Weight Loss‐Induced Changes in Muscle Protein Turnover in Young Men: Effects of Dietary Protein Intake and Resistance Exercise
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abstract
A negative consequence of diet‐induced weight loss is the loss of lean body mass (LBM), particularly muscle mass, which is induced by an imbalance between rates of muscle protein synthesis (MPS) and muscle protein breakdown (MPB). Increased protein intake and resistance exercise during diet‐induced weight loss promote retention of LBM [1] by stimulating MPS. Currently, the relative contribution of MPS to hypoenergetic diet‐induced LBM loss, and the effect of protein intake and resistance exercise on these variables is not well characterized. In a single blind investigation, adult men (n=24, BMI=28.6±0.6kg/m2, age=22±1y) underwent 10 days of a controlled diet with a 40% reduction in energy intake to create an energy deficit, while performing unilateral resistance exercise and consuming either lower protein (LP) (1.2g/kg/d protein, n=12) or higher protein (HP) (2.4g/kg/d protein, n=12). Pre‐ and post‐intervention testing included DXA, primed constant infusion of ring‐[13C6]‐phenylalanine to measure acute MPS in the fasted state and skeletal muscle biopsies to measure gene and protein expression. Total weight loss (−1.7±0.1kg) and fat mass loss (−0.7±0.1kg) did not differ between groups; however, appendicular lean mass of the exercised leg was preserved compared to the rested leg in both groups (exercise= −0.1±0.1kg, rest= −0.4±0.1kg, p<0.05). Mixed MPS was significantly reduced in both groups following weight loss (HP= −14±4% and LP= −27±2%, p<0.05). In the exercised leg, mixed MPS was preserved in the lower protein group and elevated above baseline in the higher protein group (14±6% p<0.05) 48 hrs following the last exercise bout. Gene expression of TRAF6 was increased in the rested leg of the lower protein group (p<0.05), but there was no change in TRAF6 protein expression at any time point in either group. Gene expression of other targets in the ubiquitin‐proteasome and autophagic‐lysosomal pathways (Atrogin‐1, MuRF‐1, Foxo3a, LC3, Gabarapl1, Ulk2, Beclin1) did not change with weight loss in either group. Protein expression of p‐Foxo3a (Ser253) and p‐TSC2 (Thr1462) also did not change with weight loss in either group. These results suggest that reductions in MPS are the likely reason for LBM loss during the early phase of diet‐induced weight loss. Resistance exercise can help to preserve (LP) or even elevate (HP) rates of fasted MPS, which, in concordance with our earlier work [1], promotes LBM retention.Support or Funding InformationSupported by NSERC and OGS
