Supplemental essential amino acids augment the somatomedin-C/insulin-like growth factor I response to refeeding after fasting.
Level 2 - randomized trial
Individual randomized crossover trial
PubMed 3884968 · doi:10.1016/0026-0495(85)90230-6
What was done
Six normal adults underwent two fasting-refeeding cycles in a randomized crossover design. In each cycle, subjects fasted for five days and were then refed for nine days on diets providing 35 kcal/kg and 0.48 g protein/kg body weight. In one diet, 80% of nitrogen was provided as essential amino acids; in the other, 80% was provided as nonessential amino acids. A two-week control diet separated the two cycles. Plasma somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) concentrations were measured across fasting and refeeding phases.
What was found
Plasma Sm-C/IGF-I fell from a pre-fast mean of 1.64 ± 0.24 U/mL to 0.67 ± 0.18 U/mL following fasting (P < 0.001). Refeeding with the essential amino acid diet increased concentrations to 1.41 ± 0.19 U/mL (P < 0.001, a rise of 0.74 ± 0.10 U/mL). Refeeding with the nonessential amino acid diet increased concentrations from 0.74 ± 0.17 to 1.15 ± 0.15 U/mL (P < 0.01, a rise of 0.40 ± 0.11 U/mL). The increase was significantly greater with the essential amino acid diet compared to the nonessential amino acid diet (P < 0.02).
Why it matters
This demonstrates that dietary protein composition, specifically the proportion of essential amino acids, directly regulates circulating IGF-I restoration during nutritional repletion independently of total caloric and protein intake.
Limits
The study had a very small sample size (n = 6). The severe 5-day total fast in healthy adults may not generalize to clinical malnutrition, illness-induced catabolism, or routine dietary changes. The abstract does not report participant demographics, nitrogen balance metrics, or longer-term clinical outcomes.
Cited by
- supports In humans, it takes five to seven days of fasting to achieve a 50% reduction in circulating IGF-1 levels.