Protein is one powerful nutrient. It is part of every living cell, and it plays a major role in your body — from building your body tissues to making important hormones. An adequate protein intake in the diet is important across the life cycle, especially as we age. Keep reading to learn more about protein, including:
What Is Protein?
Protein is an important macronutrient used by the body for building, repairing and maintaining tissues. Proteins are part of every cell, tissue, and organ in our bodies. Proteins are made up of amino acids, which are the building blocks of protein. There are 20 different amino acids needed by the body. These amino acids join together to make all different types of protein. Eight amino acids are considered essential amino acids since they not made by the body and therefore must be obtained from food. The other 12 amino acids are made by the body and are considered nonessential amino acids.
The proteins in our bodies are constantly being broken down and replaced. The body does not store amino acids like it does carbohydrates and fats, so the body needs a daily supply of amino acids to make new proteins. The protein in the foods we eat is digested into amino acids that can be used to replace the proteins in our bodies.
What Are the Different Types of Protein in the Diet?
There are different types of protein in our diet — complete and incomplete proteins. The "completeness" (or quality) of a protein is determined by its amino acid composition. A complete protein source is one that provides all of the essential amino acids. Complete proteins come from animal sources (e.g. eggs, milk, meat, poultry, and fish) and foods made from soy (e.g. tofu and tempeh). About 75% of the protein we eat in our diets should be complete or high-quality protein. An incomplete protein source is one that is low in one or more of the essential amino acids. Most plant proteins (e.g. legumes and nuts) are incomplete proteins because they do not contain all the essential amino acids. Incomplete proteins can be combined (e.g. beans and rice, milk, and cereal) to obtain protein of sufficient quality to be considered complete.
Typically, good sources of protein include:
- Meats, poultry, and fish
- Milk and dairy products
- Legumes (dry beans and peas)
Here are examples of amounts of protein in various foods:
- 3-ounce piece of meat contains about 21 grams of protein
- 1 cup of milk contains about 8 grams of protein
- 1 cup of dry beans contains about 16 grams of protein
The Role of Protein in the Body
As a nutrient, protein performs many functions in the body. An adequate dietary protein intake is important for building, maintaining and repairing body tissues. The body’s structural components, such as skin, muscles, bones, and organs, are made up in large part by protein. Many hormones and enzymes that function to regulate body processes and chemical reactions are made of protein. Protein is also used to make antibodies to fight disease. If you do not consume enough carbohydrate and fat, proteins can also supply your body with energy.
Current Protein Intake Recommendations
The Food and Nutrition Board of the Institute of Medicine recommends that healthy adults get a minimum of 0.8 grams of protein for every kilogram of body weight per day. This is equal to about 8 grams of protein for every 20 pounds of body weight. A protein intake at this level will help to keep the body from slowly breaking down other own tissues. See the chart below for the amount of protein in grams per day for adult men and women.
Recommended Dietary Allowance (RDA) for Protein
||Grams of protein needed each day
|Women ages 19 to 70+
|Men ages 19 to 70+
Protein Needs for Older Adults
Current research and expert opinion, however, shows that the RDA for protein of 0.8 grams per kilogram of body weight may not be adequate as we age. The current RDA was made based on research in young adults and does not promote optimal health or protect older adults from sarcopenic muscle loss (loss of muscle and function with aging). Experts now estimate that older adults need 1.2 grams of protein per kilogram of body weight or higher per day. Additionally, researchers recommend that an adequate amount of protein intake with each meal is important to promote protein anabolism (or protein building). These recommendations state that an intake of 25 to 30 grams of high-quality protein per meal is necessary for optimal muscle protein synthesis. Protein intakes at this level are particularly beneficial for older adults as a strategy to maintain muscle mass.
Protein has many important roles in our bodies and is part of every tissue, including our organs, muscles, and skin. We need to make sure we eat enough high-quality protein in our diets, especially as we age so that our bodies have the amino acids it needs to function properly. New research is showing that older adults may need more protein than current recommendations to help optimize their health and protect their lean muscle mass.