemic biomarkers were not affected by the intervention. Gut microbiota were associated with several health outcomes (P<0.050). In conclusion, higher protein intake above moderate amounts does not potentiate resistance training adaptations in previously untrained middle-aged adults. This trial was registered at clinicaltrials.gov as NCT03029975.

Early resistance training‐mediated stimulation of daily muscle protein synthetic responses to higher habitual protein intake in middle‐aged adults

“…All participants were informed of the experimental procedures, the study purpose and potential risks prior to giving written consent. These participants were a part of a larger study investigating the effect of dietary protein density on resistance training adaptations over 10 weeks (McKenna et al 2021). As such, we also examined relationships between the early stimulation of muscle protein synthetic sub-fractional responses to the subsequent 10 weeks' resistance training adaptations (i.e.…”

“…After eligibility was confirmed, participants completed preliminary strength tests to familiarize themselves to strength measurements. At least 72 h after exercise familiarization, participants arrived to the laboratory after an overnight fast for baseline testing (McKenna et al 2021). In brief, baseline testing consisted of assessment of body composition by dual-energy X-ray absorptiometry, resting blood pressure, oral glucose tolerance test (OGTT), and muscular strength and performance (detailed below).…”

“…In brief, baseline testing consisted of assessment of body composition by dual-energy X-ray absorptiometry, resting blood pressure, oral glucose tolerance test (OGTT), and muscular strength and performance (detailed below). After completion of baseline measures and diet records, participants were randomized and counterbalanced for age, sex, BMI and baseline strength to consume either a MOD (0.8-1.0 g kg −1 d −1 ) or HIGH (1.6-1.8 g kg −1 day −1 ) protein weight-maintenance diet (McKenna et al 2021). The research dietitian (C.F.M.)…”

“…Participants were additionally counselled by a registered dietitian to meet their protein grouping goals with protein distributed between meals within a weight-maintenance US-style diet pattern (USDA, 2015). Diet was monitored and evaluated by biweekly 3-day diet records with follow-up dietary counselling from a registered dietitian as described elsewhere (McKenna et al 2021). Briefly, dietary intake was assessed by 3-day diet records using the automated self-administered 24-h (ASA24) dietary assessment tool (version 2016, National Cancer Institute, Bethesda, MD, USA).…”

“…Immediately after every exercise session (3 days week −1 ), participants consumed an isocaloric meal consisting of minced lean beef and a carbohydrate beverage under research team supervision. Specifically, participants randomized to HIGH or MOD either consumed 6 oz minced beef steak (32 g protein) or 3 oz steak (16 g protein) with 2 g beef tallow to match dietary fat, respectively (McKenna et al 2021). Post-exercise energy intake was matched between protein conditions with a dosed dextrose (MOD: 30 g; HIGH: 12 g) beverage.…”