We all need to consume some amount of protein on a regular basis, but just how much can vary according to a person’s lifestyle and athletic focus.

Why is there a continual need for protein in the diet?

It is necessary to have a certain level of protein in the diet on a constant basis. This is because proteins, unlike other macronutrients, are “turned over” in the body. This means that the body needs incoming protein for synthesis to compensate for the amount lost through degradation. When this occurs in equilibrium, the system is said to be in “nitrogen balance”. The state of the body due to growth, aging, activity level, pregnancy, and diet is called the protein or nitrogen balance (the term derives from the measurement of nitrogen in various tests, and refers to the amount of protein that is gained or lost across a given period).

Protein is used more as contributor to the structural and functional elements of the body than as fuel, although the body does look to protein as an energy source in some situations. When in a fasted state, for instance, the body will rely on stored fuel sources. And because the body needs a constant source of protein, if need be, it will resort to muscle tissue because that is where protein is stored. The term for the body breaking down a given material for use as fuel (or for another purpose) is catabolism.

Turnover in muscle is actually small in relation to the mass of the muscle — only about 25-35% of total protein turnover comes from muscle tissue. Within the muscle exists an amino acid pool that is tapped into first for synthesis; protein from muscle will then be tapped into in order to replenish any losses from that pool.

Are protein needs different in different people?

The amount of protein needed by athletes and sedentary people are different, however. Just how different or how much is needed for normal performance remains a debated point. In some clinical situations, morbidly obese patients may be put on a “protein sparing, modified fast” (PSMF) diet, which has very few calories but a sufficient amount of protein to compensate for losses.

An athlete’s protein needs are determined by his or her training regime and customary intake of nutrients. But it has been shown that athletes require more protein than sedentary people because more protein is used for fuel and more is being broken down during activity, placing a greater emphasis on replacement. Here, it is interesting to note that some studies have found that athletes will become more efficient with regard to protein turnover and “waste less” after training.3

Most research suggests that athletes ingest sufficient protein in their usual diet, and that, given a sufficient intake of energy from other sources, lean body mass can be maintained within a considerable range of protein intakes.1 For these and other reasons, scientists have found that specific guidelines on the amount of protein to ingest are difficult to formulate.2

It is generally recommended that average people need 0.8g/kg of body weight. A kilogram is 2.2 lbs., so a 154 lb. person is 70 kg, and would therefore need 56 grams of protein in a given day. To translate this into pounds, someone would only need 0.36 grams per pound of body weight per day(g/ lb b.w.).

Some supplement companies commonly recommend 1g/ lb. of body weight, or nearly three times this amount. Some scientists believe that endurance athletes need about 1.2 to 1.8 g/ kg body wt or 0.55 to 0.82g/lb b.w. So, if we split the difference between these two values (1.5) we arrive at 0.68 g/ lb b.w., or the ingestion in grams of approximately two-thirds of a person’s weight in pounds. So, if we had a male athlete at 180 lbs., he should consume 120g of protein a day.

To calculate how many calories (kcal) to consume or what percentage of the total calories should be consumed, it can sometimes come as a surprise. Each gram of protein is the equivalent of 4 Kcals of energy. So, 120g x 4 kcal=480 calories of protein a day for a 180 lb. endurance athlete. Many endurance athletes of that body consume between 2,500 and 3,000 calories. So, 480/ 2500= 19% and 480/3000=16% of the total calories should be in the form of protein.

Recommendations for strength athletes are about the same, though a bit higher (1.6-1.7g/ kg body wt). On a per-pound basis, this amounts to 0.75 g/ lb of body weight. In other words, someone should consume three-quarters of his or her body weight — in grams of protein. The same 180 lb. person now needs 135 grams of protein per day or 540 calories. Because strength athletes are not expending as many calories per pound of body weight during training, they should consume fewer total calories.

So, if a 180 lb. strength athlete was consuming about 2,200- 2,500 calories, the percentage approaches 21-25% of the total calories. Some studies have shown that, in order to maintain nitrogen balance, endurance athletes require 1.2- 1.4 g/kg b.w. and strength athletes need 1.5 g/kg b.w. Researchers have also found Tour De France athletes who exercised 3-7 hours each day at high intensities were still able to meet their protein needs by consuming only about 12% of their total caloric consumption — about 6,500 calories.

Some research has found that some bodybuilders and weight lifters will consume well in excess of 3.0 g/ kg b.w., or 1.36 g/ lb of body weight. Translated to body weight, this means a 250 lb. bodybuilder will sometimes consume 341 g per day or about 1,363 calories of protein. This is far in excess of what is actually needed and can lead to health problems if continued on a long-term basis.


References

1. Tipton, Kevin D., and Robert R. Wolfe. “Protein and amino acids for athletes.” Journal of Sports Sciences 22.1 (2004): 65-79.

2. Millward, D. Joe. “Optimal intakes of protein in the human diet.” Proceedings of the Nutrition Society 58.2 (1999): 403-414.

3. Butterfield, Gail E., and Doris H. Calloway. “Physical activity improves protein utilization in young men.” British Journal of Nutrition 51.02 (1984): 171-184.

4. Phillips, Stuart M. “Dietary protein for athletes: from requirements to metabolic advantage.” Applied Physiology, Nutrition, and Metabolism 31.6 (2006): 647-654.

5. The Molecular Bases of Training Adaptation. Coffey, Vernon G; Hawley, John A. Sports Medicine: 2007 – Volume 37 – Issue 9 – pp 737-763

6. Lemon, Peter WR. “Effect of exercise on protein requirements.” Journal of Sports Sciences 9.S1 (1991): 53-70.