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Nutrients

This is an excerpt from Nutrition for Sport, Exercise, and Health by Marie Spano,Laura Kruskall & D. Travis Thomas.

There are six groups of nutrients: carbohydrate, lipids, protein, vitamins, minerals, and water. Alcohol is not a nutrient, but it does contain energy (calories). Carbohydrates, fats (including fatty acids and cholesterol), protein (including amino acids), fiber, and water are macronutrients, which are required in the diet in larger amounts. Carbohydrates, fats, and proteins are also referred to as energy-yielding macronutrients becausethey supply the body with energy. Vitamins and minerals are micronutrients, which are required in the body in smaller amounts in comparison to macronutrients. A common misconception is that vitamins and minerals are energy nutrients. These do not contain energy, though they play essential roles in the production of energy. Deficiencies of certain vitamins and minerals can lead to fatigue. Macronutrients and micronutrients work together for optimal physiological function. The unit of energy in food is called a kilocalorie, commonly referred to as a calorie or kcal. A kilocalorie is the amount of heat it takes to raise the temperature of one kilogram of water by one degree Celsius. A person's energy requirements refer to the number of kilocalories needed each day. Food labels list calories per serving of the item. Both carbohydrate and protein contain 4 calories per gram, while lipidsprovide 9 calories per gram, making lipids more energy dense - that is, they contain more calories permass or volume than do carbohydrate or protein.

Nutrition Tip

Counting your carbs? Note that while all vegetables contain primarily carbohydrate, their content per serving is not the same. Vegetables can be categorized as starchy or nonstarchy. Starchy vegetables, such as potatoes, corn, and peas, contain approximately 15 grams of carbohydrate in a half-cup serving. Nonstarchy vegetables, such as broccoli, beets, and asparagus, contain considerably less carbohydrate - about 5 grams per half-cup serving. So if you want to reduce your intake of carbohydrate, choose nonstarchy vegetables.

Dietary Reference Intakes

The Institute of Medicine (IOM) of the United States Department of Agriculture (USDA) developed the Dietary Reference Intakes (DRIs), a set of recommendations based on the latest "scientific knowledge of the nutrient needs of healthy populations" (figure 1.1). The DRIs include:

• Estimated Average Requirement (EAR). The EAR is the estimated mean daily requirement for a nutrient as determined to meet the requirements of 50 percent of healthy people in each life stage and gender group (different amounts are provided based on age ranges and life stages, such as pregnancy and lactation). The EAR is based on the reduction of disease and other health parameters. It does not reflect the daily needs of individuals but is used to set the RDA and for research purposes.
• Recommended Dietary Allowance (RDA). The RDA is set to meet the needs of nearly all (97 - 98%) healthy people in each gender and life stage. This is the amount that should be consumed on a daily basis. The RDA is two standard deviations above the EAR based on variability in requirements, or if the standard deviation is not known, the RDA is 1.2 times the EAR.
• Adequate Intake (AI). The AI is the recommended average daily nutrient level assumed to be adequate for all healthy people. The AI is based on estimates - observed or experimentally determined approximations - and used when the RDA cannot be established because of insufficient data.
• Tolerable Upper Intake Level (UL). The UL is the highest average daily intake considered safe for almost all individuals. The UL represents average daily intake from all sources, including food, water, and supplements. Lack of a published UL does not indicate that high levels of the nutrient are safe. Instead, it means there isn't enough research available at this time to establish a UL.
• Acceptable Macronutrient Distribution Range (AMDR). The AMDR is a range given as a percentage of total calorie intake - including carbohydrate, protein, and fat - and is associated with a reduced risk of chronic disease and adequate intake of essential nutrients.
• Estimated Energy Requirement (EER). The EER is the average daily energy intake that should maintain energy balance in a healthy person. Factors such as gender, age, height, weight, and activity level are all considerations when calculating this value.

Figure 1.1 Dietary Reference Intakes. The AI or RDA describes the recommended daily amount of a nutrient, while the UL describes the amount not to exceed. Too little or too much of a nutrient can increase the risk of undesirable effects.

Energy-Yielding Macronutrients

The primary function of carbohydrate is to provide energy. Carbohydrate becomes increasingly important when exercising at a high intensity. High-intensity exercise increases energy (calorie) demands, and carbohydrate is a fast source of energy - the body can quickly access it - whereas fat, another source of energy, is much slower in meeting the body's demand for energy during high-intensity exercise. Carbohydrate can be stored, to an extent, in the human body as an energy reserve in the form of glycogen in the liver and muscle. The AMDR for carbohydrate is 45 to 65 percent of kilocalories for both males and females ages 19 and older. Common sources of carbohydrate are rice, pasta, wheat products, and grains such as corn, beans, legumes, fruits, vegetables, and milk. Some carbohydrates are considered nutrient-dense because they contain nutrients important for good health, including vitamins, minerals, and dietary fiber. A type of carbohydrate, fiber is discussed in detail in chapter 3.

Dietary fats and oils are examples of lipids. Dietary fats and oils provide energy and aid in the absorption of fat-soluble vitamins and food components. Fat can be stored in limitless quantities in the body, serving as an energy reserve. Fat can be an important energy source during long-duration activities, such as an ultra-endurance race. The AMDR for fat is 20 to 35 percent for both males and females ages 19 years and older. Common sources of fats include meat, nuts, seeds, oils, dairy products, and vegetable spreads.

Protein can be used for energy, but its primary function is to support cell and tissue growth, maintenance, and repair. Unlike carbohydrate and lipids, the primary purpose of protein is not to supply energy, so it is important to get an adequate amount on a regular basis. The RDA for protein is 56 grams per day for males aged 19 and over, and 46 grams per day for females aged 14 and over. The RDA for pregnant and lactating women of all ages is 71 grams per day. Despite these recommendations, considerable evidence suggests that the RDA for protein is too low to support muscle growth and maintenance, particularly for athletes and older adults. The AMDR for protein is 10 to 35 percent of calories for both males and females ages 19 and older. Common sources of protein include poultry, beef, fish, eggs, dairy foods, and some plant foods, particularly soy foods, nuts, and seeds.

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