Six Major Nutrient Groups
The body uses nutrients for growth, maintenance, and repair and needs to take in about 40 varieties to function properly. Nutrients can be grouped into six categories: carbohydrate, protein, lipid (fat), water, vitamins, and minerals (see table 8.1).
These six nutrients are further classified according to size and energy. Carbohydrate, protein, and fat are macronutrients because they make up the bulk of your diet. Vitamins and minerals are micronutrients because they are required in much smaller amounts. For example, the average person consumes about 2.5 gallons (9.5 L) of food and water per day, but only an eighth of a teaspoon of that is vitamins and minerals. This does not mean that vitamins and minerals are unimportant. The ignition key is only a small part of a car, but it’s hard to get the car started without it! A deficiency in B12, just one of the eight B vitamins, can result in anemia, hypersensitive skin, and degeneration of peripheral nerves resulting in paralysis (Whitney & Rolfes, 2012). You may have noticed the omission of water as a macronutrient. People definitely need a large supply of water; however, water is a micronutrient because it does not contain energy.
Food energy is measured in calories. You may recall from high school chemistry that a calorie is the amount of energy necessary to raise the temperature of one kilogram of water by one degree Celsius. When discussing nutrition and exercise, however, calorie usually means kilocalorie, 1,000 calories, or the amount of energy necessary to raise the temperature of 1 liter of water by 1 degree Celsius. To avoid confusion, when calorie is used in this text it will be used in the conventional manner.
The energy nutrients are carbohydrate, protein, and fat; the nonenergy nutrients are water, vitamins, and minerals.
Carbohydrate is fuel for the body and brain and comes in three types: simple carbohydrate, complex carbohydrate, and fiber. Simple carbohydrate is further divisible into monosaccharides, which contain only one type of sugar—such as glucose (blood sugar), fructose (fruit sugar), and galactose (milk sugar)—and disaccharides, which are made up of glucose combined with another sugar. The three primary disaccharides are maltose, lactose, and sucrose; what most people mean by sugar. Complex carbohydrate, or starch, is a polysaccharide, which contains long chains of glucose molecules bonded together. Because the body must break these bonds to release the chemical energy stored in them, complex carbohydrate takes longer to digest and therefore allows for a more sustained energy release than simple carbohydrate does. In some cases these bonds cannot be broken down by human digestion, as is the case with fiber.
Unlike animals, humans lack the necessary enzymes to break down the energy in fiber. Fiber comes in two types: soluble and insoluble. Soluble fiberdissolves in water to form a gel, and it can help lower blood cholesterol and control blood sugar levels. Insoluble fiber does not dissolve, and it can help prevent constipation and other bowel disorders. Each of the three types of carbohydrate and their subcategories and primary functions are listed in table 8.2.
The 2010 dietary guidelines published by the U.S. Department of Health and Human Services (HHS) and the U.S. Department of Agriculture (USDA) recommend that 45 to 65 percent of total calorie intake come from carbohydrate—at least 130 grams of carbohydrate per day (U.S. Department of Agriculture and U.S. Department of Health and Human Services, 2010). This minimum is required to supply the brain with an adequate amount of glucose. It is a fairly moderate recommendation, considering that the average American adult male consumes 220 to 330 grams and the average American adult female consumes 180 to 230 grams of carbohydrate daily (Institute of Medicine, 2002). According to the Institute of Medicine (2002), an agency that works with HHS and the USDA to establish nutritional guidelines, an adequate intake of fiber is 14 grams for every 1,000 calories.