Nutrition is the science that deals with food and how the body uses it. All living things need food to live. The food supplies energy, which people need to perform certain actions. Food also provides substances that the body needs to build and repair its tissues and to regulate its organs and organ systems.
Food provides certain chemical substances needed in order for a person to maintain good health. These chemical substances are called nutrients. Nutrients can perform three important functions. They provide materials for building, repairing, or maintaining body tissues. They help regulate body processes. They serve as fuel to provide energy. The body needs energy to maintain all its functions. People who do not get enough nutrients are sometimes lazy and are unwilling to work.
The foods we eat contain thousands of different chemicals. Our body, however, only needs only a few dozen of these chemicals in order to stay healthy. These are the nutrients that the body needs. Nutrients are divided into six main groups. They are (1)water, (2)carbohydrates, (3)fats, (4)proteins, (5)minerals, (6)vitamins. Water, carbohydrates, fats, and proteins are called macronutrients. Since macro means large, the body needs these four nutrients in large amounts. Minerals and vitamins are called micronutrients (because micro means small). The body needs only small amounts of these nutrients.
Water is the most important nutrient. Our bodies can survive without other nutrients for several weeks, but we can only go without water for about one week. Water is needed in great amounts because the body consists largely of water. Between 50 and 75 percent of a normal person's body weight is made up of water. The body needs water to carry out all of its life processes. Watery solutions help dissolve other nutrients and carry them to all of the tissues. The body also needs water to carry away waste products and to cool itself. Adults should drink about 2 1/2 quarts of water every day.
The carbohydrates, fats, and proteins are needed because they have nutrients which provide energy.
Carbohydrates include all sugars and starches. They are the main source of energy for living things. There are two types of carbohydrates, simple and complex. Simple carbohydrates include sugars and have a simple molecular structure. Complex carbohydrates include starches and have a larger and more complicated molecular structure. The structure consists of many simple carbohydrates linked together.
Fats are a highly concentrated source of energy. All fats are composed of an alcohol called glycerol and substances called fatty acids. A fatty acid consists of a long chain of carbon atoms. There are three types of fatty acids. They are saturated, monounsaturated, and polysaturated. This is a chart that describes the amount of fat per serving. The bold words can be found on many food products in the supermarket.
Fat free: less than 0.5 grams of fat per serving
Saturated fat free: less than 0.5 grams of saturated fat per serving, and the level of trans fatty acids does not exceed 1% of total fat
Low fat: 3 gram or less per serving and, if the serving is 30 grams or less or 2 tablespoons or less, per 50 grams of the food
Low saturated fat: 1 grams or less per serving and not more than 15% of calories from saturated fatty acids
Reduced or Less fat: at least 25% less per serving than compared food
Proteins serve as one of the main building materials for the body. Skin, cartilage, muscle, and hair are made up largely of proteins. Protein also contains enzymes which speed up chemical reactions. Cells could not function without these enzymes. Proteins also serve as hormones (chemical messengers) and as antibodies (disease fighting chemicals). Proteins are large, complex molecules made up of smaller units called amino acids. The body must have a sufficient supply of twenty amino acids. It can produce eleven of them in sufficient amounts. The nine others are called essential amino acids. The body cannot make these amino acids. They must come from food. The best sources of protein are cheese, eggs, lean meat, fish, and milk. The proteins in these foods are called complete proteins. They are called this because they contain adequate amounts of all the essential amino acids. Cereal grains, legumes (plants of the pea family), vegetables, and nuts also supply proteins to the body. These proteins are