Eating Healthy in Zero Gravity: Nutrition During Space Flight
Here on Earth, there is amazing variety in the types of foods people eat. Astronauts don’t have this luxury. Their food must be storable, transportable, and compact, and still provide all the nutrients needed to sustain life, especially during the longer missions. Taste may be a priority; think of living off plane food for months at a time. In the most recent issue of Advances in Nutrition, Lane et al. describe some of the nutrition issues that arise during space travel.
The first consideration is energy. Does our metabolic rate change when in space? Food intakes during space flight are generally lower than on Earth however experiments with doubly-labeled water found that there is no difference in metabolic requirements. Total energy use may even be higher in space due to increased exercise. Perhaps a calorie deficit is the reason behind astronauts’ documented weight loss during a mission. The authors also discuss the palatability of space food, which may be a cause of lower food intakes and weight loss (see article by Matsumoto and colleagues).
One common problem for astronauts is that they lose both muscle and bone during their time in the micro-gravity of space. The chance of osteoporosis and bone fractures on their return to Earth is high. It seems that gravity helps to keep both muscle and bone strong. To compensate for a lack of gravity in space, astronauts perform resistance exercise with specialized equipment such as NASA’s Advanced Resistance Exercise Device (ARED). Orwoll and co-workers report that the ARED attenuated reductions in bone mineral density that usually occur during extended space travel. Adequate levels of protein, total energy and vitamin D are essential to maintain both bone and muscle, as reported by Smith and associates. In addition, the salt content of astronaut foods has been reduced in recent years; high sodium levels increase bone resorption rates. Instead of around 5300 mg per day sodium, the content in foods was reduced to 3000 mg, somewhat closer to the recommendations on Earth (USA) of 2300 mg per day.
Vision problems are also common in a subset of astronauts. It was found that people who had low folate, high homocysteine and high methylmalonic acid concentrations prior to space flight were at enhanced risk of ophthalmic changes (Zwart et al.). This was considered to be an interaction between genetic polymorphisms for genes involved in one-carbon metabolism interacting with the micro-gravity of space.
Innovative new food processing techniques have improved the palatability of food provided on space missions. Early flights in the 1960s used primarily dried food that was reconstituted. By the time of the Apollo missions starting from the 1960s, thermo-stable pouches, canned and freeze-dried foods were available. The Skylab had a fridge and freezer, allowing astronauts the ability to eat cooled and frozen foods. Newer fuel cells that produce water as a waste product have meant that re-hydrated food is used exclusively during newer missions, albeit with a much larger selection than was available previously. Astronauts are also given the opportunity to choose main meals directly before they consume them, rather than 6 months before a mission (the Smithsonian Museum has an interesting article on atronauts’ actual menu items).
It is clear that providing food for astronauts does more than just put food in their stomachs. Good nutrition is as important to the successes of a space mission as astronauts’ training or awe-inspiring technology that gets them there.
Helen W. Lane, Charles Bourland, Ann Barrett, Martina Heer, and Scott M. Smith. The Role of Nutritional Research in the Success of Human Space Flight. Adv Nutr September 2013 4 5): 521-523; doi:10.3945/an.113.004101 http://advances.nutrition.org/content/4/5/521.short
Matsumoto A, Storch KJ, Stolfi A, Mohler SR, Frey MA, Stein TP. Weight loss in humans in space. Aviat Space Environ Med. 2011 Jun;82(6):615-21. http://www.ncbi.nlm.nih.gov/pubmed/21702312
Orwoll ES, Adler RA, Amin S, Binkley N, Lewiecki EM, Petak SM, Shapses SA, Sinaki M, Watts NB, Sibonga JD. Skeletal health in long-duration astronauts: nature, assessment, and management recommendations from the NASA Bone Summit. J Bone Miner Res. 2013 Jun;28(6):1243-55. doi: 10.1002/jbmr.1948. http://www.ncbi.nlm.nih.gov/pubmed/23553962
Smith SM, Heer MA, Shackelford LC, Sibonga JD, Ploutz-Snyder L, Zwart SR. Benefits for bone from resistance exercise and nutrition in long-duration spaceflight: Evidence from biochemistry and densitometry. J Bone Miner Res. 2012 Sep;27(9):1896-906. doi: 10.1002/jbmr.1647.
Zwart SR, Gibson CR, Mader TH, Ericson K, Ploutz-Snyder R, Heer M, Smith SM. Vision changes after spaceflight are related to alterations in folate- and vitamin B-12-dependent one-carbon metabolism. J Nutr. 2012 Mar;142(3):427-31. doi: 10.3945/jn.111.154245. Epub 2012 Feb 1.