EFFECTS OF HIGH PROTEIN INTAKE ON BONE TURNOVER IN LONG-TERM BED REST IN WOMEN

Purpose: Bed rest (BR) causes bone loss, even in otherwise healthy subjects. Several studies suggest that ambulatory subjects may benefit from high protein intake to stimulate protein synthesis and to maintain muscle mass. However, increasing protein intake above the recommended daily intake without adequate calcium- and potassium intake may increase bone resorption. We hypothesized that a regimen of high protein intake (HiPROT), applied in an isocaloric manner during BR with calcium and potassium intake meeting recommended values, would prevent any effect of BR on bone turnover. Methods: After a 20-day ambulatory adaptation to a controlled environment, 16 women participated in a 60-day, 6° head-down-tilt (HDT) BR and were assigned randomly to one of two groups. Control (CON) subjects (n=8) received 1 g/kg body mass/d dietary protein. HiPROT subjects (n=8) received 1.45 g protein/kg body mass/d plus an additional 0.72 g branched-chain amino acids (BCAA) per day during BR. All subjects received an individually tailored diet (before HDTBR: 1888±98 kcal/d; during HDTBR: 1604±125 kcal/d; after HDTBR: 1900±262 kcal/d), with the CON group’s diet being higher in fat and carbohydrate intake. Results: High protein intake exacerbated the BR-induced increase in bone resorption marker C-telopeptide (>30%) (pThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author