Stein T P
Department of Surgery, University of Medicine and Dentistry of New Jersey - SOM, 2 Medical Center Drive, Stratford, NJ 08084, USA.
Nutr Res Rev. 2001 Jun;14(1):87-118. doi: 10.1079/NRR200119.
Space flight is a new experience for man. Tension on the weight-bearing components of the musculo-skeletal system is greatly reduced, as is the work required for movement. The body responds by a reductive remodelling of the musculo-skeletal system. Protein is lost from muscles with anti-gravity functions. The rate of Ca loss from the weight-bearing bones is about 1 % per month. Voluntary dietary intake is reduced during space flight by about 20 %. These adaptations to weightlessness leave astronauts ill-equipped for life with gravity when they return to earth. Rates of energy expenditure are similar to that expected on the ground for comparable activities. Protein intake is adequate in flight but may be limiting after space flight due to substrate competition between repleting muscle and other anabolic processes. The most serious nutritional problem is the inability to maintain energy balance on missions with high exercise requirements. The poor dietary intake is probably a consequence of engineering-imposed environmental constraints. The low levels of lighting in the space vehicle may not be enough to promote vitamin D synthesis. Nevertheless, the evidence suggests that a normal well-balanced diet with plenty of fluids will be as healthy in space as on earth. The long-term goal of the manned space programme is to develop the means of sustaining human life beyond earth. This will involve the development of technologies to grow food, maintain a breathable atmosphere and recycle waste products with the only external input being energy.
太空飞行对人类来说是一种全新的体验。肌肉骨骼系统的承重部件上的张力大幅降低，运动所需的功也是如此。身体通过对肌肉骨骼系统进行还原性重塑来做出反应。具有抗重力功能的肌肉会流失蛋白质。承重骨骼的钙流失率约为每月1%。太空飞行期间，自愿饮食摄入量减少约20%。这些对失重的适应性变化使宇航员返回地球后难以适应有重力的生活。能量消耗率与在地面上进行类似活动时预期的水平相似。飞行期间蛋白质摄入量充足，但太空飞行后可能会受到限制，因为补充肌肉和其他合成代谢过程之间存在底物竞争。最严重的营养问题是在对运动要求较高的任务中无法维持能量平衡。饮食摄入不足可能是工程环境限制造成的后果。航天器内的低光照水平可能不足以促进维生素D的合成。然而，有证据表明，营养均衡且富含大量液体的正常饮食在太空中与在地球上一样健康。载人航天计划的长期目标是开发在地球以外维持人类生命的方法。这将涉及开发种植食物、维持可呼吸的大气以及回收废物的技术，唯一的外部输入是能量。
