The bioactive peptide cyclo(His-Pro) may be absorbed following ingestion of nutritional supplements that contain it

Food contains a number of peptides with potential bioactivity. We previously found ng/mliter to mcg/mliter quantities of cyclo(His-Pro)-like immunoreactivity in a number of foods and nutritional supplements. A number of activities have been attributed to cyclo(His-Pro) (CHP), including appetite inhibition and inhibition of insulin secretion in vitro. We wondered whether the cyclo(His-Pro)-like immunoreactivity present in nutritional supplements might be absorbed and, if so, whether parameters of insulin secretion would be altered.

After performing a pilot study which suggested some common nutritional supplements contain CHP, a follow-up study was done to confirm and expand the findings of the pilot study. Eight fasting volunteers ingested approximately 250 mL of a CHP-containing supplement one day, and then an equienergetic CHP-free supplement the next.

Blood drawn for CHP, insulin, glucose, and C-peptide a number of times on both days revealed that when volunteers ingested CHP-containing supplements, CHP levels at 120 minutes were significantly higher than baseline (7.69 +/- 0.50 pmol/mL vs. 9.18 +/- 0.48 pmol/mL; p = 0.011 in the CHP group and 7.90 +/- 0.85 pmol/mL vs. 7.22 +/- 0.73 pmol/mL, p > 0.3 in the CHP-free group) and significantly higher than levels achieved when they drank CHP-free supplements. Levels of glucose, insulin, and C-peptide were not different in the two groups.

CHP in nutritional supplements may be absorbed when ingested orally and does not grossly affect glucose or parameters of insulin secretion.