by

Paul C. Rambaut, Sc.D.^*

Malcolm C. Smith, Jr., D.V.M.

Harry O. Wheeler, Ph.D.

 

Lyndon B. Johnson Space Center

 

[277] The importance of nutrition in the adaptation of man to weightlessness was recognized long before the first Apollo flight. Nutrition remained a primary concern despite the fact that early projections of difficulties in swallowing, defecating, and urinating in weightlessness had proved unfounded. By the conclusion of the Gemini Program, space life scientists had noted several subtle changes with possible nutritional etiology.

Changes in musculoskeletal function appeared to be significant among these findings (Rambaut et al., 1973; Vogel et al., 1974). Prior to the first manned space flight, it had been suspected that the musculoskeletal system would be particularly susceptible to prolonged withdrawal of gravitational stress. Astronauts were subjected to a nullified gravitational field while they were confined in a vehicle in which mobility and physical activity were restricted. These conditions singly, or in combination, were expected to cause deterioration of bones and muscles.

The control studies by Deitrick, Whedon, and Shorr (1948) of the immobilization of four young, healthy men for as long as seven weeks clearly demonstrated that immobilization in body casts led to marked increases in urinary calcium. These levels more than doubled in five weeks and were accompanied by negative calcium balances as well as by related changes in nitrogen and phosphorus metabolism. In addition, a decrease in the mass and strength of the muscles of the lower extremities occurred, and deterioration in circulatory reflexes to gravity resulted within one week.

Other studies with immobilized subjects indicated that the clinical disorders most likely to be encountered during prolonged space flight are primarily a consequence of an imbalance between bone formation and resorption. As a result of these conditions, there is a loss of skeletal mass, which could eventually lead to hypercalcemia, hypercalciuria, osteoporosis, and possibly nephrolithiasis (Issekutz et al., 1966).

[278] Since the most meticulous work has disclosed that the greatest loss of calcium during bed rest is a result of increased urinary excretion, studies in which only urine calcium was measured are pertinent. The total evidence indicates that a one to two percent per month loss of body calcium is a reasonable prediction for persons in a weightless environment (Hattner & McMillan, 1968).

With the advent of space flight, additional studies have been performed on the effects of simulated weightlessness on skeletal metabolism. Graybiel and co-workers (1961) found there was no increase in urinary calcium excretion after one week of almost continuous water immersion. Negative balances of small magnitude and changes in bone density of the calcaneus during bed rest are indicated by Vogt and co-workers (1965).

The role of simulated altitude in modifying the metabolic effect of bed rest has been investigated (Lynch et al., 1967). In a study of 22 healthy men, four weeks of bed rest at ground-level atmospheric pressure conditions resulted in expected increases in urinary and fecal calcium and in urinary nitrogen, phosphorus, sodium, and chloride. In similar metabolic studies performed with another 22 subjects at bed rest at simulated altitudes of 3000 and 3700 meters, urinary calcium losses were significantly less as the altitude increased (Lynch et al., 1967). Urinary losses of phosphorus, nitrogen, sodium, and chloride were less at a simulated altitude of 3700 meters than they were during bed rest studies at ground level. Results of these studies indicate that diminished atmospheric pressure, or perhaps a decreased partial pressure of oxygen or a change in pH, may have a preventive effect on mineral loss from the skeleton. Limited data available from inflight studies tend to support the use of immobilization as a terrestrial model to simulate alterations in calcium metabolism during space flight. During the 14-day Gemini 7 flight, loss of calcium occurred in one of the two astronauts, and the changes in phosphorus and nitrogen balance also indicated a loss of muscle mass (Lutwak et al., 1969; Reid et al., 1968).

As evidenced from bed rest studies lasting from 30 to 36 weeks, mineral losses are likely to continue unabated during prolonged space flight. In balance studies (Vogel & Friedman, 1970; Donaldson et al., 1970), calcium losses from the skeleton during bed rest averaged 0.5 percent of the total body calcium per month. In the same subjects, tenfold greater rates of localized loss from the central portion of the calcaneus were detected by gamma-ray-transmission scanning.

lnflight weight losses were experienced throughout Project Mercury, Gemini, and the Apollo missions. Such weight losses were attributed, in part, to losses in body water. Since weight was not regained completely in the 24-hour period immediately postflight, it was probable that tissue had also been lost. What part of these losses was brought about by insufficient caloric intakes was unknown.

Speculation on the theoretical energy requirements of man during space flight began before the United States Project Mercury and the Soviet Vostok flights. At one time, it had seemed logical to assume that activity in a weightless environment would require less energy than at one g because work associated with counteracting the force of gravity would be eliminated However, caloric requirements are affected by numerous variables including age, physical and mental activity, stress, body size and composition, together with relative humidity, radiation, pressure, and environmental temperature. During the [279] Apollo missions, therefore, the question of inflight caloric requirements was explored in much greater depth

Metabolic changes in addition to they associated with an inadequate intake of energy were also elucidated during the Gemini Program. The possibility remained that space flight conditions would exert exaggerated demands on the micronutrients and would thus lead to some marginal deficiency state. It is believed that Soviet nutritionists provided their crewmen with elevated quantities of water-soluble vitamins, and that they had observed increased destruction of the B vitamins under conditions of prolonged low frequency vibration of test subjects. These observations were not confirmed during the Gemini Program. However, because alterations were seen in red cell mass and plasma volume, the vitamin E content of the diet in the presence of the hyperoxic Gemini spacecraft atmosphere was questioned (Fischer et al., 1969).

The development of future space food systems necessitated an accurate knowledge of inflight human nutrition requirements. Food systems having minimum weight and minimum volume are required for space flight (Heidelbaugh et al., 1973). For this reason, the Apollo foods were generally dehydrated and formulated to occupy little volume. The nutritional consequence of these measures was a matter of continuing interest in the Apollo Program.

Food Analysis

With very few exceptions, all foods used during the Apollo Program were analyzed for nitrogen, fat, carbohydrate, crude fiber, calcium, phosphorus, iron, sodium, potassium, and magnesium content. Some composite Apollo menus were analyzed for water- and fat-soluble vitamins. It was not always feasible to analyze the same lot of food that was actually used during the mission, and the variation in analytical values from one lot to another and from one item to another must be considered when the intake data are reviewed.

Dietetics

The menus used by the Apollo astronauts were formulated from flight qualified Apollo foods in combinations that complied with the personal preferences of the crewmen and that met the Recommended Daily Dietary Allowances (NAS, NRC, 1968). The menus were primarily composed of dehydrated foods that could be reconstituted before eating. The foods were consumed in a prearranged sequence but could be supplemented by a variety of additional items that were packaged in am individually accessible form.

Nutrient Intake Measurements

The quantity of individual nutrients consumed during all Apollo missions is presented in table I as a composite estimate derived from numerous measurements. The crewmen were provided with prepackaged meals that were normally consumed in a numbered sequence. Foods omitted or incompletely consumed were logged. During the Apollo 16 [280] and 17 missions only, these deviations from programmed menus were reported to flight controllers in real time. Snack items consumed that were not in the programmed prepackaged menus were also recorded in the flight logs. On all Apollo flights, most food residue and unopened food packages were returned; the residue was weighed only to provide more precise information on inflight food consumption and to verify inflight logging procedures. For the Apollo 16 and 17 missions, nutrient intake information was obtained for 72 hours before flight and for approximately 48 hours after flight.

For the Apollo 17 mission, a five day metabolic balance study was performed approximately two months before the mission by using the flight menus and collecting urine and fecal wastes. Low residue diets were generally used commencing three days before each Apollo flight in order to reduce fecal mass and frequency during the first few days of flight.

Fecal Measurements

Fecal samples were returned from all Apollo flights and analyzed for a variety of constituents either by nuclear activation analysis or by wet chemistry techniques.

Metabolic Balance

Analysis of blood obtained postflight on early Apollo missions, together with certain endocrinological and electrocardiographic changes in Apollo 15, made it desirable to measure urine volume and bring back samples of urine on Apollo 16. During this mission, it was also possible to continue to return fecal samples and to continue to measure nutrient intake. Sufficient data were therefore available to conduct a partial metabolic study.

[281] For a more detailed metabolic balance study in conjunction with Apollo 17, accurate measurements of fluid intake and output were performed approximately two months before the mission. A five-day food compatibility/metabolic study was performed in which the three Apollo 17 prime and backup crewmembers consumed their flight foods, and metabolic collections were performed. The study was designed to obtain baseline data on the excretory levels of electrolytes and nitrogen in response to the Apollo 17 flight menus. The crewmembers consumed the flight menu foods for five complete days. During the last three days of this test, complete urine and fecal collections were made.

Beginning 64 hours before Apollo 17 lift-off and continuing throughout the mission until 44 hours following recovery, all food and fluid intake was measured. For the Lunar Module Pilot, these collections continued until suit donning; for the Commander and the Command Module Pilot, collection continued until approximately 12 hours before lift-off. All urine was collected, measured, sampled, and returned for analysis. Urine was collected before and after flight in 12-hour pools. Complete stool collections were performed.

All deviations from programmed food intake were logged and reported. All foods were consumed according to preset menus arranged in four-day cycles. Every food item used during the flight was derived from a lot of food that had been analyzed for the constituents to be measured. Inflight water consumption was measured by use of the Skylab beverage dispenser. During the preflight and postflight periods, conventional meals were prepared in duplicate for each astronaut. One duplicate of each meal was analyzed in addition to the residue from the other duplicates to measure intake and output.

Apollo 17 inflight urine samples were collected by means of a biomedical urine sampling system (BUSS). Each BUSS consisted of a large pooling bag, which could accommodate as much as four liters of urine collected during a day, and a sampling bag, which could accommodate as much as 120 cc. The BUSS was charged with 30 mg of lithium chloride. The lithium chloride concentration in the sample bag was used as a means of determining total urine volume. Each BUSS also contained boric acid to effect stabilization of certain organic constituents.

The inflight urine collection periods began with suit doffing at approximately 00:07:00 ground elapsed time (GET). The collection periods were the times between scheduled effluent dumps and were approximately 24 hours each. During undocked flight of the Command Module, urine was collected only from the Command Module Pilot. During periods in which the crewmen were suited, urine was collected in the urine collection and transfer assembly and subsequently dumped overboard without sampling. However, urine collected in the Commander and Command Module Pilot assemblies during the Command Module extravehicular activities (255:00:00 to 260:00:00 GET) was also returned. For the Apollo 17 mission, the periods during which urine was not collected are as follows:

1. Commander and Command Module Pilot-lift-off to suit doffing (00:00:00 to 00:07:00 GET)

2. Command Module Pilot - Lunar Module activation and lunar descent (108:00:00 to 114:30:00GET)

3. Command Module Pilot-rendezvous (187:00:00 to 195:00:00 GET)

[282] 4. Commander and Lunar Module Pilot-Lunar Module activation, lunar descent, lunar surface operations and rendezvous (107:00:00 to 208:00:00 GET)

Urine collected from the Commander and the Command Module Pilot from rendezvous to the beginning of the first collection period after rendezvous (approximately 197:00:00 to 208:00:00 GET) was also dumped directly overboard.

Each BUSS was marked with the name of the crewmember and the ground elapsed time of collection. Following each collection period, the urine pool was thoroughly mixed before a sample was taken. The urine samples represented a 24-hour void and were subsequently analyzed for electrolytes, nitrogen, and creatine.

All fecal samples collected from each crewmember for the following periods were returned: beginning 64 hours before lift-off, during the mission, and for 44 hours after the flight. Inflight fecal samples were chemically preserved for storage in the spacecraft.

Body Volume Measurements

For the Apollo 16 crewmembers, a measurement of body volume was made by stereophotogrammetry, using a special computer program, three times before the flight and three times after the flight (Peterson & Herron, 1971). Body density was calculated from body volume and weight. Density was used to calculate the percentage of fat by means of the following formula.

Changes in calculated lean body mass and total body fat were converted into caloric equivalents by means of standard values of 37.6 kJ/gm^** for fat and 16.7 kJ/gm for protein.

Total body water was measured by means of potassium-42 dilution (Johnson et al, 1974) Lean body mass was calculated as follows

The nutritional composition of the typical Apollo inflight diet is given in table 2 This diet, which is characteristically high in protein and carbohydrate and low in residue and fat, was not necessarily consumed by all astronauts in its entirety.

A typical Apollo diet was analyzed for vitamins, and results were compared with Recommended Daily Dietary Allowances (NAS, NRC, 1968). The data indicate the Apollo diet provided an excess of some vitamins (A, E, C, B₁₂, B₆, and riboflavin) and marginal amounts of others (nicotinate, pantothenate, thiamine, and folic acid).

The average intake of protein, fat, and carbohydrate for the Apollo 7 through 17 crewmen is given in table 3. Fiber intake measurements are given for the Apollo 12, 15, 16, and 17 missions.

The quantity of energy supplied by dehydrated food for the Apollo 15 to 17 missions is given in table 4. The average energy intake of each Apollo crewmember is given in table 5. These energy values were calculated from the composition of the food consumed. Average energy intakes expressed on the basis of body weight are given in table 6. For comparison, the average energy intake of selected Apollo crewmembers during a mission and on the ground is given in table 7.

The average intakes of calcium, phosphorus, sodium, and potassium for each Apollo crewman are given in table 8. Diets for the Apollo 16 and 17 missions were fortified with potassium gluconate. The contribution of supplementary potassium gluconate to the total intake for the Apollo 15, 16, and 17 crewmen is given in table 9.

Inflight fecal samples were analyzed for inorganic constituents using nuclear activation analyses and wet chemistry techniques. The findings were summarized by Brodzinsky and co-workers (1971). Inflight fecal samples were also analyzed for total fat, fatty acids, and conjugated and unconjugated bile acids (tables 10 and 11). Data on fat absorption in flight (Apollo 16 and 17) are given in table 12.

Apollo 16 Metabolic Study

The input and output of various elements, particularly potassium, were carefully examined in the Apollo 16 balance study and a detailed assessment of energy metabolism was made (Johnson et al., 1974). The average daily inflight potassium intake for the Commander was 113.6 milliequivalents. During the mission, potassium was lost by the fecal route at a rate of approximately 6.4 mEq/day, whereas approximately 18.8 mEq/day were lost before the flight and 20.5 mEq/day after the flight. During the mission, absorbed potassium levels were 107.2 mEq, whereas preflight and postflight levels were 94.8 and 77.6 mEq, respectively. During the extravehicular and lunar surface periods, the Commander consumed a maximum of 152.4 mEq daily.

The average daily inflight potassium intake for the Lunar Module Pilot was 114.7 mEq, compared with an average daily preflight intake of 110.5 mEq and an average daily postflight intake of 97.5 mEq. During the preflight, inflight, and postflight phases, the average daily fecal losses were 33.5, 11.1, and 31.0 mEq, respectively. The absorbed daily potassium levels for preflight, inflight, and postflight phases were 77.0,103.6, and 66.5 mEq, respectively. Although these levels were less than the recommended levels of 150 mEq per day, they were adequate for ground-based requirements. A peak level of 148 mEq per day was consumed by the Lunar Module Pilot during lunar surface activities.

* Mean value is 154.7 ± 18.4 kJ/kg (37.0 ± 4.4 kcal/kg)

**Mean value is 110.8 ± 13.8 kJ/kg (26.5 ± 3.3 kcal/kg)

For the Command Module Pilot, average daily preflight, inflight, and postflight dietary potassium intakes were 94.3, 79.9, and 82.4 mEq, respectively. Fecal samples for the same periods indicated that potassium levels were 27.6, 6.3, and 26.2 mEq, respectively. Available daily preflight, inflight, and postflight potassium level- were, therefore, 66.7, 73.6, and 56.2 mEq, respectively.

Input and output data on sodium, chloride, and calcium levels for the Apollo 16 crewmembers are summarized in table 13.

In the analysis of the balance study performed for the Apollo 17 mission, inflight metabolic data were compared with those obtained during the five-day control study conducted approximately two months prior to flight. Rigorous intake and output measurements were accomplished immediately before the flight and after the flight to detect gross changes; however, the duration of these periods was not sufficient to establish reliable metabolic baselines.

For the Apollo 17 Command Module Pilot, water consumption from all sources was considerably lower during the flight than during the control balance study (table 14). Inflight urine outputs were also proportionately lower for all three crewmembers than those established during the control study. When the conditions of temperature and humidity that prevailed during the flight are considered, it is estimated that in insensible water loss of 900 to 1200 cc/day occurred. This loss was equivalent to the preflight loss. Total body water measurements also did not support the tendency toward negative water balance (see Section III, Chapter 2, Clinical Biochemistry).

Based on numbers adjusted for equilibrium during the control phase and insensible losses, all three crewmembers were in negative calcium balance during the inflight period (table 14). The negative balance was particularly pronounced for the Command Module Pilot. For two of the crewmembers, the negative calcium balance persisted after the flight. All crewmembers had exhibited a pronounced positive balance during the five-day control period study possibly because the flight diets contained a higher calcium level than did the customary daily intake of these crewmembers (table 14). As can be expected from the negative calcium balance, phosphorus balance was generally negative during the flight.

All three crewmembers demonstrated a sustained negative nitrogen balance during the flight (table 14). Occasional negative nitrogen balances of small magnitude were also detected before the flight. Diminished nitrogen retention is supportive evidence for the....

*1 kcal = 4.184 kJ

[291] ....general musculoskeletal deterioration noted on previous flights and during ground-based hypokinetic simulations of flight-type conditions.

Sodium intakes during the flight were all less than 250 mEq/day. Intake and output measurements for sodium indicated positive balances for this element during the flight for all three crewmembers (table 14). However, sodium output in sweat was not measured and this route of excretion could have accounted for all the apparent "positive balance" and even have resulted in a slight negative balance for sodium. Sodium balance was positive during the flight for all three crewmembers (table 15) if insensible losses are neglected.

In compliance with previous recommendations based on observed inflight potassium deficits, inflight potassium intakes were maintained above normal ground-based intakes (73 to 97 mEq/day) (table 15). Potassium retention during the flight was significantly less than that established during the control study. A summary of overall metabolic balance for Apollo 17 crewmembers with all numbers adjusted to reflect equilibrium during the control period is presented in table 15.

Anthropometric Measurements

A summary of body weight changes based on the mean of the weights on 30,15, and 5 days before lift-off compared to those obtained immediately after recovery is presented in table 16. The weight changes during the 24-hour period immediately following recovery are also given.

Body volume was measured before and after the Apollo 16 mission by stereophotogrammetry. An analysis of densitometric data is presented in table 17.