Prolonged Adaptation to a Low or High Protein Diet Does Not Modulate Basal Muscle Protein Synthesis Rates - A Substudy.
Study Goal
The researchers aimed to assess the impact of prolonged adaptation to low versus high dietary protein intake on whole-body protein turnover and basal muscle protein synthesis rates.
Results Summary
After 12 weeks, the high-protein diet resulted in a more negative whole-body protein balance and higher protein breakdown, synthesis, and phenylalanine hydroxylation rates compared to the low-protein diet, but basal muscle protein synthesis rates remained similar between groups.
Population
40 subjects (subgroup of 7 men and 8 women, BMI 22.8±2.3 kg/m², age 24.3±4.9 y).
Effective Dosage
High protein (2.4 g/kg/d) vs. low protein (0.4 g/kg/d).
Duration
12 weeks.
Interactions
None mentioned.
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
high protein diet (2.4 g protein/kg/d) | decrease | whole-body protein balance in the fasted state | subjects selected from the study | -4.1±0.5 vs -2.7±0.6 μmol phenylalanine/kg/h | was more negative | #1 |
high protein diet (2.4 g protein/kg/d) | increase | whole-body protein breakdown rates | subjects selected from the study | 43.0±4.4 vs 37.8±3.8 μmol phenylalanine/kg/h | were significantly higher | #2 |
high protein diet (2.4 g protein/kg/d) | increase | whole-body protein synthesis rates | subjects selected from the study | 38.9±4.2 vs 35.1±3.6 μmol phenylalanine/kg/h | were significantly higher | #3 |
high protein diet (2.4 g protein/kg/d) | increase | phenylalanine hydroxylation rates | subjects selected from the study | 4.1±0.6 vs 2.7±0.6 μmol phenylalanine/kg/h | were significantly higher | #4 |
low protein diet (0.4 g protein/kg/d) | no change | basal muscle protein synthesis rates | subjects selected from the study | 0.042±0.01 vs 0.045±0.01%/h | were maintained | #5 |
low-protein intake (0.4 g/kg/d) | no change | whole-body protein balance | subjects in the overnight fasted state | - | does not result in a more negative | #6 |
low-protein intake (0.4 g/kg/d) | no change | basal muscle protein synthesis rates | subjects in the overnight fasted state | - | does not lower | #7 |
BACKGROUND: Based on controlled 36 h experiments a higher dietary protein intake causes a positive protein balance and a negative fat balance. A positive net protein balance may support fat free mass accrual. However, few data are available on the impact of more prolonged changes in habitual protein intake on whole-body protein metabolism and basal muscle protein synthesis rates. OBJECTIVE: To assess changes in whole-body protein turnover and basal muscle protein synthesis rates following 12 weeks of adaptation to a low versus high dietary protein intake. METHODS: A randomized parallel study was performed in 40 subjects who followed either a high protein (2.4 g protein/kg/d) or low protein (0.4 g protein/kg/d) energy-balanced diet (30/35/35% or 5/60/35% energy from protein/carbohydrate/fat) for a period of 12 weeks. A subgroup of 7 men and 8 women (body mass index: 22.8±2.3 kg/m2, age: 24.3±4.9 y) were selected to evaluate the impact of prolonged adaptation to either a high or low protein intake on whole body protein metabolism and basal muscle protein synthesis rates. After the diet, subjects received continuous infusions with L-[ring-2H5]phenylalanine and L-[ring-2H2]tyrosine in an overnight fasted state, with blood samples and muscle biopsies being collected to assess post-absorptive whole-body protein turnover and muscle protein synthesis rates in vivo in humans. RESULTS: After 12 weeks of intervention, whole-body protein balance in the fasted state was more negative in the high protein treatment when compared with the low protein treatment (-4.1±0.5 vs -2.7±0.6 μmol phenylalanine/kg/h;P<0.001). Whole-body protein breakdown (43.0±4.4 vs 37.8±3.8 μmol phenylalanine/kg/h;P<0.03), synthesis (38.9±4.2 vs 35.1±3.6 μmol phenylalanine/kg/h;P<0.01) and phenylalanine hydroxylation rates (4.1±0.6 vs 2.7±0.6 μmol phenylalanine/kg/h;P<0.001) were significantly higher in the high vs low protein group. Basal muscle protein synthesis rates were maintained on a low vs high protein diet (0.042±0.01 vs 0.045±0.01%/h;P = 0.620). CONCLUSIONS: In the overnight fasted state, adaptation to a low-protein intake (0.4 g/kg/d) does not result in a more negative whole-body protein balance and does not lower basal muscle protein synthesis rates when compared to a high-protein intake. TRIAL REGISTRATION: Clinicaltrials.gov NCT01551238.