Most endurance athletes would agree that carbs are important, and to be fair, it’s probably the nutrient I talk about most to people. Carbs are key, and rightly should be front of mind for all endurance athletes. This may be the case but other nutrients, like protein, play an important role. With a little more thought and effort, optimizing protein intake can make a big impact of athlete’s health and performance.

What foods is it found in

The protein we ingest is broken down into amino acids in the stomach. These amino acids are absorbed and circulated around the body. Protein serves many functions such as creating structure, motion, enzymes, hormone production, and wound healing.

Good sources of protein can be found in both animal and plant-based foods. Humans require essential amino acids (EAAs), which they cannot synthesize themselves. Animal proteins contain all the essential amino acids. Plant proteins contain varying amounts of the EAAS, so consuming variety with several different types of plant-based proteins becomes key.

Most vegans are probably sick of the question: where do you get your protein from? In reality, it’s absolutely possible to meet your protein needs following a plant-based diet. It may, however, take a more thoughtful effort to achieve higher intakes, especially for those involved in heavy training programs.

Breakdown during endurance exercise

Muscles are constantly being broken down and rebuilt throughout the day. The fluctuation between building and breakdown depends on the timing and the dose of the ingested protein. The buildup of muscle tissue is known as muscle protein synthesis, and the degradation of muscle is known as muscle protein breakdown. Ideally, athletes looking to gain muscle or strength are looking for a net positive balance between synthesis and breakdown.

While not considered a primary energy source, protein does contribute as a fuel source during exercise. It’s estimated that <5% of total calorie expenditure during exercise comes from protein metabolism. Out of necessity, an inadequate supply of a preferred fuel sources (i.e., carbs), or extreme, prolonged exercise causes the body to use a higher proportion of protein for exercise. These numbers can be up to 10-15% of total calorie expenditure. While protein can be used, it is not preferred. The increased protein breakdown being the reason for higher protein requirements of endurance athletes. Without proper replenishment and repair of muscle, positive training response would not occur.

How much is needed

The current Recommended Daily Allowance for adults in the United States is 0.8g/kg protein per day. If you’re used to the US system and don’t know your weight in kilograms, divide your weight in pounds by 2.2. With the standard American diet, most people are meeting or exceeding the RDA. But the recommendation for athletes is a bit more variable. Depending on age, frequency, and intensity of a training program, current recommendations for endurance athletes sit at roughly 1.2-1.7g/kg protein per day. For a 160lbs athlete, this equates to a range of 87-124g protein.

Both the RDA and recommended range for athletes have been based on the amount of protein required to achieve nitrogen balance. Nitrogen is a component of amino acids. By measuring a person’s nitrogen intake and losses, one can determine a person’s protein requirements. In periods of growth, there will be positive nitrogen balance. In periods of wasting or extended fasting, there will be negative nitrogen balance.

Some athletes probably aren’t trying to achieve nitrogen balance. Nitrogen balance assumes no change in protein stores but gaining muscle would require positive nitrogen balance. Some athletes may benefit from higher intakes, up to roughly 2.5g/kg protein per day. This becomes especially true when athletes are trying to lose weight while maintaining muscle mass. I’ve even heard some recommend athletes consume 15-20% of total calorie intake regardless of activity level. Which, for the general exercising population, would give recommendations withing the 1.2-2.5 range. However, for those with extremely high calorie requirements due to large training volumes, this could require intakes of over 3g/kg. Given the increased muscle protein breakdown during endurance exercise, I can understand, in theory, how this could be valid. However, more research is needed. And athletes with this high of requirements are likely a very small subset of the population (although possibly a high percentage of professional endurance athletes).

Generally, 20-40 grams is enough to stimulate muscle protein synthesis. Athletes should aim to consume this amount every 3-4 hours to maximize their time building protein stores. Additionally, the essential amino acid, leucine, may hold special importance and is favorably used to stimulate muscle protein synthesis. If possible, athletes should choose protein sources rich in leucine such as whey protein powder, milk, eggs, cheese, beef, tuna, or chicken.

Timing

I find its usually the pros who do the worst job of protein distribution throughout the day. Time and time again I hear athletes talking about only consuming easily digestible carbs (rice, toast, etc.) during the day as to not deal with GI distress during sessions. While these food items are great sources of carbs, they offer limited protein (4g for one cup white rice, and 3g for one slice white bread). Avoiding protein-rich foods during the day, only to consume them late in the evening after completing the day’s training isn’t ideal.

The timing of protein consumed throughout the day may influence an athlete’s adaptations to exercise. Consumption of protein is required for muscle protein synthesis to occur. Long time periods without a protein feeding result in continued muscle protein breakdown, an undesirable outcome for most athletes. Protein accumulation and growth only occurs in the fed state. Frequent, consistent protein intakes every 3-4 hours seem to be best for muscle protein synthesis which is temporary and usually lasts between 1-4 hours.

In Relation to Carbs

At a population level, most endurance athletes will see the greatest performance benefit by consuming enough carbohydrates to support their training. If there’s one piece of advice I could give, it would be to focus on that. In my opinion, that’s where most could see the greatest benefit. It’s likely that most athletes, while maybe not consuming optimum levels of protein, can get by consuming lower levels of the recommended range.

Secondly, protein induces satiety, making you feel fuller. This increased satiety may impact an athlete’s ability to consume enough carbohydrate which, again, is the priority goal.

Inadequate carbohydrate intake with high protein intake is more likely to impair exercise performance than an adequate carbohydrate intake with lower protein intake. However, meeting optimum levels of protein can have a positive effect on body composition, recovery, strength, and other aspects of performance.

Photo: Jordan Rapp / Certified Piedmontese Beef