Nutritional biochemistry of space flight

Humans have flown in space for more than 35 years. Since that time, Americans have walked on the moon, launched two space stations (Skylab and the International Space Station), docked during orbit with a Soviet Soyuz space capsule and the Russian Mir space station, flown the only reusable space vehicle, and visited a Russian space station for more then 6 months at a time. Nutritional intake has not been considered a high priority during relatively brief flights of the Space Shuttle and other programs (i.e., less than 21 days). However, as we embark on extended-duration (i.e., > 30 days up to several years) missions, nutrition becomes a critical issue. The impact of weightlessness on human physiology is profound. We are in the very early stages of understanding how space flight affects nutrient requirements and related issues such as absorption, metabolism, and excretion. Apart from the obvious role of providing energy and required nutrients, nutrition is also important in terms of enhancing psychosocial interactions among crews, and ameliorating some of the effects of microgravity on the body (i.e., acting as a "countermeasure"). The interrelationships among space flight, nutrition, and physiology suggest that a program of specified nutritional intake may be required to enhance mission safety and crew productivity. Defining which nutrients are essential for the space flight environment depends on a more complete understanding of how weightlessness affects physiology. Providing the required nutrients is also limited by the types of foods that can be provided by the food system on board the space craft, and the dietary habits of space crews.