There is nothing more frustrating than putting in all the time and training for a big event and you come up short because of nutrition problems. I have had my fair share of upset due to stomach issues, or by not keeping up on energy needs during races. Other athletes outside of the endurance realm also experience these type of issues, so this can apply to more sports than strictly endurance sports. What is the key then to increasing your carbohydrate intake during exercise while not upsetting your stomach? Let's get into it.
Why are carbohydrates ideal during exercise? Carbohydrates metabolize quickest compared to fat and protein and require less oxygen to do so, meaning when you're pushing hard, you can rely on carbohydrates to work fast and efficiently to keep your muscles and brain working optimally. Carbohydrates are also easier to digest during exercise which will reduce the chances of getting sick in the middle of an event. Trust me when I say you can most definitely still get sick. The type and quantity of carbohydrate can make or break your day. Too much, you can be sure you'll be taking some pit stops, too little at you won't perform to your potential.
Stored carbohydrates only go so far. A convenient evolutionary trait allows our liver, muscles, and even brain to store carbohydrates for later use. This is called glycogen and we can store enough carbohydrates to push for roughly two hours before glycogen is depleted at which point we are in need of consuming more carbohydrate. When those two hours are up and we don't consume carbohydrates, performance will inevitably begin to fall due to a decrease in ATP (available rapid energy) leading to reduced muscle contraction. Although you can't prevent glycogen decreasing even while eating as much carbohydrates as possible during exercise that is at 60% of Vo2max (moderate intensity), you can prevent complete glycogen depletion. That being said, the more carbohydrates you can get into your body during exercise, the more likely you are to maintain the energy needed for high output for as long as you need.
Is there a way to increase the amount of glycogen you can store? Remember, glycogen is the amount of carbohydrate your body can store in muscle, liver, and brain cells. First, exercising on a regular basis can improve your ability to store more carbohydrate. The more often you deplete glycogen, your body improves it's ability to increase glycogen capacity. Second, by drastically reducing carbohydrate consumption over several days while exercising, you completely drain your glycogen which then causes a super compensation effect when you do eat carbohydrates again. Seeing the reduction in carbohydrates, and likely overall energy consumption before an event can make you fatigued and cause workouts to suffer, I don't think the second method is worth the risk.
Carb loading is a great way to top off your glycogen stores before a big event. I like to recommend athletes start doing this 5-7 days out from a big event so they can gradually increase rather than stuffing it all in the day before. This way your belly isn't irritated the morning of your event. I find most people overdo it the night before and jeopardize their performance because of it. Again, an advantage for sure, but the risk of feeling sick and overdoing it just to make sure you have completely topped off your glycogen could be a mistake.
What is the best way to ingest carbohydrates during exercise? There are two carbohydrate molecules that have proven to be most effective which are glucose and fructose. However, consuming them alone isn't nearly as effective as consuming them together. In fact, one study discovered that at 50% Vo2max, 1.1 grams of carbohydrates consumed per minute seemed to be the maximum threshold when using glucose alone, whereas combined with fructose the threshold was 1.75 grams per minute. Over an hour that equates to 66 grams using just glucose versus 105 grams using both fructose and glucose. That's a huge difference. How? Glucose and fructose use different metabolic pathways so instead of exhausting one transport pathway, SGLT1 in the case of glucose, or GLUT5 in the case of fructose, you can utilize both pathways to get more carbohydrates into the cell and into the bloodstream. Combining the two has also been shown to reduce gastric distress. To optimize the absorption of these two molecules together a 1:1 or up to a 2:1 ratio of glucose to fructose is recommended.
In conclusion, look for products that contain roughly a 1:1 to 2:1 ratio of glucose to fructose to maximize carbohydrate absorption and to reduce chances of stomach issues. This goes for not only endurance athletes, but high intensity athletes as well. Try to avoid products that contain just fructose or glucose. Maltodextrin is the most common ingredient in sports products which is effective, but without fructose may not benefit you as much. Table sugar is sucrose which is 50% glucose and 50% fructose making is a great and simple option. Don't stress too much about glycogen leading up to an event as the risks can often outweigh the benefits. Eat more carbohydrates going into an event but don't obsess about getting absurdly full the day before. Test out how many carbohydrates you can handle during longer days and keep track of what you consume per hour. Try to be as consistent as possible eating every 30 minutes. The upper limit is different for everyone but a minimum of 60 grams per hour should be tolerable.
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