Protein Explained

Protein is an important dietary macronutrient that can be found in each bodily cell.  Because the body stores protein differently than it does carbohydrates and fats, daily consumption of protein is necessary for optimal health and functioning.

How Much Protein Is Needed on a Daily Basis?

In countries where most people do not have regular access to protein sources, a deficiency called kwashiorkor can develop.  However, most people who live in developed countries get more than an adequate amount of protein in their diet. Vegans and vegetarians usually have no trouble acquiring enough protein as long as they are aware of what they eat.  An average, healthy adult should be consuming between 45 and 60 grams of protein daily.  This requirement can change based on a variety of factors.  Pregnant women, for example, should try to ensure that they eat a daily average of 70 grams of protein as their fetus develops.  The Centers for Disease Control and Prevention (CDC) offers the following Recommended Dietary Allowances for Protein based on age:

  • 1 to 3 years: 13 g
  • 4 to 8 years: 19 g
  • 9 to 13 years: 34 g
  • 14 to 18 years (females): 46 g
  • 14 to 18 years (males): 52 g
  • Adult females: 46 g
  • Adult males: 56 g

What Foods Are Good Sources of Protein?

Meats and seafood are often very high in protein; 3 ounces of salmon offer about 23 grams.  Many animal products are also good sources.  For example, one egg contains 6 grams of protein and a cup of skim milk has 8 grams.  A half a cup of cottage cheese contains 14 grams.  Vegetarians will want to emphasize tofu (20 g per half cup), and various types of beans (15g, 13g, and 12g per cup for black, kidney, and garbanzo beans, respectively).  Keep in mind that not all sources of protein are necessarily healthy.  For example, although red meats usually contain ample protein, they are also notoriously high in saturated fat, which is known to increase blood levels of bad cholesterol. 

What Does Protein Do for the Body?
The protein in the body is part of a cyclical process that breaks it down, uses it to build up the body, and then replaces the stores that will only be broken down again.  When we eat foods that contain protein, digestion converts the protein into a usable form called amino acids.  These are the “replacements” for the protein that our body has used. Protein is found in hair, bone, skin, muscle – everywhere.  Also, the enzymes responsible for numerous chemical reactions are constructed from amino acids.

There is not nearly as much research on how protein consumption influences health as there is on the effects of consuming fats and carbohydrates. Scholars, however, recognize the relationship between proteins and extreme immune response, more commonly understood as allergies. Additionally, the digestion of protein produces acids that are neutralized by various agents including calcium.  Inconclusive evidence suggests that this use of calcium over a prolonged period could increase risk for osteoporosis and/or bone fractures.

With so many popular diets (like the Atkins and South Beach diets) emphasizing high protein consumption to reduce hunger and control weight, there has been concern about the effects of eating excessive fat (often in the red meats that these diets encourage) and the corresponding risk of heart disease.  Protein has also historically been used among bodybuilders and athletes, often in the form of high-protein shakes.  However, unless you have specific goals that you have discussed with your doctor, the best policy for any component of your diet is moderation.

Are There Different Types of Protein?
“Protein” is really a general term to describe many possible combinations of the 20 amino acids.  The body can make some amino acids but others must be acquired from food sources.  The latter type (the ones we can’t make) are called essential amino acids.  Foods are generally considered to fall into one of two categories: complete protein sources or incomplete protein sources.  Complete sources give us all of the essential amino acids and include eggs, poultry, cheese, milk, and meat.  Incomplete sources are low in certain essential amino acids.  Two incomplete protein sources are considered to be complementary if, when eaten together, they can fulfill a person’s requirements for all of the essential amino acids.  Although previous beliefs held that complementary proteins (e.g., rice and beans) needed to be consumed in the same meal, current research indicates that it is only necessary to consume them on the same day.