Short-term low-protein make does not increase serum parathyroid hormone concentration in humans

We investigated whether inadequate dietary protein would result in increased serum parathyroid hormone (PTH) concentration, consistent with secondary hyperparathyroidism. Data from 2 controlled feeding studies were utilized. In study 1, 26 healthy women (15 young, 21-46 y, and 11 elderly, 70-81 y) consumed for 12 d each in separate trials 3 levels of protein, 1.00, 0.75, and 0.50 g protein/(kg (.) d). Blood was drawn from fasting subjects on d 12 of each trial. In study 2, 24 persons (54-80 y) were fed diets with either 1.20 g protein/(kg (.) d) for 2 wk (HPro, n = 11, 6 men, 5 women) or 1.20 g protein/(kg (.) d) for 1 wk, and then 0.50 g protein/(kg (.) d) for a 2nd week (Pro, n = 13, 6 men, 7 women). Blood was obtained from fasting subjects after wk 1 and 2. Consistent with altered protein metabolism, urinary total nitrogen excretion and blood urea nitrogen fell progressively with decreasing protein intake in study 1; in study 2, the values decreased from wk 1 to 2 in the Pro group only. Serum intact PTH concentrations did not differ among the 3 protein intakes n study 1, or between the HPro and Pro groups in study 2. These findings do not support the hypothesis that the short-term ingestion of inadequate dietary protein increases serum PTH concentration.