Levetin−McMahon: Plants and Society, Fifth EditionIII. Plants As a Source of Food10. Human Nutrition © The McGraw−Hill Companies, 2008156UNIT IIICHAPTER OUTLINE Macronutrients 157Sugars and Complex Carbohydrates 157 A CLOSER LOOK 10.1 Famineor Feast 158Fiber in the Diet 160 Proteins and Essential Amino Acids 160 Fats and Cholesterol 161 Micronutrients 164Vitamins 164 Minerals 169 Dietary Guidelines 170Balancing Nutritional Requirements 171 A Healthier Food Pyramid 172 A CLOSER LOOK 10.2 Eat Broccoli for Cancer Prevention 174Meatless Alternatives 175 Chapter Summary 175 Review Questions 176 Further Reading 176 KEY CONCEPTS 1. Human nutritional needs are supplied by macronutrients (carbohydrates, proteins, and fats) and micronutrients (vitamins and minerals). 2. If nutritional requirements are not satisfied, deficiency diseases can result that have widespread effects in the bodily systems. 3. Plants can supply the majority of human nutritional requirements, and there is evidence that increasing the proportion of plant foods in the diet can have positive health benefits. 10Human Nutrition The amount of trans fats per serving is listed on the Nutrition Facts label to allowconsumers to monitor and hopefully limit a nutrient implicated in increasingthe risk of cardiovascular disease CHAPTERLevetin−McMahon: Plants and Society, Fifth EditionIII. Plants As a Source of Food10. Human Nutrition © The McGraw−Hill Companies, 2008CHAPTER 10Human Nutrition 157 New ideas in nutrition are quickly incorporated by the health-conscious segment of society and advertisers looking for a new marketing gimmick. The benefits of several nutritional concepts such as fiber, monounsaturated oils, and low-carbohydrate diets have made headlines and influenced lifestyle changes. All these concepts promise bet-ter health and are, in fact, dependent on a greater consumption of plants in the human diet. This chapter will examine human nutritional needs and how plants can satisfy these needs. MACRONUTRIENTSThe basic nutritional needs of humans are to supply energy and raw materials for all the various activities and processes that occur in the body. In addition to the need for water, humans require five types of nutrients from their food supply; three of these are required in relatively large amounts and are called macronutrients, consisting of carbohydrates, pro-teins, and fats. The other two types of nutrients, vitamins andminerals, are required in small amounts and are known as micronutrients. If water were removed, the macronutrients would make up almost all the dry weight of foods. * Human energy requirements vary with the age, sex, and activity level of the individual, within a wide range of 1,200 to 3,200 kilocalories per day. The current reccommendation for Americans is an average daily intake of 2,000 kilocalories or 1,600 kilocalories for women and 2,200 kilocalories for men. (A calorie is a measure of energy—technically, the amount of energy needed to raise the temperature of one gram of water one degree Celsius.) Food energy is normally measured in kilocalories (1,000 calories ⫽ 1 kilocalorie), which can be abbreviated as kcal o r Calories with a capital C. Most dietary guides simply use the term calories, but this book will use the more accurate Calories or kilocalories. Each gram of carbohy-drate or protein can supply 4 kilocalories while, for each gram of fat consumed, the amount of energy supplied is more than double, 9 kilocalories. Although all the macronutrients can be used as a source of energy, normally only carbohydrates and fats do so while proteins provide the raw materials, or build-ing blocks, required for the synthesis of essential metabolites, growth, and tissue maintenance. The consequences of under-nutrition, malnutrition, and overnutrition for the world’s popu-lation are the topics of A Closer Look 10.1—Famine or Feast. Sugars and Complex Carbohydrates Although carbohydrates are commonly grouped into sugars and starches, recall (see Chapter 1) that these compounds can be chemically classified into monosaccharides, disaccha-rides, and polysaccharides, based on the number of sugar units in the molecule. *All organisms have nutrient needs requiring some compounds in large amounts (mac-ronutrients) and other compounds in smaller amounts (micronutrients). In Chapter 1, we discussed the elements that plants require and used the terms macronutrients andmicronutrients to refer to the mineral requirements. When referring to human nutri-tional needs, these terms take on a different meaning, as discussed here. MonosaccharidesMonosaccharides are the basic building block of all carbohy-drates, and glucose is the most abundant of these sugars. During the process of digestion, many carbohydrates are broken down or converted into glucose, which is then transported by the blood to all the cells in the body. Within cells, the process of cellular respiration metabolizes glucose to produce the energy necessary to sustain life. Other common monosaccharides are fructose and galactose, which have the same chemical makeup as glucose, C 6H12O6, differing only in the arrangement of the atoms within the molecules. In the body, most fructose and galactose are converted into glucose and metabolized as such. In the United States, an inexpensive sweetener for many types of processed foods is high-fructose corn syrup, often preferred because fructose is sweeter tasting than table sugar. Fructose is commonly found in many fruits, unlike galactose, which does not normally occur free in nature. DisaccharidesDisaccharides are composed of two monosaccharides chemi-cally joined together. The most common disaccharide is sucrose, or table sugar, formed from a molecule of glucose and a molecule of fructose. Other disaccharides are the milk sugar lactose (a combination of glucose and galactose) and maltose (formed by two glucose molecules), which is largely found in germinating grains. Table sugar, which primarily comes from sugarcane and sugar beet, is at least 97% pure sucrose with little nutritional value, thereby supplying only calories. (See A Closer Look 4.2—Sugar and Slavery.) During digestion, these disaccharides are broken down to yield their component monosaccharides. PolysaccharidesPolysaccharides, also known as complex carbohydrates, contain hundreds to thousands of individual sugar units, and for the most part, glucose is the only