Effects of high-protein intake on bone turnover in long-term bed rest in women

Abstract

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. 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 1 of 2 groups. Control (CON) subjects (n = 8) received 1 g/(kg body mass·day) dietary protein. HiPROT subjects (n = 8) received 1.45 g protein/(kg body mass·day) plus an additional 0.72 g branched-chain amino acids per day during BR. All subjects received an individually tailored diet (before HDTBR: 1888 ± 98 kcal/day; during HDTBR: 1604 ± 125 kcal/day; after HDTBR: 1900 ± 262 kcal/day), with the CON group's diet being higher in fat and carbohydrate intake. High-protein intake exacerbated the BR-induced increase in bone resorption marker C-telopeptide (>30%) (p < 0.001) by the end of BR. Bone formation markers were unaffected by BR and high-protein intake. We conclude that high-protein intake in BR might increase bone loss. Further long-duration studies are mandatory to show how the positive effect of protein on muscle mass can be maintained without the risk of reducing bone mineral density.

Dietary acid load and bone turnover during long-duration spaceflight and bed rest

“…The literature on the effects of protein (type and amount) on bone are mixed, with some studies demonstrating that diets providing a high protein intake are detrimental to bone (28)(29)(30); conversely, many studies report high protein intake having a protective effect on bone (31,32). In light of our previous bed rest data showing that the ratio of dietary APro:K was positively associated with urinary NTX excretion (11), we hypothesized that a higher APro:K diet during spaceflight would yield a greater change in urinary NTX excretion than a diet with lower APro:K, and we hypothesized that diet would have no effect before flight.…”

Red risks for a journey to the red planet: The highest priority human health risks for a mission to Mars

“…Fish intake, likely secondary to omega-3 fatty acid intake, is beneficial for bone health 86 . Conversely, high intakes of dietary protein 87 , 88 , iron 89 and sodium 90 are detrimental to bone. The mechanism of the effect of protein and sodium on bone are likely similar, with both contributing to the acidogenic potential of the diet, leading to bone dissolution 91 , 92 .…”

“…Studies are underway between NASA and physicians at the Mayo Clinic in Minnesota to evaluate this further. If validated, women with PCOS might represent an analog population for astronaut ocular issues, and research to counteract this could benefit both populations 87 . This research may lead to the identification of one-carbon pathway genetic influences on cardiovascular function in astronauts (and women with PCOS).…”

Reduced energy availability: implications for bone health in physically active populations

“…Although research is ongoing, and far from conclusive, maintaining or relatively increasing protein intake has been suggested to be advantageous in preserving LBM during periods of energy deficiency, with intakes of 1.8–2.0 g kcal day −1 being recommended [ 103 ]. Theoretically, higher animal protein intakes could have a negative impact on bone, through increasing blood acidosis [ 104 ], which may subsequently increase osteocyte activity and bone resorption [ 105 , 106 ], as calcium may be released to buffer the increased acid load. That said, this might not be such an issue where calcium levels are adequate and so higher protein intakes should be accompanied by an adequate intake of calcium [ 107 ].…”