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.
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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
- Eggs
- Tofu
- 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
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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.
When we don’t have enough protein, we may experience:
- Loss of muscle mass that can cause physical weakness
- Fatigue
- A weakened immune system
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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 - 70+
|
46
|
|
Men ages 19 - 70+
|
56
|
However, most American adults often exceed the recommended intake. Actual protein
consumption for American adults ranges from 88 to 92 grams for men and 62 to 66
grams for women, or about 1.04 to 1.25 grams of protein per kilogram of body weight
per day.
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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.
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Summary
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.