When thinking about how nutrition or more specifically one’s diet affects performance during a sporting endeavor coaches and other constituents seem to get stuck on the recommendations of a high or low carbohydrate diet. The concern that coaches and athletes seem to have is without enough carbohydrate intake sustaining performance, or improved performances may not occur. The concern is understandable because carbohydrate or what carbohydrate becomes in the body, glucose, is the underpinning for high-intensity actions (e.g., sprinting, explosive actions). The issue or debate is not that this macronutrient is not needed the discourse between coach and athlete should involve the questions; how much is required to sustain optimal performance, when should carbohydrate be consumed, and what type of carbohydrate?
The novice coach or performance specialist tends to lay down the gauntlet for an athlete by saying, “make sure to eat your carbs” or better yet, just orders pizza, jimmy johns sandwiches, or heavily breaded chicken dripping with grease laid over a helping of penne pasta. These types of actions most likely set the stage for behaviors that will last a lifetime with substantial weight gain and a life-long testament towards one’s self to get back to the way the body was when he or she was competing.
The problem with a general statement without complete understanding is the consequences that may lay the groundwork for behaviors that are unamenable later in life. The phrase, ” it is hard to teach an old dog new tricks” did not just occur one day it started because of this very reason. Once a habit is created, it is difficult to break. So where should one stand on the line of carbohydrate intake for athletes, more specifically for this post, soccer players? Lower carbohydrate diet or high carbohydrate diet?
In 2015, Josh Faga and I conducted a podcast with James Morton, a former nutritionist for Liverpool FC, on the Just Kickin It podcast (click here for podcast episode) where he discussed the three T’s: Type, Total, and Time. More specifically, the three T’s meant; the type of food consumed, the total amount of the food consumed, and the time the food is ingested. The three T’s have stuck with me ever since when advising or discussing an athlete’s diet.
The discussion with James Morton was fascinating, and I encourage readers to listen to the podcast we did with James. However, in a professional setting, many of the nuances associated with nutrition can be standardized when an athlete is in the care of a professional club (i.e., personal chef). In the college or university setting, the environment is much different, and athletes can get caught up in selecting the pasta dishes, pizza aisle, and topping it off with a colorful dessert. Oh-by-the-way these choices are all-you-can-eat.
So the question is how a soccer player should manage his or her diet so that performance can be sustained or improved? I dug into some research recently to examine what works and what doesn’t. I am not saying that scientific research is the end all be all by any means, but one has to start somewhere. First, randomized controlled trials should be the ‘gold standard,’ and a sample of the population of interest should be the main subjects for the research. There may be some small nuggets of information if the sample is from a different population or an animal study, but if you want to be able to infer outcomes to your population, it is necessary to find research examining subjects that represent your population.
Without an extensive review of the literature, I came across some research involving Rugby, Soccer and Australian Rules Football (AF). I found a statement made in the research conducted on Australian Rules Football players interesting because the authors postulate that AF presents higher workloads, since the player under examination used more muscle glycogen (e.g., AF player utilized 433 mmol/kg dw) which is larger than reported glycogen utilization in soccer and rugby, which where approximately 200 mmol/kg dw.1 One can posit that AF would be more demanding than soccer or rugby since the athletes tend to be larger, have more fat-free mass, and the duration of a match may be longer when you consider the time from start to finish, included injury time, halftime, breaks etc. of the competition. If one were to watch a Rugby match, there seems to be some overlap of the characteristics of the game compared to AF. Turning to Rugby, Bradley et al. (2016) found that manipulation of energy in the form of carbohydrate prescription did not appear to affect resting glycogen availability, glycogen utilization, or markers of match-play workload. In fact, a diagram showed that the players on the lower carbohydrate diet had higher levels of post-match glycogen compared to the players who consumed the moderate/high carbohydrate diet. There is some evidence suggesting a low carbohydrate diet may spare glycogen stores for moments specifically needed to perform high-intensity actions. Moreover, if adapted to a lower carbohydrate diet an athlete may increase non-esterified fatty acid production which may allow an athlete to increase fat oxidation rates during exercise at 80% of VO2max.2 Simply stated a player could spare glycogen, exercise at a higher intensity using fat oxidation, and possibly benefit from all the other aspects a low carbohydrate diet has been shown to produce (e.g., more fat-free mass, improved blood glucose levels).
Well, what about the research that demonstrates high-carbohydrate diets, which have been shown to improve performance? That is a valid question and one that I cannot wholly answer because every human being, complex system, is different. What I can say if one is examining the research to make a claim, make sure that calories are equated for in the research. If the calories are not equated, then the research cannot say that high carbohydrate diets are better than low carbohydrate diets. Most likely, someone reducing their carbohydrate intake does not equalize the remaining macronutrient content, which plummets the body into a calorie deficit which will decrease performance and may decrease hydration levels beginning a host of problems associated to performance.
An example of a study that found a carbohydrate diet to improve performance in soccer players was conducted by Souglis et al. (2013) titled, “The effect of high vs. low carbohydrate diets on distances covered in soccer.” The results claim that a high carbohydrate diet, 8g CHO kg BM outperform a low carbohydrate diet, 3g CHO by BM, in measurements of performance associated to soccer (i.e., distance covered, explosive actions). Right away the title provides ‘confirmation bias’ to anyone looking to find research that proves the heuristic that larger doses of carbohydrate are required for sustained or improved performance. However, you must zoom out and see the bigger picture when reading scientific research along with asking some difficult questions. One question is how were things controlled for that could be confounding factors, which may impact the results. For me the design of the study provides some questions. The study was a crossover design. In a nutshell, team A used the dietary intervention for period A, and then the teams played each other, then the following week the teams switched roles, team B used the dietary intervention and then the teams played again. The results showed that the team that used the high carbohydrate diet won the game. However, one must not be quick to point the finger and say, “I told you so.” Upon further examination and using the axiom; time, total and type reveals many contraindications. First off, the teams were a mixture of players from various other teams which were selected by subjective matrices determined by a hand-picked coaching staff. The timing of the study was conducted at the conclusion of the annual playing season, the end of spring. The question of motivation becomes a confounding variable. Lastly, putting a player on a low carbohydrate, restricted calorie diet at the end of a long playing season does not sound like a good idea if one is looking to determine the effects of macronutrient manipulation especially if the player has been on a moderate or high carbohydrate diet throughout the playing season.
Moreover, the historical data of the players’ dietary intake leading up to the study was not disclosed. Lastly, the authors state that calories were equated based on previous research by the same others. However, if using the standard criteria for determining calories, for every gram of carbohydrate is four calories, it is clear from the enclosed menu of food that calories were not equated. I encourage others to read the research and provide feedback to their findings.
Carbohydrate is an essential macronutrient for soccer players to perform optimally during competition and in training. However, a player can periodize their carbohydrate intake especially if exercise is not going to be as intense, heart rate above 86%, during training and gradually increase the amount taken in leading up to a competition. A player should use the offseason and the non-traditional season to experiment and see what works and what doesn’t work for them. A player can think of the energy stores, glycogen, as a fixed tank, similar to a race car. There is only so much the tank can handle. If you continue to fill a gas tank with gas when the tank is full spillage occurs and could be deadly if an open flame is present. Too much glucose can be seen in a similar frame, too much in the blood must be stored, if glycogen stores are full, muscle and liver, then the spill off can be stored to fat — not an ideal place for a soccer player.
Final thoughts, if anyone is involved with instructing or assisting an athlete with his or her diet, then a more in-depth discussion should take place and both the athlete and the person communicated the information should consider the points discussed above before just walking up and saying general comments, “you need to eat your carbs.”
1. Routledge H, Leckey J, Lee M, et al. Muscle Glycogen Utilization During an Australian Rules Football Game. Int J Sports Physiol Perform. 2019;14(1):122-124.
2. Hawley JA, Morton JP. Ramping up the signal: promoting endurance training adaptation in skeletal muscle by nutritional manipulation. Clin Exp Pharmacol Physiol. 2014;41(8):608-613.
3. Souglis A, Chryssanthopoulos C, Travlos A, et al. The effect of high vs. low carbohydrate diets on distances covered in soccer. Journal Of Strength And Conditioning Research. 2013;27(8):2235-2247. doi:doi: 10.1519/JSC.0b013e3182792147