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In this chapter, we alluded to some of the major types of nutrients. The detailed structures of many of these were discussed in Chapter 2. We will now consider each in more detail with respect to the needs they fulfill in the body.
  • Carbohydrates: Carbohydrates are a group of molecules based on the monosaccharide, or simple sugar, subunit. We can consume them in complex form as polysaccharides like starch, or in simple forms, as mono- or disaccharide sugars. Carbohydrates are prevalent in plant tissues such as fruits and grains, and function mainly to provide the body with energy.
  • Proteins:  Proteins are polymers of amino acids. They are abundant in animal foods like meat, and are necessary largely to supply amino acid building blocks for the construction of the body’s own proteins. Since they can be converted to glucose or fat, they can also provide energy in times of need. Eight amino acids must be ingested and are referred to as essential, but the body can synthesize the other needed twelve. A complete protein source contains all twenty of the necessary amino acids.
  • Fats: Fats are lipids composed of one molecule of glycerol attached to three fatty acid chains. They are often abundant in animal products, and play several roles in the body, including their primary function in long-term energy storage. Fats are also important in the synthesis of cell membranes and certain hormones. The body needs but cannot manufacture certain polyunsaturated fatty acids, which therefore must be consumed and are referred to as essential fatty acids.
  • Vitamins: Vitamins are essential organic compounds that the body cannot synthesize but needs for a wide variety of purposes. Many act as coenzymes in metabolic pathways, and are usually required in relatively small amounts. Others act as antioxidants, protecting important molecules from oxidation and damage by free radicals and thus potentially playing a role in the prevention of cancer. Vitamins are often classified according to their solubility properties; A, D, E, and K are fat soluble, while the many vitamins in the B complex and C dissolve readily in water. The required vitamins can usually be obtained from a variety of plant and animal sources, although supplementation is a common practice, especially if the diet is deficient.
  • Minerals: Like vitamins, minerals are essential substances the body must obtain from the environment and are used for a variety of functions. Unlike vitamins, however, minerals are inorganic, usually elemental, substances that are often ingested as ionic salts; thus they dissociate in water and are often referred to as electrolytes. Examples of important minerals are calcium, phosphorus, sodium, potassium, chloride, and iodine. As with vitamins, these can usually be obtained in sufficient quantities from a normal diet, but are sometimes supplemented due to other factors.
  • Water: No discussion of nutrition would be complete without a mention of water, probably the most essential nutrient. While we likely take it for granted, water is vital in many ways to the functioning of the body. As the major solvent present in our cells, it accounts for much of the mass of the entire organism, and is especially important as a part of the blood and lymph. Dehydration, if severe enough, will inevitably lead to death. While the body can “manufacture” a certain amount of water as it engages in metabolic reactions, water must be ingested to ensure an adequate supply.

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