The effect of selective amino acid supplementation on calcium absorption during a low protein diet

Abstract

Increasing dietary protein intake within a physiologic range stimulates intestinal Ca absorption but it is not known if specific amino acids (AA) or dietary protein as a whole is responsible for this effect. We therefore selectively supplemented a low protein (0.7 g/kg) diet with either aromatic (Trp, Phe, His) or dibasic (Arg, Lys) AA to achieve intakes comparable to the content of a high protein diet (2.1 g/kg) and measured Ca absorption. Fourteen young women were randomized to a placebo‐controlled, doubleblind, cross‐over feeding trial in which each subject ingested, in random order, a 6‐day low protein diet supplemented with aromatic AA, dibasic AA, or methylcellulose capsules (control) after a 10‐day adjustment period. All subjects ingested all 3 diets. Intestinal Ca absorption was measured between days 5 and 6 using dual stable Ca isotopes. There was no difference in Ca absorption between the diet supplemented with aromatic AA and the control diet (22.9±2.0% vs.22.3±1.4% respectively, p = 0.322). However, Ca absorption was significantly higher with dibasic AA supplementation (25.2±1.4% vs. 22.3±1.4%, p = 0.047). Individuals with protein intakes below the RDA may benefit from Arg and Lys supplementation to improve Ca economy.