Urine C-peptide and creatinine (Jaffe Method) excretion in healthy young adults on varied diets: sustained effects of varied carbohydrate, protein, and meat content

Abstract

We studied effects of isocaloric diets of varied composition (each diet offered for 5 to 7 days) on urine C-peptide and creatinine excretion in eight healthy subjects. C-peptide excretion was higher on the high carbohydrate (60% CHO, 20% PRO) and high protein (45% CHO, 30% PRO) diets than on the low carbohydrate (30% CHO, 20% PRO) and low protein diets (45% CHO, 10% PRO). C-peptide excretion correlated with total kilocalories ingested (r = 0.594, p < 0.001), and also with CHO (r = 0.469, p = 0.003) and PRO intake (r = 0.453, p = 0.004). Multiple regression analysis is given by the formula: Urine C-peptide (nmol/24 h) = −17.3 + 0.01 (kcal/24 h) + 0.021 (gm CHO/24 h) + 0.049 (gm PRO/24 h)Creatinine excretion was related to body weight (r = 0.959, p < 0.001) and also to total PRO intake (r = 0.569, p < 0.001) and meat intake (r = 0.367, p < 0.05).We conclude that diet composition, especially protein intake, is an important stimulus to sustained insulin production as measured by C-peptide in healthy subjects. Diet composition has a significant impact on creatinine excretion. Urine creatinine cannot be assumed to reflect only lean body weight when it is used as a measure of the adequacy of timed urine collections.