I came across this paper a few days ago, and figured it might be useful to recap its highlights.
It’s titled, ‘Is There a Need for Protein Ingestion During Exercise?‘ from the Gatorade Sports Science Institute by Luc J.C. van Loon.
I’m going to skip most of the parts that don’t relate specifically to endurance exercise at this point.
First, though, a quick, crude recap of what protein is in the first place.
Proteins are made up of many smaller “building-block” molecules called amino acids. These many amino acids are joined together in many different ways, making up many different protein structures that are important for the proper functioning of our bodies.
There are two types of amino acids: Essential Amino Acids, and Nonessential Amino Acids.
Essential Amino Acids are the ones that we cannot manufacture in our bodies, and therefore it is essential that we consume them in our diets. It is important that these essential amino acids come from ‘complete’ protein sources, which means that the essential amino acids will be contained in relatively equal amounts, ensuring proper absorption.
Nonessential Amino Acids are the ones that our bodies can make in the amounts that we require them, though it is still important to consume them (and they will often come along with the Essential Amino Acids in food).
Some amino acids will be “conditionally essential” which means that sometimes we will not be able to make them in high enough amounts, like during times of stress.
When you eat a protein-containing food, like a steak, the proteins will be broken down during digestion into the individual amino acids. These amino acids will enter circulation and will be used as needed by our bodies. The level of circulating amino acids will drop off as they are used by various cells (for things like muscle protein synthesis, antibodies, neurotransmitters, enzymes, hormones, etc.) and will be replenished when we eat more protein-containing foods.
During exercise that requires intense muscular contraction, there will be an increase in protein breakdown, and so the circulating level of amino acids will drop down, which is why it’s especially important to consume protein postexercise.
Alright, on to the article:
“Consequently, it has been debated whether dietary protein administration prior to and/or during exercise can also stimulate muscle protein synthesis rates during continuous endurance type exercise activities. Prior work has clearly shown that protein co-ingestion during prolonged endurance type exercise improves whole-body protein balance. Moreover, whereas whole-body protein balance remained negative when only carbohydrates were ingested, dietary protein co-ingestion was shown to improve whole-body protein balance by increasing protein synthesis as well as decreasing protein breakdown, resulting in a positive protein balance during 5 h of prolonged endurance exercise.”
What this means, basically, is that ingesting protein during exercise will help make sure that the circulating pool of amino acids does not deplete significantly. When there is a negative protein balance, more proteins are being broken down than are being synthesized. A positive protein balance, then, would mean the opposite; a state wherein the breakdown of proteins does not exceed the amount being synthesized. This, however, does not mean that the muscles specifically have an increased rate of protein synthesis during exercise, as whole-body protein synthesis and muscle protein synthesis are not the same thing.
The author goes on to mention
“As measurements on a whole body level do not necessarily reflect skeletal muscle tissue, a follow-up study was performed to assess muscle protein synthesis rates during endurance exercise while ingesting carbohydrate or carbohydrate plus protein. Interestingly, this study showed that muscle protein synthesis rates were higher during exercise when compared to pre-exercise fasting protein synthesis rates. However, no significant differences were observed in muscle protein synthesis rates between the carbohydrate and carbohydrate plus protein trial, despite clear differences in whole-body protein balance. Future studies are warranted to assess muscle protein synthesis rates during more prolonged exercise, as longer exercise trials (>3-5 h) will allow differences in fractional protein synthesis rates to become apparent. Clearly, more work is needed to address the relevance of the potential to stimulate muscle protein synthesis during resistance as well as endurance type exercise activities…”
I still think that providing some protein during a training session could be useful, especially for running, due to the excessive eccentric movements which will contribute further to muscle damage than concentric movements would. If a training session is long enough to warrant fueling, then I think it’s safe to say that it’s long enough to ingest some amino acids. This could even just be Branched-Chain Amino Acids, or specifically Leucine, a particularly anabolic amino acid.
Training aside, I think it is probably important to get in some protein during a race that lasts longer than a few hours as well. Not specifically for ergogenic benefits — the jury is still out on whether or not there are any — but simply to prevent some muscle damage and potentially improve recovery. Endurance athletes are especially susceptible to muscle-loss with excessive training. This is just an adaptive response, unfortunately, but doing what we can to mitigate this response will be helpful for long-term health. Hence my recommendation for protein consumption.
The author does end up saying something similar:
“…Therefore, protein ingestion prior to and/or during prolonged exercise training sessions may inhibit muscle protein breakdown, stimulate muscle protein synthesis and further augment the skeletal muscle adaptive response to exercise training. Protein co-ingestion during exercise does not acutely improve performance capacity, but may improve exercise training efficiency.”
In conclusion, if you’re training long enough to require carbohydrate fueling, add some BCAA or Leucine to the mix, and it may potentially improve recovery. But, more importantly, it may work to improve long-term muscular and metabolic health by preventing muscle-loss. And don’t forget to eat plenty of protein throughout the rest of the day!