Nutritional status affects renal 3-methylhistidine handling in humans

The plasma concentration of 3-methylhistidine (3MH) has been used in the assessment of nutritional status. Because urinary excretion is the sole route of elimination, and hence a potential determinant of the plasma concentration, 3MH renal handling was examined under different nutritional conditions. Ten obese women consumed a meat-free maintenance energy diet for 4 days before undergoing a 21-day total fast, after which they were assigned into two groups (n = 5) that received 7 days of hypocaloric feeding with 80 g of either milk protein or carbohydrate. 3MH excretion and plasma levels decreased in parallel during fasting and protein refeeding, suggesting that the plasma concentration accurately reflected a decrease of myofibrillar protein turnover, but carbohydrate refeeding was associated with a 31% increase in plasma 3MH (P less than .05) despite a concurrent 28% decrease in its excretion (P less than .05). This was due to a 41% decrease in 3MH renal clearance (P less than .05). Creatinine and urea clearances changed insignificantly in all diet periods. Plasma histidine (HIS) concentrations decreased with fasting and carbohydrate refeeding (P less than .05). 3MH clearance was found to be related to the plasma HIS/3MH concentration ratio (r = .60, P less than .001). Under some circumstances, an altered plasma HIS concentration appears to influence renal 3MH clearance and hence its plasma concentration.