Endurance training can cause a significant amount of damage to your body’s tissues, cells, and other vital structures, which can increase with longer, more frequent and higher training intensities, and also low muscle glycogen.
So it makes sense that endurance athletes would need to consume protein to not only help repair this damage, but to also maximize the gains and adaptations from their training, and the research has shown this to be true.
The question is: how much protein do endurance athletes need?
The latest research highlights that other factors significantly affect the metabolic impact of dietary protein, including the type of protein and timing of consumption. All 3 aspects of protein intake (amount, type, and timing) can significantly affect the ability of tissues to repair the damage from training and build the new cellular and intracellular structures needed for improved performances.
But first, what is dietary protein? It’s a key macronutrient (meaning nutrients the body needs in large amounts), which is needed not only for repairing, maintaining and building the muscle proteins directly responsible for muscular contractions (actin, myosin, tropomyosin, and troponin), but is necessary for our DNA, forming new red blood cells, hormones, neurotransmitters, the immune system, and much more.
Consuming protein in our diet is important for making other key proteins such as enzymes, which are essential for the biochemical processes that break down carbohydrates and fats into smaller parts which can then be utilized to make energy
Because consistent aerobic training results in, amongst other things, an increase in the amount of these energy producing enzymes (and the number of mitochondria, where many of these enzymes are found), there is a need for consistent protein intake over the duration endurance athletes are training.
So for endurance athletes, dietary protein is key to repair and building new structures in muscle for increased muscle contracts as well as increasing the muscles ability to generate the energy needed for muscular contractions.
Proteins are large molecules made up of individual amino acids joined together to make a long chain. And it is actually these individual amino acids that the body uses, not whole proteins from our diet, to repair existing and to make new proteins. A protein is analogous to a brick building with the individual bricks being equivalent to individual amino acids bonded together to make the walls of the building. When we consume protein in our diet, they are broken down in the digestive system into these individual amino acids or up to 3 amino acids joined together.
These small molecules are then able to be absorbed into the blood and used throughout the body to make new proteins.
There are thousands of different proteins found in the human body and each is a different combination of just 20 amino acids. The reason why some proteins can provide increased benefits over others is due to the differences in their combination of amino acids. Amino acids are grouped into 3 categories: Essential, Non-Essential and Conditionally Essential.
9 amino acids are classified as essential because the human body isn’t able to make them but they are needed by a host of various tissues and systems to function normally. If we don’t consume enough essential amino acids our health suffers in many ways such as decreased mental and physical energy, various growth and development disorders, and protein deficiency diseases such as Kwashiorkor. In the United States, this is unlikely as most American Adults meet or even exceed the recommended daily intake of protein, which is likely to include sufficient essential amino acids.
The human body is able to make 4 amino acids that are considered non-essential to our diet, meaning it not essential for us to consume them because our body is able to make them in sufficient amounts for us to remain healthy.
And the last 7 amino acids are classified as conditionally essential meaning that under normal circumstances it is not essential to consume them in the diet but during certain times, such as illness and stress (and exercise is considered a stress to the body), it may become necessary for the body to have them in higher amounts than the body can manufacture. So during these times of heightened stress we must consume these conditionally essential amino acids, or the proteins that contain them, in our diet in order to stay healthy.
So from this we can see that the types of proteins that have essential and conditionally essential amino acids, and higher amounts of them, are particularly important for our health. Remember, as an athlete, health is the foundation of all performance, because if you’re not healthy you can’t train or race at your best, or you may not be able to train or race at all for a period of time.
Aside from maintaining our health, there are certain high performance amino acids that have been shown to preserve glycogen stores and help limit catabolism, even play a role in increased muscle protein synthesis following exercise, if consumed in the right doses before, during or after exercise. The 3 branched-chain amino acids (BCAAs) leucine, isoleucine and valine (a sub-group of the essential amino acids), are 3 such amino acids.
Leucine in particular, is perhaps the most extensively researched and tested of these high performance amino acids. For example, during prolonged exercise, BCAAs are preferentially broken down and used for fuel in skeletal muscle compared to other amino acids.
Leucine plays a central role in these processes and it has been shown that lower levels of leucine in the muscle cells may be associated with the decrease in protein synthesis that occurs during exercise19. It’s not surprising then that if the BCAAs are consumed immediately before or during prolonged endurance exercise they may reduce the breakdown of muscle proteins which would normally be used to provide amino acids for fuel. Leucine consumption, along with other essential amino acids, during moderate intensity endurance, has also been shown to enhance muscle protein synthesis after exercise. So while leucine, and the other BCAAs, may not directly enhance endurance performance as previously thought, it does appear to additional exercise related benefits in a number of ways.
With that in mind, let’s go back to our original question: how much protein do endurance athletes need?
Endurance athletes undertake significantly more physical activity than the average person, and being more active also means they cause significantly more damage to their body that needs to be repaired. Numerous research groups have shown that the current recommendations for protein intake for average American adults are insufficient for highly trained endurance athletes and recommend they consume 50% or more protein than their sedentary peers.
An accepted recommendation for the average American adult is to consume 0.36 grams of protein for each pound of body weight (or 0.8 grams per kilogram body weight) each day to meet the basic nutritional needs to stay healthy. So if a person weighs 170 pounds then they should consume a total of 61.8 grams of protein every day to stay healthy (170lbs x 0.36 = 61.8g).
For endurance athletes, who are significantly more active than the average American adult, it has been recommended that they consume 0.5 to 0.8 grams per pound of body weight (or 1.2 – 1.7 grams per kilogram body weight). And some researchers suggest it should be even higher (0.83 grams per pound or 1.83 grams of protein per kilogram body weight) depending on the volume, intensity and types of training.
Where each endurance athlete falls in this range of protein intake is directly related to the amount and intensity of training they are undertaking, as well as their training status (beginner, intermediate, advanced, elite). Training more frequently, for longer durations, or at higher intensities all increase the amount of damage to the bodies tissues, and so increase the need for repair and adaptations. The type of training also matters. For example, running on concrete will do more muscle damage than swimming or cycling, especially running downhill which has a higher eccentric loading of the muscles. (Eccentric means there is an increased tension in the muscle as it is lengthening, which basically means the muscles are slowing down or stopping the movement, which in this case is occurring as your leg muscles, specifically your quadriceps, are trying to slow your body from falling down the hill!)
Compared to the more sedentary average populations, it makes sense that endurance athletes would need to consume more protein, and those endurance athletes who are training most, if not all, days of the week, including high-intensity aerobic training, longer distance training, and high-intensity resistance training these higher intakes may be needed. (Yes, endurance athletes should be engaged in resistance training.)
To determine more specifically how much protein an athlete needs will require some experimentation. First step is to determine where you are currently by completing a 3 day dietary recall. There are various apps that can help you out.
Once this has been figured out, determine if you are recovering as quickly as you would expect. If you’re not, increase your intake by 10-20% and maintain your training duration, intensity and frequency for 2 weeks and reassess your recovery. If you are recovering well and your protein intake is on point but you are about to increase your training intensity, duration or intensity, again look at increasing by 10-20% and over the next 2 weeks of increased training and see how you recover.
That said, it’s not as simple as taking in more protein as your training needs increase.
Endurance athletes should also be aware that not all proteins are created equal. Some increase the rate of protein synthesis, while others can increase protein synthesis for significantly longer
Different types of proteins such as whey and casein from milk, egg, soy, and others, have different amounts and types of amino acids and different rates of digestion, which cause the rate at which their constituent amino acids appear in the blood to differ, which in turn affects things like blood insulin levels.
Insulin is an important hormone which not only affects sugar or glucose uptake from the blood into tissues such as muscle, but also affects amino acid uptake as well.
Because of these differences, proteins affect muscle protein synthesis in different ways and to greater or lesser degrees. For example, even though whey, casein and soy are classified as high-quality proteins, when the same amount of whey protein is consumed it is more rapidly digested and results in a greater rate of muscle protein synthesis.
This increase in protein synthesis has also been attributed to the higher leucine content of whey compared to the other proteins in young and older individuals. As discussed earlier, higher leucine intake, in this case because of the higher content in whey, not only increases protein synthesis to a greater extent but also causes a higher insulin response than other proteins like casein23. A higher blood insulin concentration is important because insulin increases the uptake of amino acids and glucose from the blood into muscle which increases rates of protein synthesis. So choosing whey protein to maximize recovery, for example when there is only a few hours between training sessions, can be very beneficial.
In spite of that, don’t write off other proteins just yet. There are also benefits of consuming proteins such as casein which take longer to digest. Casein does increase protein synthesis just not to the magnitude of whey, but the response from whey is short lived whereas the increased protein synthesis from casein remains elevated as whey decreases back to resting levels.
This prolonged response can provide a great opportunity to enhance the repair and adaptation processes overnight by consuming protein in the hour prior to sleep, which may be especially important to athletes who train in the evening.
Remember: timing is everything! Well, maybe not everything, but it is a very important aspect of optimizing the effects of dietary protein that arguably may be more important than simply consuming the recommended daily protein intake.
For example, there is some evidence that consuming a moderate amount of protein with every meal, as opposed to consuming a disproportionate amount with the evening meal, may result in greater protein synthesis over a 24 hour period. There is also some evidence from ongoing research to support that it may be more beneficial to spread protein throughout the day in older adults as well.
In terms of timing around exercise, there is some scientific evidence that if whey protein and leucine are added to carbohydrates and consumed before short (6 second) high-intensity cycling sprints, that protein synthesis after the exercise is significantly increased.
The majority of the current research doesn’t show improvements in endurance performance when protein or amino acids, with or without carbohydrates, are consumed during exercise. This is despite the evidence that the breakdown of amino acids for fuel during endurance events has been shown to provide up to 10% of the total energy requirements. So the benefits of adding protein or amino acids to carbohydrates during prolonged exercise, are potential increases protein synthesis and decreases protein breakdown during and after the exercise session.
Research has shown that muscle protein synthesis and breakdown are elevated after a single bout of endurance exercise. But if protein is ingested immediately afterwards then the amount of protein being made is more than the amount being broken down from the training. If protein consumption is delayed until 3 hours after endurance exercise has finished, then significantly less amino acids are carried into the leg muscles and muscle protein synthesis is less than if it was taken immediately after exercise.
This, and other similar research, has led to the recommendation that protein and carbohydrates should be consumed within 30-60 minutes post-exercise. The culmination of research using different amounts of protein in both endurance and resistance training studies in this time period immediately after exercise has also shown that 20-25g of protein is the optimal amount recommended.
For endurance athletes, when it comes to protein, it is also worth noting that if the body’s stores of carbohydrates (glycogen) are low before an exercise session, such as training in the morning on an empty stomach, muscle breakdown and the use of amino acids for energy is significantly increased.
Unfortunately, training in the morning on an empty stomach is a common practice for many endurance athletes. Similarly, some high-volume athletes may not have enough time to consume sufficient carbohydrates between their morning and lunch time training sessions. So in these cases it becomes even more important to consume 20-25g of high-quality protein (and carbohydrates) immediately after training, to optimize repair and adaptations.
There are other times throughout the season, not just before, during or after a single exercise session, when endurance athletes should increase their protein intake, such as aiming to decrease body fat. Unfortunately, many athletes not only reduce their total caloric intake by decreasing the size of meals or skipping snacks, but in doing so typically decrease their protein intake as well. And while the goal is to decrease fat mass, an unintended consequence can be the loss of muscle mass, and with that loss of muscle they may experience decreases in strength, power and endurance, and poor race performances. Research has shown, however, that in different athletes, increasing protein intake above the daily recommendations to more than 0.57 grams per pound body weight per day (>1.25 grams per kilogram body weight), helps maintain muscle mass when in a caloric deficit.
For endurance athletes who need to increase their protein intake, they often ask: “Do I need to take protein supplements?” After all, consuming whole foods sources of protein such as ground beef have been shown to increase protein synthesis with exercise.
The answer is quite often no, you don’t need to use protein supplements such as a whey or combination protein powder.
There are many whole food sources such as dairy, eggs, meats, rice and beans, that will provide the amount and type of protein to maximize gains. And it is also important to recognize that supplements are designed to be just that, a supplement to a balanced whole food diet. That said, there are many positive situations where protein supplements are a viable option for many athletes.
Convenience. Transporting and keeping milk, eggs or other whole protein sources in a cooler at the track in summer, for some athletes requires more planning than a ready to drink protein drink, water and protein powder, or a protein bar. All are good options, and some are more practical than others for different athletes. Sometimes it can also be a nice and simple change to pack a protein drink, bar or powder rather than make a meal or snack.
Taste. A tall glass of cold milk is awesome! And smoothies can be a great way to include nutrient dense berries and an added kick of flavor. Protein supplements also come in a variety of flavors which can alleviate the boredom some athletes experience when consuming a high volume of foods to meet their caloric needs.
Volume. Highly competitive and elite endurance athletes are expending enormous amounts of calories every day, often 2-3 times the average person. Consuming a sufficient amount calories in the form of whole foods can be physically difficult given the size of the athlete’s stomach and the physical size of these foods. Again, smoothies and other liquid calories can be very helpful for these individuals, as can protein supplements which are rapidly digested and absorbed, such as whey.
In summary, endurance athletes need more protein than the average person, and that is typically somewhere in the range of 0.49 to 0.7 grams per pound of body weight (or 1.12 – 1.6 grams per kilogram body weight). Athletes should look at their current diet and training to determine where they fall\ in that range. It is also recommended that endurance athletes consume 20-25g of easily digested high quality protein such as whey, with carbohydrates within 30-60 minutes after training. During times of intensified or increased volume of training, consuming casein before bed can enhance recovery. Consuming at least 0.57 grams per pound body weight per day (>1.25 grams per kilogram body weight) can also help to maintain muscle mass when in a caloric deficit to decrease body fat.
Carwyn Sharp, PhD, is a recognized expert in endurance sports who has authored and co-authored numerous book chapters, scientific articles and abstracts, and presented at international and national conferences and clinics on endurance sports topics such as nutrition, strength and conditioning, training and physiology.
Dr. Sharp has degrees in exercise physiology (BS, MS) and nutrition (PhD) and has been coaching athletes from beginner to Olympic medalist for almost 20 years. He has been a certified coach in strength and conditioning (CSCS), triathlon (USAT L1) and track and field (USATF L1), with a personal best marathon of 2:46.