Effects of protein intake or exercise on 24 h urinary solute excretion

The effects of protein intake or exercise on 24 h urinary solute excretion, were evaluated in 10 female 18-19 yr of age. This study was performed during four periods: a low-protein diet (30 g x 5 days), a normal-protein diet (control, 60 g x 5 days), a high-protein diet (90 g x 5 days), and exercise loading with a normal-protein diet. (The amount of plant protein was kept constant to be 24 g/day) The following results were obtained: 1. In the case of exercise loading, urinary potassium (K) and nitrogen (N) excretions decreased significantly, while urinary sodium (Na), chlorine (Cl), calcium (Ca), and phosphate (P) excretions showed no significant differences compared with control values. 2. With the low-protein diet, urinary Ca excretion decreased significantly compared with those in normal or high-protein diet. 3. The apparent fractional absorption of Na, Cl, and Ca in the female on the high-protein diet was significantly higher than that in those on the low-protein diet. These results suggest the following: 1. The amount of urinary K excretion is not only directly influenced by K intake, but also by K metabolism, such as K+ transport between extra- and intracellular spaces. 2. Although urinary Ca excretion was not increased by the increment in protein in the diet from 60 g/day to 90 g/day, it is necessary to evaluate both quantity and quality of a protein diet. 3. Protein intake of more than 60 g/day is necessary for an effective increase in Ca and NaCl absorption.