Nutrition in Space: What Astronauts Eat
Astronauts lose significant amounts of bone mass, muscle mass, and blood volume during space travel. Here's how the experts are trying to make space food more tasty and nutritious.
Sometime within the next 20 to 30 years, a small group of men and women is expected to be sent on a three-year space mission to Mars. The big question: What to eat?
Among the foods almost sure to be included by NASA in the diets of the half dozen or so astronauts who'll be hurled along the 90-million-mile trajectory toward the red planet: Little Debbie brownies, Lorna Doones, Planter's peanuts, Keebler butter crackers, and m&ms—both plain and peanut. "The coating keeps them from getting messy if they melt," explains Vickie Kloeris, NASA's technical manager for shuttle and station food systems.
What happened to all the Cheez-Whiz-like goop associated with space flight that the astronauts squeezed directly into their mouths? And the Tang?
They still use Tang, Kloeris notes. And Kool-Aid and Country-Time Lemonade. But everything out of a tube or in the shape of a cube? That's so moon-walk.
"Toothpaste tubes of chicken salad went out back in the Apollo days," comments Scott M. Smith, lead scientist for the nutritional biochemistry laboratory at Johnson's Space Center in Houston. "Today, we try to come up with a food system that's as much like the way you and I eat as possible." The astronauts, he says, "do eat food that looks like food."
Offering Appealing Food
The move toward more palatable meals is critical. There's a lot of "not eating" on space flights, as Kloeris puts it. The astronauts lose weight. "On long flights," she says, "some have consumed only about 50% of caloric requirements. The more appealing we can make the food system, the more tempted they're going to be to eat—and to eat enough calories."
Why astronauts tend not to eat enough isn't entirely clear. When they're asked, Kloeris reports, they say things like, "'Well, you know, I just wasn't hungry.'"
Part of it, presumably, is that eating takes more time than on the ground. Then, too, space foods generally lack variety in terms of texture and aroma, leading to "taste monotony," report Smith and Dr. Helen W. Lane, chief nutritionist and manager of university research and affairs at the Johnson Space Center.
Finding New Ways to Feed Astronauts
To help get around that, NASA hopes to increase the food list for the astronauts making the six-month journey to Mars. (They'll spend about a year and a half there and then another six months flying back, for a total of three years away from Earth.)
Scientists are also trying to find ways for astronauts to "farm" foods in flight so that they can have perishables such as fresh fruits and vegetables.
Another goal is to include a refrigerator and freezer on the space craft, which will require technical considerations in terms of the weight of the fridge, the energy used to power it, and the space it will take up on board. Currently, space ships have ovens but no facilities for keeping foods cold, which cuts down on the types of items that can be included on a trip. Everything has to be shelf stable, which includes foods such as soups and stews, Del Monte canned fruits with flip-top lids, puddings that come in those little white tubs with foil laminate pull-off covers, dried fruits, and trail mix—but no fresh, crunchy vegetables, and no dairy items that haven't been heavily processed.
"Yes, we have powdered cheese sauces in a lot of our products," Kloeris notes. "But people like to be able to eat a piece of cheese," which can't be on board without a refrigerator.
The foods that are available tend to be awfully warm, which can take away from their appeal. The temperature of the food trays, Kloeris says, is usually between 75° to 80°F—a little higher than the cabin temperature in general. That's because right behind where the food is kept are "a bunch of electronics that help power the shuttle," she notes.
Combatting Bone Loss
Sending a refrigerator to Mars isn't just about getting the astronauts to eat by breaking the boredom and monotony. There are also nutrition considerations. One is that shelf-stable foods, unlike refrigerated and frozen foods, require a lot of ]]>sodium]]> . That's generally the preservative that keeps them stable, in fact. (Think of how canned vegetables and other canned foods tend to contain much more sodium than fresh or frozen.)
The thing is, there's evidence from a number of studies looking into people's food consumption here on Earth that the more sodium in the diet, the greater the loss of ]]>calcium]]> from bones. That's a particular problem for astronauts because bone loss during space flight is greatly accelerated. The natural loss of bone in an aging group of people is about 1% a year, Smith says. But in space flight, the loss, on average, is about 1% a month. The bone loss starts within hours of weightlessness, particularly in the weight-bearing bones of the ankles, hips, and spine.
Cutting sodium from the astronauts' diets may help to slow the bone loss, at least to some degree. Observations of crew members of the Soviet Mir space orbiter showed they consumed about 4,000 milligrams of sodium per day—nearly twice the 2,400-milligram daily maximum recommended for Earth dwellers by the National Academy of Sciences.
Astronauts also have to be given supplements of ]]>vitamin D]]> , without which bone-building calcium cannot be properly absorbed. The supplemental vitamin D is necessary because most of our D is manufactured in the skin upon exposure to the sun's rays, but the space ship prevents those rays from reaching the crew's bodies. Supplemental ]]>vitamin K]]> is also necessary to help slow the bone loss, though researchers have yet to determine to most effective solution.
Combatting Radiation Bombardment
Ironically, while the beneficial D-producing rays are kept from reaching the crew, being out of the Earth's protective atmosphere during space flight causes tremendous exposure to radiation from the sun that can engender oxidative damage to cells and, ultimately, ]]>cancer]]> .
"One of the big show stoppers is radiation," says William Evans, former leader of nutrition, physical fitness, and rehabilitation for the National Space Biomedical Research Institute.
"What we're attempting to do right now," Evans says, "is come up with an ideal cocktail of antioxidants" that can fight off the oxidative havoc. It may also include some ]]>soy]]> products, he says, along with nutrients like vitamins C and ]]>E]]> . The isoflavones contained in soy may help protect the body's cells from damage.
Joanne Lupton, current leader of nutrition, physical fitness and rehabilitation team, is looking specifically at ways to reduce the astronauts' risk for ]]>colon cancer]]> , the second leading cancer killer in the United States. One possibility is feeding the Mars crew adequate amounts of ]]>fish oil]]> in combination with ]]>fiber]]> .
There's "oxidative damage to cells from radiation," she points out. If that damage "forms a mutation in the cells, then a cancer" could develop. "How can you stop the initial damage?"
Fish oil, Lupton says, can potentially prime the cell membrane to signal to the rest of the cell that it should undergo apoptosis, or programmed cell death. That would keep the faulty cell from multiplying and forming a cancerous mass.
But the fish oil just readies the cell for suicide; it doesn't actually cause the death. That's where the fiber comes in. You eat the fiber, it goes into the colon, and then microflora in the colonic "tube" feed off of it. As a result of that feeding, the microflora produce short-chain fatty acids, one of which is called butyrate. That's the substance that actually initiates cell death.
"For a time, they didn't want to feed astronauts fiber," Lupton says. The feeling was that it would just create "more fecal material that they would have to deal with." So the astronauts were down to one gram or even zero grams of fiber a day. (Americans typically consume about 15 grams daily; the recommended amount is 25 grams.) Then "the astronauts complained," Lupton notes. "They said they were ]]>constipated]]> . Fiber was reintroduced."
Whether they'll eat the 20 to 25 grams that would appear to be enough for initiating the death of mutated cells, should it be necessary, Lupton isn't sure. Furthermore, she says, "The whole mechanism isn't worked out." At this point it's a hypothesis based on preliminary research. But the potential interaction between fish oil and fiber bears further investigation, she comments.
Combatting Too Much Iron, Too Little Muscle Mass
"One of the big things that happens during space flight is that we lose about 20% of blood volume," Evans says. The fluid part of blood gets excreted in the urine. To compensate, the body reduces its number of red blood cells, which contain ]]>iron]]> . With less iron needed for blood cells, more is left free-floating, so to speak. And that could potentially induce a kind of iron overload that results in possible organ damage, similar to the way in which the genetic iron-overload disease ]]>hemochromatosis]]> "rusts away" the body's internal organs.
Currently, menus on space flights provide enough iron for astronauts to consume more than 20 mg a day—twice the 10-mg recommended allowance for men and 50% more than the 15 mg advised for women of childbearing years.
"We worry about people getting too much iron," Smith says. NASA will look at astronauts' iron status more closely in the future.
Another problem is loss of muscle mass, which, like loss of bone mass, results from the weightlessness of flight. (The fact that the force of gravity on Mars is only about one-third the gravity pull on Earth doesn't help.) The legs present a special concern. On a long space flight, there can be up to a 10% loss in calf-muscle volume.
To help minimize muscle shrinkage, says Evans, "We've proposed a supplement of essential amino acids to stimulate muscle protein synthesis. If amino acid supplements do [the trick]," Evans comments, "they may be something to give to older people. Many older people eat marginal amounts of protein," often because they eat small amounts of food. They also experience muscle atrophy. The supplements may help them maintain muscle mass as they age.
The current recommended allowance for protein is 0.36 g for every pound of body weight. But that might not be enough for either older people or astronauts, Evans points out. The results of new studies should potentially help clarify the protein needs of both the older population and space travelers. Space flight "speeds up aging," Evans notes—accelerated bone loss, accelerated muscle loss, greater chance of cell mutations that can lead to cancer. Whatever we learn about the nutrient needs of one population will help us adjust the recommendations for the other.
Of course, concrete answers are a number of years off. And even when they do come in and NASA figures out such things as how to ship a fridge to Mars and how to grow food on board a spacecraft, eating off-planet will probably never be quite the same as eating in your own kitchen. Why?
About 50% of the food is freeze-dried, Smith reports, including some items like chicken, beef, and fish. "The astronauts plump it up to regular food."
The reason for all the freeze-dried products is that water for plumping can be made in outer space, which amounts to a significant weight savings in terms of getting the spacecraft off the launch pad. Kloeris explains that the fuel cells—or big batteries—used to run the spaceship combine hydrogen and oxygen to make electricity. One of the byproducts is H 2 O, or water. There's actually "an abundance of water available," Kloeris notes. It's "kept in holding tanks."
Having Special Snacks
The idea of a largely freeze-dried menu may not sound very appealing. However, there are some compensations for having to deal with a meal plan that contains items such as reconstituted turkey breast.
One is that if an astronaut doesn't like, say, m&ms or Lorna Doones (which come in their Earthly forms), he or she can request some "off-menu" favorites to take on board. That is, reports Kloeris, if a space traveler wants to satisfy an occasional hankering for a Chips Ahoy! cookie or a Snicker's bar, chances are she will have that opportunity.
Then, too, the Tang in space doesn't only come in orange. You can also get flavors that are not traditionally marketed in the United States, like mango.
Not the ultimate in haute cuisine, perhaps. But the view should be spectacular.
National Aeronatics and Space Administration
Canadian Council on Food and Nutrition
Heer M. Nutritional interventions related to bone turnover in European space missions and simulation models. Nutrition. 2002;18:853-856.
Iwamoto J, Takeda T, Sato Y. Interventions to prevent bone loss in astronauts during space flight. Keio J Med. 2005;54:55-59.
Space food. NASA facts. NASA website. Available at: http://spaceflight.nasa.gov/spacenews/factsheets/pdfs/food.pdf . Accessed October 18, 2007.
The zero gravity diet. Science News website. Available at: http://www.sciencenews.org/articles/20050312/food.asp . Accessed October 18, 2007.
Last reviewed May 2009 by ]]>Maria Adams, MS, MPH, RD]]>
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