A threshold for low-protein-diet–induced elevations in parathyroid hormone

Abstract

Background:We reported previously that lowering dietary protein intake in young healthy women to 0.7 g/kg depressed intestinal calcium absorption and was accompanied by elevations in parathyroid hormone (PTH). Moderate amounts of dietary protein (1.0 g/kg) did not appear to perturb calcium homeostasis. Objective: The purpose of this study was to evaluate the effect of graded intakes of dietary protein (0.7, 0.8, 0.9, and 1.0 g/kg) on calcium homeostasis. Design: The experiment consisted of 2 wk of a well-balanced diet containing moderate amounts of calcium, sodium, and protein followed by 4 d of an experimental diet containing 1 of 4 amounts of protein. Eight young healthy women received the 4 amounts of protein in random order. The average age of the subjects was 23.1 ± 2.3 y, their weight was 64 ± 3 kg, and their body mass index (in kg/m 2 ) was 24.3 ± 0.9. Results: Elevations in PTH developed by day 4 of the diets containing 0.7 and 0.8 g protein/kg but not during the diets containing 0.9 or 1.0 g protein/kg. By day 4 of the 0.7-and 0.8-g/kg diets, midmolecule PTH, calcitriol, and nephrogenous cyclic adenosine monophosphate were 1.5-3.5-fold higher than on day 0. Calcitropic hormones on day 4 of the diets containing 0.8 and 0.9 g protein/kg were within the normal range and 23-57% lower than values observed with the 0.7-and 0.8-g/kg diets (P < 0.005). Mean 24-h urinary calcium was 3.29 ± 0.35 mmol with the diet containing 0.7 g protein/kg and 3.54 ± 0.46 mmol with the diet containing 1.0 g protein/kg. Conclusions: Our data suggest that in young healthy women consuming a well-balanced diet, the current recommended dietary allowance for protein (0.8 g/kg) results in short-term perturbations in calcium homeostasis.Am J Clin Nutr 2000;72:168-73. KEY WORDSDietary protein, calcium metabolism, calcitropic hormones, vitamin D, parathyroid hormone, young healthy women, recommended dietary allowance INTRODUCTIONThe effect of dietary protein on calcium metabolism in humans was first documented nearly 80 y ago (1). There has been considerable investigative interest in the potential negative effects of a high-protein diet on mineral and skeletal homeostasis. For example, increasing dietary protein induces urinary calcium loss, negatively affects calcium balance (2), increases bone turnover (3), and may be associated with an increased risk of fracture (4). However, the effect of low-protein diets on calcium and bone homeostasis has received considerably less attention.We reported that in 16 young healthy women, 4 d of a lowprotein diet decreased urinary calcium excretion and was accompanied by elevations in calcitropic hormones; 1.5-3-fold increases were observed in concentrations of serum parathyroid hormone (PTH), 1,25(OH) 2 vitamin D (calcitriol), and urinary nephrogenous cyclic adenosine monophosphate (NcAMP; a bioindex of PTH action). The low-protein diet contained an average of 45 g protein (0.7 g/kg), including both animal and vegetable sources of protein; 20 mmol calcium; and 100 mmol sodium and was otherwi...

Bone and nutrition in elderly women: protein, energy, and calcium as main determinants of bone mineral density

“…Conversely, there is evidence that a low-protein diet might decrease Ca absorption. Kerstetter et al showed that short-term intake of a moderately low-protein (0.7 g/kg) diet decreased urinary Ca excretion and was accompanied by secondary hyperparathyroidism (as a consequence of reduced Ca absorption), while the levels of 5 0.9 g/kg with the same intake of Ca (800 mg/day) did not interfere with Ca absorption in healthy young women (Kerstetter et al, 1997(Kerstetter et al, , 2000a. Findings from the epidemiological studies imply that a low-protein diet may adversely affect bone and significantly contribute to reduced BMD (Hannan et al, 2000;Kerstetter et al, 2000b).…”

L-Amino acid sensing by the calcium-sensing receptor: a general mechanism for coupling protein and calcium metabolism?

“…Thus, the trough of the amino acid rhythm coincides with the peak of the PTH rhythm -the predicted behaviour for an acute inhibitor of PTH secretion (Figure 7). The circadian rhythm for plasma amino acids appears to be exaggerated in individuals on high protein diets but is attenuated in individuals on low protein diets (Fernstrom et al, 1979) -a circumstance in which PTH levels are mark-L-Amino acid sensing AD Conigrave et al edly elevated (Kerstetter et al, 1997(Kerstetter et al, , 2000b …”

“…Amino acid sensing mechanisms, especially for aromatic L-amino acids, also have a significant impact on digestion and absorption by the digestive tract. Finally, an amino acid sensing mechanism would appear to explain how protein and calcium metabolism are linked so that high protein intake promotes urinary calcium excretion (Allen et al, 1979;Johnson et al, 1970;Kerstetter & Allen, 1994; Figure 1) and low protein intake induces a state of secondary hyperparathyroidism (Kerstetter et al, 1997;Kerstetter et al, 2000b; Figure 2). …”

An intervention study of the effects of calcium intake on faecal fat excretion, energy metabolism and adipose tissue mRNA expression of lipid-metabolism related proteins

“…Recently, it has been shown that a high protein intake increases calcium bioavailability, making less calcium available for binding to fat in the intestine. [30][31][32][33] In the investigation by Jacobsen et al, 19 the significant effects on faecal fat excretion were only observed in the high-calcium, low-protein diets. The faecal energy content of the present investigation is comparable to the condition in the study of Jacobsen with a high protein content (that is, 23%), in which they did not observe any effects of increasing calcium intake on fat excretion.…”