and our level of physical activity has a major impact on how we use the nutrients in our food.We can perform more strenuous activities for longer periods of time when we eat a nutritious diet, whereas an inadequate or excessive food intake can make us lethargic. A poordiet, inadequate or excessive physical activity, or a combination of these also can lead to serious health problems. Finally, several studies have suggested that healthful nutrition and regular physical activity can increase feelings of well-being and reduce feelings of anxiety and depression. In other words, wholesome food and physical activity just plain feel good!What Are Nutrients?We enjoy eating food because of its taste, smell, and the pleasure and comfort it gives us. However, we rarely stop to think about what our food actually contains. Foods are composed of many chemical substances, some of which are not useful to the body, and others of which are critical to human growth and function. These latter chemicals are referred to asnutrients. • carbohydrates• lipids (including fats and oils)• proteins• vitamins• minerals• waterAs you may know, the term organic is commonly used to describe foods that are grown with little or no use of chemicals. But when scientists describe individual nutrients as organic, they mean that these nutrients contain an element called carbon that is an essential component of all living organisms. Carbohydrates, lipids, proteins, and vitamins are organic,because they contain carbon.Minerals and water are inorganic because they do not contain carbon. Both organic and inorganic nutrients are equally important for sustaining life but differ in their structures, functions, and basic chemistry. You will learn more about the details of these nutrients in subsequent chapters; a brief review is provided here.
Carbohydrates,Lipids,and Proteins Provide Energy
Carbohydrates, lipids, and proteins are the only nutrients in foods that provide energy. By this we mean that these nutrients break down and reassemble into a fuel that the body uses to support physical activity and basic physiologic functioning. Although taking a multivitamin and a glass of water might be beneficial in some ways, it will not provide you with the energy you need to do your 20 minutes on the stair-climber! The energy nutrients are also referred to as macronutrients. Macro means “large,” and thus macronutrients are those nutrients needed in relatively large amounts to support normal function and health. Alcohol is found in certain beverages and foods, and it provides energy—but it is not considered a nutrient. This is because it does not support the regulation of body functions or the building or repairing of tissues. In fact, alcohol is considered to be both a drug and a toxin. Details about alcohol are provided in the In Depth look on pages 154–165. We express energy in units of kilocalories (kcal). Refer to the Highlight box “What Is a Kilocalorie?” for a definition of this term. Both carbohydrates and proteins provide 4 kcal per gram, alcohol provides 7 kcal per gram, and lipids provide 9 kcal per gram. Thus, for every gram of lipids we consume, we obtain more than twice the energy as compared with a gram of carbohydrate or protein. Refer to the You Do the Math box on page 12 to learn how to calculate the energy contribution of carbohydrates, lipids, and proteins in one day’s diet.
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