Dietary components that regulate serum somatomedin-C concentrations in humans.
Level 3 - non-randomized controlled study
Small prospective repeated-measures interventional study in healthy humans without explicit randomization reported
PubMed 6681614 · doi:10.1172/jci110757
What was done
Five normal-weight adult volunteers underwent 5-day fasts on three separate occasions, followed by 5 days of refeeding with three distinct diets: a normal control diet, an isocaloric protein-deficient diet (containing 32% of control protein), and a diet deficient in both protein and total energy. Serum somatomedin-C (IGF-1) and daily nitrogen balance were measured.
What was found
Serum somatomedin-C fell from a baseline mean of 1.85 +/- 0.39 U/ml to 0.67 +/- 0.16 U/ml after 5 days of fasting (P < 0.005). Refeeding with a normal diet raised levels to 1.26 +/- 0.20 U/ml. Refeeding with an isocaloric protein-deficient diet resulted in a significantly smaller recovery to 0.90 +/- 0.24 U/ml (P < 0.05). Refeeding with both protein and energy restriction caused levels to decrease further to 0.31 +/- 0.06 U/ml. Across fasting and refeeding states, somatomedin-C fluctuations correlated strongly with daily nitrogen balance (r = 0.90).
Why it matters
This study demonstrates that circulating somatomedin-C is highly sensitive to acute nutritional status in humans, requiring adequate intake of both calories and protein for maintenance and recovery, making it a potential biomarker for nutritional response.
Limits
The study included only five participants, did not state whether the refeeding sequence was randomized, examined only short-term 5-day periods, and did not evaluate isolated energy restriction without protein restriction.
Cited by
- supports In humans, it takes five to seven days of fasting to achieve a 50% reduction in circulating IGF-1 levels.