The Importance Of Consuming Carbs During A Race
Article by Tait Hearps of Sweat Elite
We have previously released an article discussing the nuances of getting pre-race nutrition dialled in, and the pitfalls of not quite getting it right. In this article we look at some of the science behind why and how to fuel your body during the sustained effort of a race, where you need to maintain energy levels and hopefully have that extra reserve to keep up with a mid-race attack or a final burst of speed over the final strides of the race.
So, why is nutrition during a race so important? When running at reasonably high intensity, even at the aerobic pace of a marathon, most people will be in a state of metabolism where they are using a large amount of glucose for energy, as opposed to fat which can be utilised more efficiently in lower intensity exercise. Glucose is a simple sugar, which is stored in the body by condensation into the polysaccharide glycogen. Glucose levels in the blood are balanced by uptake from the gut, which results in glucose moving into the blood and subsequently into cells if it is not immediately needed for use, and breakdown of glycogen stored in cells to transfer glucose back into the blood for transport to other organs. Glycogen is predominantly stored in the liver and skeletal muscles, where most people can hold roughly 500-600g of the stuff.
Due to circulating levels of glucose and the storage capacity of the body, taking in nutrition during events shorter than an hour or so is generally accepted to be unnecessary, although interestingly Geoffry Kamworor consumed some Maurten on his way to smashing the half marathon world record (58:01) in Copenhagen earlier this year. Is this merely for publicity for the company (of which there is no shortage given it has been used by the vast majority of major marathon winners in recent years, as well as by Eliud Kipchoge in the Ineos 1:59 Challenge), or is there more to the story?
Replenishing the calories that are being burnt during exercise is clearly important to maintain consistent output, but how much do we need to be putting in? Running at a reasonably high intensity (such as the pace in a marathon or half marathon, or competing in a longer event such as an Ironman or ultra) will burn through upwards of 1000 calories per hour, which equates to roughly 250 grams of carbohydrate – or 15 bananas!
Fat oxidation will also be contributing to energy production, the proportion of energy substrate which fat supplies is inversely proportional to exercise intensity. As intensity increases more glucose is used in the place of fat, a proxy measurement for this is the respiratory exchange ratio, which is a ratio of the volume of carbon dioxide released to the amount of oxygen used during exercise. Sitting at slightly below threshold pace fat oxidation will be providing roughly 50% of substrate. However, that still means that, ignoring glycogen stores, you want to be taking in 125 grams of carbohydrate per hour just to replace what is being used. Importantly, endurance training prior to an event increases the mitochondria content in adipose tissue, essentially allowing greater energy production from fat sources over carbs. Efficacy of fat oxidation can further be enhanced through training in a fasted state. Ketogenic diets rely almost completely on fat oxidation for energy production, however we will save rabbit hole for another day. Needless to say, none of the top marathon athletes are adhering to such dietary regimes, but I digress.
125 grams of carbohydrate is a significant amount to take in whilst exercising vigorously, and most people find that this is an unattainable level. Gastrointestinal disturbances are common – nausea, bloating, flatulence – if you’re not careful you’ll be running to the toilet, not to the finish line. For a long time, conventional wisdom was that 60g/hour (or 1g/minute) of carbohydrate was the upper limit of intake that could be maintained during vigorous exercise. However updated science revealed that one way to increase carb intake, whilst mitigating the risk of GI upset, is by mixing carbohydrate sources.
Sugars make their way across the gut wall via a range of different specific transporters. The transporters can be thought of as gates that only let through their favourite sugars. If we just consume one type of these carbohydrates one type of gate will be under the pump whilst the other type is locked shut and unused. Many gels and drinks now have both fructose and glucose (as well as electrolytes and sometimes caffeine – a topic for another article). Combining these forms of carbohydrate allows multiple absorption mechanisms to occur, increasing the rate of uptake into the blood, and was also found to enhance the rate of gastric emptying: meaning that the mixture passes through the stomach more rapidly. These combined factors diminish the likelihood of bloating, nausea and diarrhoea. A ratio of 0.5-0.8g fructose:1g glucose is commonly used by sports nutrition companies.
A recent study out of Brazil found that carbohydrate intake significantly improved performance irrespective of whether participants were fed or fasted. The study is a really interesting one. Athletes were made to cycle at halfway between first and second lactate thresholds for 105 minutes followed by a 10km time trial (totalling slightly over two hours of exercise). The workout started at 9am, either 3 hours after either breakfast (which consisted of 824 calories, 67% carbohydrate), or at the end of a 15-hour overnight fast. Before exercise, after every 15 minutes of exercise and at 5 km of the TT, participants ingested 2 millilitres per kilogram of body mass of a non-caloric sweetened solution containing either carbohydrate (8% maltodextrin) or placebo (0% carbohydrate).
The results show that carbohydrate intake during the workout significantly improved endurance and performance in the time trial, rating of perceived of exertion was also lower. What is really interesting is that in the 10km time trial the fasted group who received carbohydrate in their drink (18.7 ± 0.4 minutes) outperformed the group who had breakfast and then received placebo (20.2 ± 0.8), by quite a lot… and they weren’t even that far behind the group who had consumed a carbohydrate rich breakfast and received carbohydrate in their drink (18.5 ± 0.3). Somewhat unsurprisingly the slowest group was that which were fasted and received placebo, with an average TT performance of 21.7 ± 1.4 minutes. The fact that the fasted group who received carbs outperformed the fed group who received placebo shows the importance of intra-activity nutrition. It’s all well and good to eat a good meal the night before and the day of your race and have topped up glycogen stores, but taking in nutrients during the race is crucial!
Another really interesting study in this realm is an observational study looking at nutritional behaviours of athletes in endurance events: Ironman races and marathons. The key outcomes tested were finishing time and GI disturbance, in relation to the amount of carbohydrate consumed. The basic takeaway is that “high carbohydrate intake during exercise was related to increased scores for nausea and flatulence, but also to better performance during IM races.”
Taking in lots of sugars may upset your stomach, but it will improve performance. It must be emphasised that gastrointestinal tolerance of carbohydrates during exercise is trainable, it will pay dividends to experiment with this in training and work your way up to handling greater loads of carbohydrate. The findings of this study were a statistically significant improvement in performance as carbohydrate intake increased. The data is somewhat scattered and there is definitely not a perfect correlation between carb intake and finishing time, however for this to be the case it would mean that finishing time depended only on carbohydrate intake, and not on innumerable other factors such as body size, training, talent, experience or gender, which is clearly not the case. Interestingly, a number of athletes were consuming well above 100g per hour!
Watching elites in their races you’ll frequently see them grabbing individualised mixes as they run through aid stations. This isn’t a luxury we all have access to. In most large races there will be aid stations with drink mixes available however it’s not possible to know exactly how much carbohydrate is actually in the mix (i.e. how concentrated it is). This is where gels come into play. Concentrated and small, these are easy to carry during races and can provide a large bolus of carbohydrate when it is most important.
So how much should we be taking in? The exact amount of carbohydrate we should take in during a race is dependent on a multitude of factors: duration and intensity of the run, weight of the athlete, muscle mass, gender, level of running efficiency and training, aerobic capacity and how practiced the athlete is at consuming carbohydrates during exercise etcetera, etcetera.
The American College of Sports Medicine state that “for longer events, consuming 0.7 g carbohydrates/kg body weight/h (approximately 30-60 g/h) has been shown unequivocally to extend endurance performance.” This works out at 49 grams per hour for a 70kg athlete. But what are “longer events”? And how do requirements change as the length of the event changes?
One must certainly be sceptical given the source of these recommendations, however according to the head sports nutritionist at Maurten, Tobias Christensson, the recommended amount of carbohydrate consumption is as follows:
- “Up to 1 hour of running – 40g prior to the start of the run
- 60 – 120minutes of running – 80g in total. 40g prior to the start of the run and 40g during.
- Over 2 hours – 80g/h. 80grams of carbohydrate per hour of running.”
According to Asker Jeukendrup, sport scientist at the University of Birmingham, guidelines for races can be broken up as follows:
- less than 45 min: no carbs needed
- 45-75 min: mouth rinsing, with any type of carb
- 1-2 hr: up to 30 g/hr
- 2-3 hr: up to 60g/hr
- more than 2.5 hrs: up to 90g/hr. Must be a combination of carbs that are absorbed via different mechanisms (e.g. glucose or maltodextrin combined with fructose in a 2:1 ratio)
Optimising nutrition during a race is just like optimising your race itself, it’s something that requires planning and training. The way the body will respond to carbohydrates during a race is highly individual, there’s no magic universal formula. If you are working your way up to a race where you are going to need to take on nutrition, this is something you should be preparing for, just like you’re preparing for running that distance. Start incorporating gels and sports drinks into your training, experiment with different brands and see what works for you. Have a go at titrating up the amount you are taking in and see how your body responds to it. Furthermore, consuming gels and drinks whilst running at a fast pace, and fatigued, is something that is a bit more complicated than it may at first seem, it’s definitely something you want to have a handle on prior to your big race. This could also be something you want to practice in races leading up to the main event you’re building for.
So, to summarise:
- Carbohydrate intake during races has been proven to improve performance.
- The amount one should be taking in depends on the race duration, the intensity of the run, the athlete’s size, and the athlete’s tolerance of carbohydrates during vigorous exercise.
- This is something that each individual must practice and experiment with in order to determine what works optimally for them!
We hope this has been informative for you and given you something to think about. All the best with putting it into practice!
