Nutrition is critical for health, both on Earth and during spaceflight. Specific nutrition concerns for spaceflight include adequate consumption of calories for energy, adequate fluid intake to prevent dehydration and renal stones, adequate calcium to minimize bone loss.
Dietary intake has been monitored on select Apollo, Skylab, Shuttle, and Shuttle-Mir flights as a part of scientific studies. Preflight and post flight intakes are determined using conventional methods for dietary assessment. Crew members are provided a diet-record logbook and digital scale, or the foods are weighed by the research dietitian and provided during each of the five- to eighteen-day data collection sessions. A variety of nutrient-analysis software programs are used. Crew members record their intake during space-flight by writing it in a log or, more frequently, they use a barcode reader that scans the food package label and then record the amount consumed. The amounts of certain nutrients in each meal are calculated from the record of how much of each type of food was eaten, plus knowledge of the amount of each nutrient in each type of food. Nutrient calculations using chemical analysis data for each spaceflight food item are performed after the flight. On the International Space Station, crew members complete a food-frequency questionnaire each week, and the data is down-linked for analysis. Dietary intake can thus be assessed in real time. Changes in diet may then be suggested to the crew members to prevent nutrient deficiencies.
A primary concern is that astronauts consume enough energy (calories) for optimal work performance and good health. Of the flight crews that have been monitored, only the Skylab crew members consumed enough energy—99 percent of their predicted intake. Most of the crew members in other flight programs consumed about 70 percent of what was planned. On the Skylab flights, much time and attention was given to eating and food preparation, and the crew members' extensive exercise program may have stimulated their appetite. On all other flights, the crew members have had a very busy schedule, with little time and attention devoted to eating.
Crew members' dietary intakes on Skylab, Shuttle, and Shuttle-Mir flights have tended to be higher in carbohydrate and lower in fat than their pre-flight intakes. This change may have been related to an abundance of foods high in carbohydrates, especially sugar-sweetened beverages, or perhaps these items are more easily prepared during a busy work schedule. Ample fat sources are available in the Shuttle food inventory—more than half of the main dish items contain greater than 30 percent of their calories as fat.
Intake of fluid should be about 2,000 milliliters (2 liters) per day, which is sufficient to prevent dehydration and kidney stone formation. Fluid intakes have varied from 1,000 to 4,000 milliliters per day, indicating that some crew members are getting less than the recommended amount.
Inflight sodium intakes of all crew members have exceeded the recommendation of less than 3,500 milligrams per day. Sodium intake is high because many of the "off-the-shelf" food items used have a high sodium content.
Calcium intakes have been below the recommended range of 1,000 to 1,200 milligrams per day. This level is estimated to minimize the bone mineral loss that occurs during spaceflight.
Iron intakes have been 50 to 60 percent greater than the recommendation of ten milligrams per day. As with sodium, iron intakes are high because the food items have already been iron-fortified. Too much iron in the body may cause tissue damage.
There seems to be an excess of both sodium and iron in the inflight diet, compared to predicted requirements. A food delivery system needs to be designed to include foods that will provide nutrients at the recommended levels, while providing variety and palatability to make eating more pleasant.
The International Space Station represents the beginning of an era of humans living and working in space, with the potential for a permanent human presence in space. Nutrition will play a vital role in ensuring the health and safety of space faring individuals, whether they are in low Earth orbit or on journeys to the moon, Mars, or beyond. A more complete understanding of the effects of spaceflight will not only help humans to explore the universe, but will provide information needed to maintain human health and treat diseases on Earth.