Supplementing a low-protein diet with dibasic amino acids increases urinary calcium excretion in young women

Abstract

Increasing dietary protein within a physiologic range stimulates intestinal calcium absorption, but it is not known if specific amino acids or dietary protein as a whole are responsible for this effect. Therefore, we selectively supplemented a low-protein (0.7 g/kg) diet with either the calcium-sensing receptor-activating amino acids (CaSR-AAAs) L-tryptophan, L-phenylalanine, and L-histidine, or the dibasic amino acids (DAAs) L-arginine and L-lysine, to achieve intakes comparable to the content of a high-protein diet (2.1 g/kg) and measured intestinal calcium absorption. Fourteen young women took part in a placebo-controlled, double-blind, crossover feeding trial in which each participant ingested a 6-d low-protein diet supplemented with CaSR-AAAs, DAAs, or methylcellulose capsules (control) after an 11-d adjustment period. All participants ingested all 3 diets in random order. Intestinal calcium absorption was measured between days 5 and 6 using dual-stable calcium isotopes ((42)Ca, (43)Ca, and (44)Ca). There was no difference in calcium absorption between the diet supplemented with CaSR-AAAs (22.9 ± 2.0%) and the control diet (22.3 ± 1.4%) (P = 0.64). However, calcium absorption tended to be greater during the DAA supplementation period (25.2 ± 1.4%) compared with the control diet period (22.3 ± 1.4%) (P < 0.10). Larger and longer clinical trials are needed to clarify the possible benefit of arginine and lysine on calcium absorption.

FIGURE 1

Flow diagram displaying recruitment, enrollment, and random assignment of study participants. Fourteen healthy young women took part in a crossover-design feeding study in which they received 3 experimental diets in random order (control, CaSR-AAA–supplemented, and DAA-supplemented; n = 14 for each experimental diet). CaSR-AAA, calcium-sensing receptor-activating amino acid; DAA, dibasic amino acid.

FIGURE 2

Urinary calcium excretion (A) and intestinal calcium absorption (B) by 14 healthy young women on day 5 of the control and DAA-supplemented low-protein diet periods. *Different from control, P < 0.05; **different from control, 0.05 < P < 0.10; ***effect size = 0.54 ± 0.1. DAA, dibasic amino acid.