The proportions of carbohydrate, fat and protein in space feeding

Most of the weight of food supply is due to the need for energy. Fat is most efficient because it has a higher ratio of carbon and hydrogen to oxygen than do protein and carbohydrate, so stored food systems for long missions would logically rely heavily on this form of calories. Biological systems proposed for atmosphere regeneration yield potentially edible products quite high in protein, whereas chemical systems provide carbohydrate as sugars and alcohols if they produce food at all. There is a minimum need for all three forms to fulfill essential nutrient functions besides energy. These minimal needs are reasonably well known, but only for short times in terrestrial environment. Lower limits, thought to be about 45 g protein, 7 g fat, and 70 g carbohydrate, may need to be increased somewhat in space due to altered oxygen concentration, hypokinesia and other stresses. Upper limitations are less clearly established, even for earth environment. High intakes of protein result in increased water requirement, loss of minerals (correction of minierals) and excessive urinary uric acid. Intestinal absorption and metabolic capacity for fat are known to be limited. Although carbohydrate is usually quite innocuous, some forms are not well tolerated in high concentration. Provisional allowance ranges are, in % of total calories: 8-50 protein, 2-75 fat and 10-90 carbohydrate.