Food And Evolution: Toward a Theory of Human Food Habits

9. Biocultural Consequences of Animals Versus Plants as Sources of Fats, Proteins, and Other Nutrients

LESLIE SUE LIEBERMAN Biocultural Consequences of Animals Versus Plants as Sources of Fats, Proteins, and Other Nutrients THIS CHAPTER DESCRIBES THE PHYSIOLOGICAL AND SOCIOcultural consequences of widely divergent diets based on either high animal or high plant intake. I examine variability in nutrient needs and nutrient sources and the benefits and liabilities of deriving nutrients from either animals or plants, using an evolutionary-adaptational framework to discuss population variability and the biochemical consequences of over- or under-consumption of protein , fats, and other nutrients. Human Nutrient Needs The long-established broad classification of the functions of nutrients in the body is still valid. Nutrients function (1) to supply energy; (2) to promote the growth and repair of body tissues; and (3) to regulate body processes. The nutrients that perform these functions are divided into five main categories: carbohydrates, lipids, proteins, minerals, and vitamins. A classification of the essential nutrients in each of these broad groupings is presented in Figure 9.1 (Guthrie 1975). There is one essential carbohydrate: glucose; one essential lipid: linoleic acid; nine essential amino acids; 15 essential minerals; and 13 essential vitamins. In addition, both water and fiber are needed. Sources of energy are provided by carbohydrates, lipids, and proteins, but minerals and vitamins are also necessary to catalyze the use of these nutrients. The nutrients that humans need have been well established. However, the quantities needed of these different nutrients have been under revision for a number of years and are still an area of controversy. The estimates of nutrient 225 III. Nutritional and Biopsychological Constraints FIGURE 9.1. Essential Nutrients for Humans Water Fiber Carbohydrate Glucose Fat or Lipid Linoleic acid Protein (Amino Acids) Histidine Isoleucine Leucine Lysine Methionine Minerals Calcium Chlorine Chromium Copper Fluorine Iodine Iron Magnesium VitamIns FAT-SOLUBLE A o WATEI~-SOLUBLE Ascorbic acid (C) Biotin Folacin Niacin Panthothenic acid SOURCE: Guthrie (1975: 10-11). 226 Phenylalanine Threonine Tryptophan Valine Manganese Molybdenum Phosphorus Potassium Selenium Sodium Zinc E K Pyridoxine (B(-») Riboflavin (BL ) Thiamine (Bl ) Vitamin (BIL) 9. Biocultural Consequences of Animals Versus Plants requirements are determined by a number of techniques: (1) collection of data on nutrient intake from the food supply of normal, healthy people; (2) review of epidemiological observations when clinical consequences of nutrient deficiencies are found; (3) biochemical measurements that assess degree of tissue saturation and molecular function; (4) nutrient balance studies that measure nutritional status; (5) studies of subjects maintained on diets containing marginally low or deficient levels of nutrients followed by corrective measures; and (6) extrapolation from animal experiments in which deficiencies are not corrected. The results of these studies indicate that there is tremendous individual and population variability in all the biochemical processes involved in processing food. The biologist Rene Dubos has stated that "every person has a nutritionalmetabolic pattern that is characteristic, indeed as unique as a fingerprint" (1980: 14). One classic study of inter-population differences evaluated the protein requirements of American Caucasian males and Taiwanese Oriental males. Urinary nitrogen loss was significantly greater among the American students (Scrimshaw and Young 1978). In other studies comparing individuals, protein utilization differences of over 100 percent were observed for some essential amino acids. The reasons for variation in protein needs might include the following : (1) differences in absorption capacity; (2) differences in urinary nitrogen excretory rates; (3) differences in hormonal response to anxiety or stress; (4) differences in sweat loss during physical acdtvity; (5) differences in energy or carbohydrate intake and need; and (6) unknown genetic and environmental variables (Scrimshaw and Young 1978). (See Chapter 6 for further discussion of biochemical variation.) Because of these and other experimental findings, in the early 1970s the commissions on nutrition of the World Health Organization and the Food and Agricultural Organization scaled down the protein requirements of healthy persons some 30 percent (FAO 1973). As Dubos (1980) points out, this eliminated , by administrative decision, the international "protein gap" that had been postulated in earlier decades. It did not, however, eliminate the controversy over protein needs. The Quantification of Nutrients (Recommended Dietary Intakes) A brief discussion of the U.S. recommended dietary allowances (RDAs) for proteins and amino acids will serve to illustrate the points of controversy concerning the establishment of appropriate nutrient intake levels. The RDAs prescribe daily amounts of essential nutrients for population groups described 227 III. Nutritional and Biopsychological Constraints by age, sex, weight, and physiological state (i. e., whether pregnant or lactating or...