72 Unit 2 Nutrition and Food Choices Copyright Goodheart-Willcox Co., Inc. You need to take in protein to replace what is lost every day. Fortu- nately, in the United States, many foods that people eat on a regular basis contain protein. If you’re like most Americans, you eat more protein than you need. Types of Proteins All proteins are made up of smaller chemical units called amino acids (Figure 3.3). Twenty different amino acids join in various combinations to make all types of protein. Some of these amino acids are produced in the body. These are called nonessential amino acids. Other types of amino acids are not produced by the body you can only get them by eating particular foods. This type of amino acid is called an essential amino acid because it is essential that your diet includes this type of nutrient. Protein sources are divided into two types, depending on whether or not they include all of the essential amino acids: • A complete protein source contains all nine of the essential amino acids. This type of protein is found in animal-based foods such as meat, poultry, eggs, fi sh, and dairy products (milk and cheese). fi • An incomplete protein source lacks one or more of the essential amino acids. This type of protein is found in legumes (dry beans and peas), tofu, nuts and seeds, grains, some vegetables, and some fruits. Protein’s Role in the Body Protein is required for the body to function properly. People who don’t consume enough protein risk serious consequences. For ex- ample, since immune cells are made of protein, individuals who have a protein defi are more likely to have weakened im- ficiency mune systems, which make it more likely for them to develop infections and diseases. Protein plays other important roles in the body, includ- ing acting as enzymes and hormones. H Hormones are chemi- cal messengers that infl many basic processes in your fluence body. Protein also serves as a transporter in the body and is involved in fl uid and pH balance. fl Protein and Vegetarians Because some vegetarians avoid eating all (or most) foods from ani- mal sources, they must rely on plant-based sources of protein to meet their protein needs. With some planning, a vegetarian diet can easily meet the recommended protein needs of adults and children. People who eat a veg- etarian diet need to take in different types of food that can work together to provide all of the essential amino acids. amino acid a small chemical unit that makes up proteins hormone a chemical substance in your body that influences fl many basic processes Steak is a complete protein, meaning it contains all nine essential amino acids. Do you consider complete protein foods like steak to be “healthy”? Why or why not? Figure 3.3