Diet and indices of bone breakdown and acid production in bed rest subjects
Diet and acid-base balance can affect bone loss during simulated weightlessness. The present study evaluates the effects of acid and base components of diet on bone resorption markers before, during, and after 60-90 days of bed rest at -6° head-down tilt position. A total of eleven subjects (8M, 3F; age 26-44 y) participated in the present study. Urine samples from the subjects were analyzed for a relationship between dietary patterns and markers of bone metabolism. This study examines two procedures for estimating acid production in the body by comparing urinary net acid excretion (NAEindirect ) and by measuring the animal protein to potassium ratio, as estimated from dietary intake. It is hypothesized that both estimations would have significant correlations between markers of bone breakdown NTX (N-telopeptide) and PYD (pyridinoline). Results confirmed that bone resorption increased during bed rest as indicated by the collagen crosslinks NTX and PYD. In addition, significant correlations were recorded between NAEindirect and NTX (p<0.01), and PYD (p<0.01) during bed rest. However, the ratio of animal protein to potassium intake was not significantly correlated with NTX or PYD, suggesting further research on this method of approximating acid load is necessary.