Proteins provide the structure to all the cells and tissues in your body. The body constantly breaks down protein and uses new proteins to recreate the structure of your cells. Protein also helps transport nutrients across cell membranes and keeps your immune system healthy. Thousands of proteins exist, but they are not equal in value.
Amino Acids
Proteins are made up of several substances called amino acids linked together. The type of protein created depends on the order in which the amino acids combine. There are a total of 22 amino acids. Your body can synthesize 13 of them, so they are referred to as nonessential. The remaining 9 amino acids cannot be synthesized in your body. These are called essential amino acids. The term "essential" means you must consume them in your diet.
Types of Protein
Proteins are divided into two classes, based on their amino acid structure. Complete proteins are those that contain all 9 essential amino acids. Complete proteins are often referred to as high-quality proteins. Most complete proteins are animal sources, such as meat, poultry, eggs, milk, cheese and fish. Incomplete proteins are those that are missing one or more essential amino acid. Most vegetable protein sources, such as beans, nuts and rice, are incomplete proteins.
Protein Scoring
Proteins are also given a score based on their amino acid profile and how easily the body can digest them. This score, which is referred to as protein digestibility corrected amino acid score, or PDCAAS, rates proteins on a scale of 0 to 100 percent. Milk, which is easily digested and contains all the essential amino acids, is rated 100 percent.
Protein Needs
There are two ways to calculate your protein needs. The first method is by using a reference intake called the acceptable macronutrient distribution range, or AMDR. This range provides protein recommendations based on the number of calories you consume. Protein should comprise 10 to 35 percent of your daily calorie intake. If you are on a 2,000-calorie per day diet, your protein intake should be 50 g to 175 g.
A more precise way to calculate protein needs is by your body weight. Adults should consume 0.8 g of protein for every kg of body weight. For a 150-pound adult, this would equal approximately 55 g of protein.
Choosing Protein
When choosing protein, an easy way to make sure you get all the essential amino acids is to choose complete, or high-quality, proteins. Some complete proteins can be high in fat, however. Most of your complete proteins should be lean cuts of meat, fish or low-fat dairy products.
Since vegetarians do not consume animal proteins, getting sufficient amounts of protein can take some planning. It is important for vegetarians to eat vegetable proteins that complement each other. Complementary proteins contain different structures and in combination provide all the essential amino acids. Rice and beans are a good example of complementary proteins. Rice contains various essential amino acids that beans do not, and vice versa. Eating rice and beans together can provide you with all of the amino acids. You could also make oatmeal with milk to ensure that you are getting all the essential amino acids.
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