Protein during Exercise

Here at TORQ, the functionality of every product we produce is backed up by a sound level of peer reviewed independent research.  This is something we spend a lot of time looking into before we even consider launching a product. It is an essential part of our philosophy but, also equally as  important to us, is that we don’t mislead the public and create hysteria around a product just for potential  ‘sales’. If the research supports a performance benefit, we’ll make that product and, if it doesn’t, we won’t. It sounds pretty logical, but unfortunately, when the marketers get their hands on a sports nutrition product, the benefits of its use can be spun into a spider’s web of customer entrapment. Benefits can be exaggerated somewhat.

An example of this has taken place in recent years with the growth in the number of sports nutrition companies adding protein to energy drinks, designed for use during exercise, with claims of significantly increased endurance performance and better hydration. Having extensively reviewed the research, here at TORQ, we don’t produce such a product for a number of reasons summarised below:

  • Lack of scientific support – The research into protein use during exercise is still a very new area of research in sports science and, as yet, very few studies have really looked into the area. Although a few studies have shown a positive effect of performance during exercise, all of which had flaws with their methodology. A greater number of studies have shown no affect on performance.
  • Of the studies that have shown a benefit, none have proposed a feasible physiological mechanism to explain how protein would help performance during exercise when an athlete is fuelled properly with carbohydrate.
  • Protein makes up a very small proportion of the body’s fuel during endurance exercise and is not its preferred source of fuel.  It is also something the body already has stored in abundance.
  • Stomach upset during exercise can often be a problem for athletes trying to fuel optimally.  Protein requires a greater amount of digestion than carbohydrate and, when already saturating the stomach with vital carbohydrate, the addition of protein can result in the dreaded GI/Stomach upset and restricted absorption.

These are, in brief, the fundamental reasons why the intake of protein during exercise is not advisable but, to understand the full story, we have explained why taking on protein during exercise is simply not a good idea in detail below.

Before we even consider the research and what it shows, we look at the fundamentals of fuel metabolism during endurance exercise.  You will see why even some of the world’s top sports scientists were slightly bemused when claims were first made that the addition of protein offering a performance benefit to endurance exercise.

During endurance exercise, carbohydrate and fat are the body’s two main fuel sources. At low exercise intensity, fat is the major fuel source for the working muscle. Fat is a very efficient fuel; it is stored in abundance in the body and even very small amounts, when combined with oxygen, is able to produce a great deal of energy for the working muscle. As a very energy dense fuel source, that is stored in great quantities in the body, it is almost impossible to deplete the body’s stores unless exercising for a period of weeks.

Once the intensity of exercise increases and the aerobic system reaches its threshold for energy production (the point where the chemical reactions involved with burning fat cannot keep up with the requirement of energy from the muscle), the body begins to use the anaerobic system to reach the energy demands of the working muscle. This system burns exclusively carbohydrate as a fuel which is a very easy fuel for the body to utilise.  It produces a lot of energy very quickly and doesn’t require oxygen, but produces lactate as a by-product. The major crux of this system though is carbohydrate is something the body has a very limited store of and is a fuel that, when exercising hard, the body can burn through very quickly. We will come onto that in more detail shortly.

Now you may be starting to wonder where protein comes into this, and quite rightly so? Protein makes up a very small proportion (less than 5%) of the total energy expenditure of exercise and, as such, isn’t really that significant.  Even then, the only time that protein becomes a fuel source is when carbohydrate stores are completely depleted. Once this happens, the body begins to breakdown its proteins in the form of precious muscle, in an energy-sapping process called gluconeogenysis, to create carbohydrate. If adequate carbohydrate is provided in the first place, this process doesn’t need to happen at all – and it shouldn’t.

If an athlete goes into a training session with their carbohydrate stores fully topped up, they will have around 2000 kcal (500g worth) of carbohydrate stored in their muscles and liver.  These stores can be depleted in as little as 90 minutes when exercising at a moderate to high intensity and, when the body’s carbohydrate stores become fully depleted, there is a catastrophic drop in performance, often referred to as ”bonking” or “Hitting the wall”, which is not a good place for any endurance athlete to be! The main goal for an endurance athlete is to prevent this from happening and this can be achieved through a number of ways:

  • Train the body to be better at burning fat – By completing long steady training sessions which stress the aerobic system, we are able to increase our body’s ability to utilise fat as a fuel.  This means that carbohydrate doesn’t start to be used until a higher intensity of exercise and therefore “spares” the body’s precious glycogen reserves.
  • Carbohydrate load in the run up to the event – This forces the body to saturate its muscle and liver stores of carbohydrate, allowing more precious carbohydrate to be available and therefore allowing the athlete to exercise longer before “bonking”.
  • Fuel optimally for exercise – This is where energy drinks and gels come in; they allow you to take on board an exogenous (exter¬nal) form of carbohydrate that your muscles will use instead of your stored carbohydrate. Every gram of carbohydrate you consume from a food or drink source whilst exercising is a gram you’re not using from your stores, so this will extend the time to exhaustion.

On that last point, research has shown that an optimal carbohydrate intake is 90 gram per hour when utilising a 2:1 Maltodextrin:fructose mix, which is 40% more than in a traditional maltodextrin or glucose alone drink, the next best energy delivery system (60 grams per hour). For further information on the research surrounding this, click here.

This 90 grams of carbohydrate completely saturates the transporters in the gut, which drag carbohydrate into the blood stream.  Although any kind of carbohydrate fuelling will benefit the athlete above and beyond the use of water, the extra 30 grams of carbohydrate delivered through 2:1 Maltodextrin:Fructose spares the body’s limited endogenous (muscle and liver glycogen) stores further and allows the athlete to maintain their pace for longer, greatly enhancing endurance performance.

The most significant reason not to add protein to a sports drink during exercise is because of the problems associated with gastrointestinal (GI) upset/restriction of absorption. Protein takes the stomach much longer to breakdown than carbohydrate, so the addition of protein in an energy drink poses a significant risk of slowing down the absorption of vital, performance enhancing, carbohydrate in favour of protein, which is only really useful in the absence of carbohydrate.   The phrase “cutting off your nose to spite your face” comes to mind!  During exercise, combined with the limited stores of carbohydrate the body has, the gut has a very limited capacity to absorb carbohydrate, as all of the blood it normally relies on to digest food is diverted to the working muscles. This means that, during exercise, the gut has a limited capacity to process carbohydrate so the addition of protein will only slow this process down. Given that carbohydrate delivery is quite clearly THE limiting factor to endurance performance, we can’t think of any way that slowing down carbohydrate absorption could be of benefit?

From a sports science research perspective, the interest in protein as an addition to an energy drink all began when two researchers (Ivy, et al 2003 and Saunder, et al 2004) published their studies into the affects of additional protein on endurance performance.  The results from these showed that there was a massive, significant increase in endurance performance when protein was added to an energy drink. On closer inspection however, the studies used poorly designed protocols to test their theories, which did not replicate the normal conditions in which athletes train and compete and had previously been shown to be unreliable in detecting changes. This was also combined with them not having used trained athletes or having controlled participant diets in the run up to tests. Most significantly though, both studies were supplementing participants with relatively small amounts of carbohydrate, nowhere near the upper limits of what can be absorbed, and were adding protein in addition. This meant that participants in the carbohydrate-protein trial consumed more calories than in the carbohydrate only trial which, when combined with the low carbohydrate feeding, offered one very feasible explanation for the increase in performance, in that participants during the protein trial simply had more fuel and, as a result, performed better in the test. Had the carbohydrate-only group been ‘calorie-matched’ with the carbohydrate/protein group, the results would have been very different.

Since these two original studies, the same authors have both repeated their studies and found no affect. With the limited interest in the area, there has been little further research since the original publications, which has lead to a Meta-Analysis being published in 2010 (Stearns, et al. 2010). This took into account all of the relevant research in the area completed so far and statistically analysed all the results together and produced some very interesting results and conclusions.  In total, 11 studies were compared, only 3 of which had matched the amount of calories they had given participants, and only 3 of which had used a time trial protocol, which is the arguably the best form of test to use as it is the closest replication of normal training and competing. The Meta-analysis therefore concluded that, although there were some studies that did show an improvement in performance, this was simply a result of poor study design or adding more calories, rather than a unique benefit offered by adding additional protein. Protein could therefore be viewed as an unnecessary addition, if there is already an adequate CHO supplementation regime.

As well as the research providing a lack of adequate evidence for protein enhancing performance, no studies offered a feasible explanation for the mechanisms behind how protein could offer benefit, over a carbohydrate fuelling strategy alone (earlier in this article on the other hand, we have provided a very plausible explanation as to why carbohydrate-only preparations would work better). One of the most plausible explanations for how protein could offer a benefit during exercise was by preventing the breakdown of skeletal muscle.  However, a study from Germark, et al (2009) which, when comparing a carbohydrate only and carbohydrate protein drink, found no differences in protein metabolism.   One other potential suggested mechanism was that adding protein increased the oxidisation rate of carbohydrate, although this has also been shown not to be the case in a recent study by Rowlands and Wadsworth (2011).

So, essentially there is no conclusive evidence that the addition of protein in an energy drink during exercise will enhance performance in any way. Adding protein can be viewed simply as an unnecessary addition to an already good carbohydrate fuelling strategy and is best avoided because of its potential to cause stomach upset and reduce optimal carbohydrate delivery.

One feasible argument that we consider perhaps justifiable for using these kinds of drinks could potentially be for the rider who rides for several hours per day, every day (perhaps an ultra-endurance stage race or training camp) where meals are potentially being missed during the day and some protein intake during exercise would appear logical. Our argument against this practice would simply be that surely the athlete would benefit psychologically from a savoury low fat high protein snack periodically whilst riding rather than consuming a suboptimal soup all day? Ride on carbohydrate only, grab a lean ham sandwich and then get back to your carbohydrate feeding. In any event, this would be an extreme case indeed and most athletes don’t train like this. Moderate protein in the diet at the start and end of the day would be sufficient to cover the 12-13% of daily calories that should be allocated to protein for even the most extreme of riding. We feel that a rider would need to be exercising in excess of 8 hours per day every day to even consider taking on board any protein during exercise.


Cermak NM, Solheim AS, Gardner MS, Tarnopolsky MA & Gibala MJ. (2009) Muscle Metabolism during Exercise with Carbohydrate or Protein–Carbohydrate Ingestion. Med Sci Sports Exerc.  41(12): 2158–2164.

Rowlands DS & Wadsworth DP. (2011)  No Impact of Protein Coingestion on Exogenous Glucose Oxidation during Exercise. Med Sci Sports Exerc. Sept 16 [Epub ahead of print]

Saunders MJ, Kane MD & Kent Todd M. (2004) Effects of a Carbohydrate-Protein Beverage on Cycling Endurance and Muscle Damage. Med Sci Sports Exerc. (36): 1,233–1,238.

Stearns RL, Emmanuel H, Volek JS & Casa, DJ. (2010) Effects of ingesting protein in combination with carbohydrate during exercise on endurance performance: a systematic review with meta-analysis. J Strength Cond Res. 24(8): 2192–2202.

Ivy JL, Res PT, Sprague RC & Widzer MO.(2003) Effect of a Carbohydrate-Protein Supplement on Endurance Performance During Exercise of Varying Intensity. Int J Sports Nutr Exerc Metab. (13): 382–395.