For body builders and increasingly, for endurance athletes, protein-rich foods are as necessary as the air they breathe.

For these athletes, protein is a must because it builds and maintains muscle. Protein also replenishes the amino acid supply that produces enzymes, hormones and other tissues they need to compete. They know that eating high-quality protein (meat, fish, eggs, dairy or soy) within two hours after exercise -- either by itself or with a carbohydrate -- enhances muscle repair and growth.

But for the rest of us non-extreme and everyday human beings, protein remains an essential nutrient for our bodies that we have to replenish daily. Needless to say, proteins do most of the work in our cells and are required for the structure, function and regulation of the body’s tissues and organs.

So, how much protein do we need to keep functioning?

A review of medical literature about proteins affirms that protein should be consumed on a regular basis. The doctors involved in the review recommend that we choose unprocessed meat, poultry, seafood, eggs or dairy as protein sources.

Consuming animal products helps ensure we receive all the essential amino acids our bodies need. We need to remember, however, that only a limited amount of protein can be absorbed by our bodies during a meal.

If you eat more protein than your body can absorb, the excess amino acids might be used for gluconeogenesis, which produces glucose. Protein might also increase insulin levels when consumed in large amounts. Its effect on insulin may vary significantly from person to person, however.

In the review, doctors recommend eating a low-carbohydrate, high-fat diet with moderate protein. This applies to all levels of carb restriction.

They defined “moderate” protein as some 1.2 grams to 1.7 grams per kilogram of ideal body weight per day for adults. The doctors said protein intake within this range “has been shown to preserve muscle mass, improve body composition, and provide other health benefits in people who eat low-carb diets or higher-carb diets.”

They said that while this recommendation is at least 50 percent higher than the minimum Recommended Daily Allowance (RDA) for protein of 0.8 g/kg of body weight, it is less than “high-protein” diets containing more than 2 g/kg of protein per day.

They said this amount is only beneficial when needs are truly increased, such as healing from major injury or surgery.