During exercise, we typically think of carbohydrates and fats as our main sources of fuel, while protein is associated with recovery. Today, many sports nutrition bars, gels and drinks contain branched-chain amino acids (a special subset of amino acids) or protein. If we aren’t using protein to help muscles continue to make energy and contract, then what is protein doing in those supplements? Is there a role for protein during exercise? Let’s take a look.
Here’s a little background about the “normal” role of protein. This macronutrient is made up of amino acids bound together by a peptide bond, similar to how glycogen is just a bunch of glucose molecules bound together. Protein has many roles in the body including an important part of cell structure (like muscle), to act as important enzymes or hormones, carry other molecules in the blood as well as serve a direct and indirect role in metabolism. At the chemical level, proteins are not that different from fats and carbohydrates. Like those sources of fuel, they have plenty of carbon and hydrogen molecules but they have an added nitrogen group. Remove the nitrogen group and you have a molecule that looks closer to a carbohydrate and can be turned into fuel or used as an important metabolic intermediate in various metabolic pathways (and the nitrogen becomes urea that is disposed of via urine).
Studies which use “tracers” to follow the path of specific molecules clearly show that during exercise, branched-chain amino acids are also used by the mitochondria to create energy similar to fats and carbohydrates but to a much lesser degree, and the usage does not really go up during normal exercise in the fasted condition. So, in theory, it seems that proteins are used during exercise, but that doesn’t necessarily mean that the addition of protein to exercise will improve performance.
Knowing that carbohydrate is key during endurance exercise, researchers started looking at the role of protein by adding it to carbohydrate drinks consumed during exercise. In a ratio of 3:1 (carbohydrate: protein, in grams) a number of studies found that protein enhanced performance in “time to exhaustion” tests. Time to exhaustion tests are laboratory-based tests during which the subject exercises at a single workload (or speed) for as long as possible. For example, in one study they looked at how long cyclists could maintain an effort at 85% of VO2max after completing 3 hours at 45–75% VO2max on three separate trials. They found that regardless of the initial exercise intensity, the carbohydrate plus protein increased performance1. The result was verified by other labs and sports nutrition companies started adding branched-chain amino acids and protein to their sports nutrition products. So protein during exercise increases performance, right? Well, not so fast. The time to exhaustion performance test is problematic since most endurance races are not a time to exhaustion and instead cover a specific distance, thus the validity of this type of test to real-world performance is questionable. Exercise researchers have found that a time trial is a more valid laboratory test to simulate real-world race fitness. So how does added protein fare in those types of studies? Not so good as several studies using a time trial design found the addition of protein to a carbohydrate drink (assuming an adequate amount of carbohydrate) does not increase performance3. However, an important caveat is that some ultras are actually more like a time to exhaustion exercise test, mind over body, rather than a time trial. Furthermore, most of the studies only looked at two hours of exercise max, which is significantly shorter than the average ultra finish time.
While the data on protein directly improving performance is mixed, data on protein during exercise improving performance in subsequent exercise is clearer. The addition of protein during exercise (or soon after) has an added benefit of creating a positive net protein balance environment, which basically means more making-new-muscle proteins than breaking-down proteins. Specifically, the ingestion of protein seems to selectively decrease protein degradation rather than enhancing protein synthesis. The positive protein balance is associated with improved performance the day following exhaustive exercise and might prove useful for athletes completing multi-day stage races or even really long ultra events that may take in excess of 24 hours2.
What have we learned? Carbohydrates and fat are still king when it comes to providing energy during prolonged exercise. However, including protein during exercise may indirectly improve performance at a later date by helping create an environment for expedited recovery.
- Ivy JL, Res PT, Sprague RC, Widzer MO. Effect of a carbohydrate-protein supplement on endurance performance during exercise of varying intensity. Int J Sport Nutr Exerc Metab 13: 382–95, 2003.
- Koopman R, Pannemans DLE, Jeukendrup AE, Gijsen AP, Senden JMG, Halliday D, Saris WHM, van Loon LJC, Wagenmakers AJM. Combined ingestion of protein and carbohydrate improves protein balance during ultra-endurance exercise. Am J Physiol Metab 287: E712–E720, 2004.
- van Loon LJC. Is there a need for protein ingestion during exercise? Sports Med 44 Suppl 1: S105-11, 2014.