By Peter W.R. Lemon, PhD E-mail: plemon@julian.uwo.ca
There has been debate among athletes and nutritionists regarding dietary protein needs for centuries. Although contrary to traditional belief, recent scientific information collected on physically active individuals tends to indicate that regular exercise increases daily protein requirements; however, the precise details remain to be worked out.
Based on laboratory measures, daily protein requirements are increased by perhaps as much as 100% vs. recommendations for sedentary individuals (1.6-1.8 vs. 0.8 grams /kilogram). Yet even these intakes are much less than those reported by most athletes. This may mean that actual requirements are below what is needed to optimize athletic performance, and so the debate continues.
At the present time, substantial data indicate that the current recommended protein intake should be adjusted upward for those who are physically active, especially in populations whose needs are elevated for other reasons:
For these latter groups, specific supplementation may be appropriate, but for most North Americans who consume a varied diet, including complete protein foods (meat, eggs, fish and dairy products), and sufficient energy the increased protein needs induced by a regular exercise program can be met in one's diet.
In recent years, the multiple and varied health benefits resulting from regular physical activity have become well documented; as a result, recommendations for increasing one's exercise level are becoming commonplace. Although athletes, especially those heavily involved with strength training, have long believed that their protein intakes must be much greater than for those who are sedentary, this opinion is derived via nonscientific means.
In contrast, the current recommended dietary allowance (RDA) for protein does not recognize any increased protein need for a physically active lifestyle. However, even this scientific recommendation could be incorrect, as it is based on data collected from physically inactive or, at best, minimally active individuals.
Throughout most of the 20th century, it has been assumed that physical exercise was an insufficient stimulus to alter protein needs significantly, even though this question had not been examined systematically in the scientific literature.
In light of the new physical activity recommendations, it is particularly important to know if regular exercise increases dietary protein needs because, if so, following these guidelines could lead to significant health problems related to sub-clinical/clinical protein deficiency.
The current recommended protein intake could be sub-optimal for those who regularly exercise. Fortunately, there is substantial recent scientific information collected on physically active subjects (completed after the current US recommendations were published), and much of this suggests that regular physical activity can increase protein needs.
Factors Which Appear To Affect Dietary Protein Need
It has been known for about half a century that inadequate energy intake leads to increased dietary protein needs, presumably because some of the protein normally used to synthesize both functional and structural tissue protein is utilized for energy under these conditions.
Apparently, this effect on protein need is similar when the energy deficit is caused by increased energy expenditure such as exercise. In fact, this effect could be even more dramatic in those who are physically active, as protein needs are likely already increased in order to maintain a greater protein synthetic rate due to the presence of greater absolute strength or endurance in athletes.
Exercise Intensity, Duration and Type
Increasing exercise intensity and duration, at least with aerobic endurance exercise, causes increased use of protein, presumably as an auxiliary fuel. Based primarily on nitrogen balance experiments, this results in an increased daily protein need of about 50% to 75%.
Although heavy resistance (strength) exercise appears to increase protein need by about 100% based on nitrogen balance experiments, isotope tracer studies have revealed that the underlying mechanism is not increased fuel use. Rather, it is the result of changes in muscle protein synthetic rate and the need to maintain a greater overall muscle mass.
Although strength athletes can increase muscle growth with supplemental protein, this effect seems to attain a plateau at protein intakes (1.4 g/kg) far below intakes typical of experienced bodybuilders.
Protein Quality
It is well known that humans can synthesize only about 50% of the necessary amino acids that make up the proteins in our bodies. Therefore, if the remaining amino acids (called indispensable or essential) are not consumed in sufficient quantities, protein production is affected adversely.
The quality of protein in a food is determined by its indispensable amino acid content. Some foods contain all of these indispensable amino acids and in amounts sufficient to maintain protein synthesis, while others are lacking in at least one amino acid. The former are called complete protein foods and include such foods as dairy products, eggs, meat and fish, while the latter include grains, vegetables and fruits.
Although it is also possible to obtain sufficient indispensable amino acids from a diet that excludes complete protein foods entirely by combining grains, vegetables and fruits, this requires some knowledge of which foods to combine. As a result, vegetarians, especially those that exclude eggs and dairy products, when they adopt a physically active lifestyle constitute a group that is likely at greater risk for insufficient dietary protein intake.
Moreover, it has been shown, at least in 59 to 69 year-old men, that strength training produced greater muscle mass gains with a meat-containing diet in comparison to a lactovegetarian diet. These data suggest that type of protein may play an important role in muscle growth with strength training.
Recommendations
A variety of factors interact to increase dietary protein needs of individuals who exercise regularly. Current research indicates that as long as energy intake is adequate a daily protein intake of 1.2-1.4 g/d for individuals participating in regular endurance exercise and 1.6-1.8 g/kg for their counterparts involved in strength exercise should be sufficient.
To ensure these increased needs are met, care should be taken to consume a diet containing adequate energy and a selection of high quality protein foods, i.e., dairy products, eggs and meat. Select populations may be at increased risk of not consuming sufficient protein due to increased requirements for a variety of other reasons, i.e., unbalanced diet (vegetarians), inadequate energy intake (dieters or athletes with high energy expenditure, especially women), higher baseline requirements (those who are growing or the elderly) and so on.
Journal American College Nutrition October 2000;19(5 Suppl):513S-521S (Full Text Article)
Many people are confused about protein intake, especially with recent fear-generated hype about the Atkins diet causing kidney damage.
Let me first translate the above recommendations from the metric system to our English system.
A typical adult weight is 150 pounds, which translates to 68 kilograms (150 / 2.2).
So a 150 person who does aerobic exercise would need 88 grams per day and that is 30 grams per meal.
That amount increases to 115 grams for someone who does weight training and that would be about 40 grams per meal.
While I am not a proponent of taking any more protein, or food, than is necessary, as this will clearly be counter-productive, it is my experience that most individuals do not consume enough protein. This is in spite of the commonly held believe that Americans consume too much protein.
I see this most frequently with egg use. Most people should consume between four and six eggs at one setting to obtain enough protein, as each egg only has 6 grams of protein. If you are concerned about eating all these eggs you should review the article I posted earlier on eggs. Ideally the egg yolk should not be mixed with the white as in scrambled eggs, but cooked very gently to avoid breaking it down. Steam poaching is probably the best way to cook eggs and the yolk should be runny.
However, I do recommend consuming the yolks uncooked, as that will provide you with maximum nutritional benefits. No need to worry about salmonella if you have a healthy GI tract, as for the most part it is a self-limiting illness that is easily treated with large doses of good bacteria. The best eggs are from chickens that are given flax seeds for at least four weeks, as that will convert to high levels of omega-3 in the egg.
It is also important to remember to cook your egg whites so you won't acquire a B vitamin deficiency.
While it takes a considerable amount of eggs to reach required protein intakes, meat servings can be considerably less. One ounce of meat typically has about 8 grams of protein. So most of us would need about 3-6 ounces of meat per meal, depending on our exercise requirements.
Amount for 20 grams (Non-exercising typical woman)
Amount for 30 grams (Non-exercising typical man)
* (not recommend due to high mercury content)