Pronounced energy restriction with elevated protein intake results in no change in proteolysis and reductions in skeletal muscle protein synthesis that are mitigated by resistance exercise.
Level 2 - randomized trial
Individual randomized controlled trial with within-subject unilateral exercise control
PubMed 28899879 · doi:10.1096/fj.201700158RR
What was done
Twenty-four young adult men (BMI 28.6 ± 0.6 kg/m², age 22 ± 1 yr) underwent 10 days of a 40% dietary energy deficit while performing unilateral resistance exercise. Participants were randomized to either a lower-protein (1.2 g/kg/d, n = 12) or higher-protein (2.4 g/kg/d, n = 12) intake. Acute postabsorptive muscle protein synthesis (MPS) and muscle protein breakdown (MPB) were measured using primed constant infusions of ring-[13C6]phenylalanine and 15[N]phenylalanine, integrated MPS was tracked with D2O, and body composition was assessed via DXA.
What was found
Acute postabsorptive MPS decreased after energy restriction in the rested legs of both the higher-protein group (from 0.059 ± 0.006 to 0.051 ± 0.009%/h) and the lower-protein group (from 0.061 ± 0.005 to 0.045 ± 0.006%/h; P < 0.05). Resistance exercise attenuated this decline in both the higher-protein (0.067 ± 0.01%/h) and lower-protein (0.061 ± 0.006%/h) legs, with integrated MPS showing a similar pattern. In contrast, MPB remained unchanged across conditions (energy balance: 0.080 ± 0.01%/hr; energy-restricted rested: 0.078 ± 0.008%/hr; energy-restricted exercised: 0.079 ± 0.006%/hr).
Why it matters
The findings demonstrate that lean mass loss during acute severe caloric restriction is primarily driven by reduced muscle protein synthesis rather than accelerated proteolysis, and resistance exercise effectively offsets this suppression.
Limits
The intervention was short (10 days) and tested exclusively young adult men with overweight BMI, limiting generalizability to females, older adults, or prolonged weight loss. Functional performance and long-term changes in body composition were not measured.
Cited by
- supports Caloric deficits act as a catabolic stimulus on skeletal muscle.