After minimum nitrogen requirements and minimum amino acid requirements have been established, studies will be directed toward investigating caloric restriction and adaptation to restriction of calories. It has been suggested that caloric restriction in animals and man results in apparent decreased energy need for the same activity. This apparent paradox has never been explained. It has been shown that there is adaptation to repeated episodes of caloric restriction both in animals and man, so that subsequent periods of caloric restriction result in decreased rate of weight loss, nitrogen loss, and longer survival. Additional experiments are urgently required to determine the metabolic demands for minerals—in particular, the metabolic balance of calcium, potassium, sodium, and phosphorus. Under conditions of high water consumption, large mineral losses are to be expected. Failure to replace these can cause an imbalance which could impair the efficiency of the individual to the extent of endangering the flight. Analysis of samples taken in flight, both of urine and feces, should be made. Respiratory quotients can be determined in flight, blood samples should be taken before and immediately after flight for analyzing selected components (in simulator studies these could be taken periodically), and nutritional intakes (which would be facilitated by formula diets) must be measured and analyzed. Short-Range Technology There are many practical difficulties in providing for food storage and accessibility in spacecraft. The packaging of food materials, both dehydrated and liquid, has proceeded satisfactorily under the supervision of the Food and Container Institute. If packaging materials are to be made to withstand very high relative humidities and large variations in temperature, additional investigations are required, since such containers are not yet available. In packaging, serious consideration must be given to the ease with which the food may be reached and eaten. If dehydrated formula foods are to be fed on short-term missions, additional work is required on the rehydration of such formulas. Present methods of water measurement under weightless conditions are not satisfactory, and better methods will have to be contrived. Long-Term Nutritional Problems