5.8 group which requires the highest adult nutrition. Pregnant and lactating women require increases in all the nutrition levels listed. Children and adolescents require higher levels in some categories, particularly protein, calcium, and iron. Persons ill or recovering from illness require higher dietary allowances as well. Table 5.2 does not suggest a carbohydrate content because wide variations in carbohydrate levels do not affect health. Diets on Earth range from 20% to 80% carbohydrates. The 20% value is a minimum since carbohydrates provide bulk necessary for the proper function of the digestive system. Also not in Table 5.2 is a requirement for unsaturated fatty acids particularly of the linoleic series which cannot be synthesized from other foods by the human body. In 1948 the Food and Nutrition Board recommended that 20%-25% of the caloric intake be from fats and 1% from fatty acids. These figures are currently under revision (5.3). Variations and deficiencies in diet are not immediately dangerous. Even total deprivation will not seriously impair human abilities for six Earth-days at least. The exception is water: total deprivation will have serious effects in two Earth-days. V.2.5: Waste Recycling: Certain by-products of human existence require recycling or removal. As described in Section V.2.2, carbon dioxide must not accumulate in the environment. A human being produces between .39 and 9.82 grams of co 2 per minute depending on his/ her level of exercise (5.1). Solid wastes from humans, animals, and plants must also be recycled or removed from the human environment. Agricultural methods involving nitrogen-fixing methods produce harmful nitrites. Metabolic and food processing by-products which must be dealt with include hydrogen, carbon monoxide, hydrogen sulfide, ammonia, aldehydes, ketones, and hydrocarbons. Water for human consumption and plant growth must be cleared of harmful contaminants including salts (5.4). V.2.6: Light: The human eye is sensitive to light in a range of wavelengths between 380 and 780 millimicrons (1 millimicron = l09 m) (5.5). This sensitivity is shown in Figure 5.4.
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