NUTRITIONAL REQUIREMENTS: COMPONENTS OF A HEALTHY DIET
You probably think about your diet in terms of the foods you like to eat. More important for your health, though, are the nutrients contained in those foods. Your body requires proteins, fats, carbohydrates, vitamins, minerals, and water about 45 essential nutrients. In this context, the word essential means that you must get these substances from food because your body is unable to manufacture them, or at least not fast enough or in sufficient amounts to meet your physiological needs. The six classes of nutrients, along with their functions and major sources, are listed in Table 8.1
NUTRITIONAL REQUIREMENTS: COMPONENTS OF A HEALTHY DIET Photo Gallery
The body needs some essential nutrients in relatively large amounts; these macronutrients include protein, fat, carbohydrate, and water. Micronutrients, such as vitamins and minerals, are required in much smaller amounts. Your body obtains nutrients through the process of digestion, which breaks down food into compounds that the gastrointestinal tract can absorb and the body can use (Figure 8.1). A diet that provides enough essential nutrients is vital because they provide energy, help build and maintain body tissues, and help regulate body functions.
Food is partially broken down by being chewed and mixed with saliva in the mouth. After traveling to the stomach via the esophagus, food is broken down further by stomach acids and other secretions. As food moves through the digestive tract, it is mixed by muscular contractions and broken down by chemicals. Most absorption of nutrients occurs in the small intestine, aided by secretions from the pancreas, gallbladder, and intestinal lining. The large intestine reabsorbs excess water; the remaining solid wastes are collected in the rectum and excreted through the anus.
