It’s not a new concept. It’s the all too familiar pasta party dinner before an event. As a kid, I can remember having pasta get-togethers before most swim meets and soccer tournaments. In college, it was a guaranteed pasta and red sauce with dinner rolls every night at championship meets. I ended up eating this spaghetti dinner so many times that I avoided it for several years afterwards. It’s true. Carbohydrates can improve exercise performance. The single pasta dinner may have worked for those events, but what’s best for competing in endurance events where you’re potentially racing for hours to days? These events require a bit more carb preparation.

What is Carb Loading?

Glucose is one of the primary fuel sources, and is the preferred fuel source for moderate to high intensity exercise. Carbohydrates in the diet are digested into simple sugars: glucose, fructose, and galactose. These sugars are sent to the liver, where fructose and galactose are converted into glucose, and then sent out into circulation. In periods of higher carb consumption, excess glucose is stored in the liver and muscle as glycogen. As circulating blood sugar levels drop, (i.e., you’ve gone several hours since your last meal) the glycogen in the liver is converted back to glucose and sent out into circulation. However, glycogen stored in the muscles can only be used by muscle and will not re-enter circulation in the bloodstream. Once the glycogen is there, its fate is to be used by the muscle.

By eating large quantities of carbohydrate, athletes can stuff their muscle to hold more glycogen. This means that there’s a readily available fuel source for muscles for exercise, already where it needs to be. With more fuel readily available, athletes can improve exercise performance in events lasting over 90 minutes and delay fatigue as carb loading extends the time until glycogen stores are fully depleted.

What happens when athletes run out of glucose? Fully depleting glycogen stores is what’s known in endurance sports as “hitting the wall” or “bonking”. Anyone who’s experienced it knows how unpleasant it feels. Unfortunately, it seems to get highlighted when athletes are struggling, losing control of their bodies, and crawl across the finish line. Instead of seeing an athlete in distress, many will see an under fueled athlete as inspirational. The muscles no longer have the energy they require to function properly. This results in sudden fatigue, muscle cramping, mental fog, reduced exercise capacity, and low blood sugar levels.

Generally, athletes can begin carb loading 24-72 hours in advance, but many different loading strategies could potentially be used. Athletes should aim to consume 8-12g carb per kilogram bodyweight per day. Initially it was believed that glycogen stores had to be fully depleted before a loading protocol could begin. This method has since been disproven. Once the glycogen is in the muscle, it’s not going anywhere until its used by the muscle. So, the combination of increasing carb intake in the days leading up to a race and lessening exercise (i.e., tapering) seems to be a good combination.

Women and Carb Loading

As with most research, we have significantly more data of the effects of carb loading and athletic performance in men than we do in women. However, it seems that female athletes can load carbohydrate stores at comparable levels to men when loading protocols are done appropriately. The effectiveness of carb loading in females seems to be dependent on the amount of carb ingested, the total energy (calorie) intake, and phase of the menstrual cycle in premenopausal women.

Women should aim to ingest 8-10g/kg carbohydrate in order to effectively load stores. For a 60kg (132lb) women, this is roughly 480-600 grams of carb per day. Since every gram of carb has four calories, this equates to 1920-2400 calories exclusively from carbohydrates. This doesn’t account for that fact that most foods offer a mix of nutrients (protein, fat, and carbohydrates) not just carbohydrates, alone. This poses a difficult challenge for female athletes trying not to greatly overconsume calories while also tapering off exercise. Overeating calories may sound undesirable to some athletes. But in order to carb load effectively, some female athletes may need to overconsume their total energy intake by as much as 30% to achieve glycogen supercompensation.

Another factor affecting muscle glycogen storage in premenopausal women seems to be the phase of their menstrual cycle. Women have a greater capacity for storing muscle glycogen during the luteal phase compared to the follicular phase. However, this is an area that requires more research before more specific menstrual cycle recommendations can be made.

Downsides to Carb Loading

It's not all rainbows and gummi candies during a carb load. Athletes may not feel that all carbohydrate loading strategies are well tolerated. Additionally, every gram of carbohydrate stored will store three to four grams of water along with it. For this reason, if you’re carb loading effectively, you should expect the scale to increase in the days leading into the race. Athletes should practice and choose a loading plan to minimize GI discomfort. Despite the negative feelings, carb loading is still beneficial to performance so it’s important to practice carb loading strategies prior to race day to figure out what works best.

Common Carb Loading Mistakes

I think where I most commonly see athletes go wrong in a carb load is using it as a free pass to eat whatever they want. Don’t get me wrong, pizza, donuts, and ice cream are all delicious sources of carbs, but they’re also probably too high in fat to be fully relied upon as carb loading foods. High fat foods become a problem for two reasons, one: total calorie intake becomes much higher than necessary (or desired) and two: fat induces satiety, so athletes may start to feel full before consuming enough carbohydrate to super compensate glycogen stores.

Athletes should choose foods that provide high amounts of carbohydrate, but minimal fat and fiber. Moderate amounts of protein are ok, but again, protein induces satiety so consuming high amounts can make you feel too full to eat enough. Instead of a food like potato chips, choose pretzels, or baked potato (without skin). Athletes should choose foods that are familiar. The saying, “nothing new on race day” holds true for the 24-48 hours leading into an event as well. Examples of high carb meals include pancakes with syrup, low-fiber cereal with banana, rice bowls, vermicelli noodle dishes, or pasta. Avoid alcohol and spicy food. As much as those foods can be fun going in, they can be very unpleasant going out, so they are best left until the race is over.

For those athletes who find it difficult to eat enough food, I suggest leaning into simple sources of carbohydrates or liquid carbs. This can be especially helpful in the final 24 hours leading into a race. Sugar-based candies such as jellybeans, Swedish fish, gummi bears, or dots all provide simple sugars and contain little to no protein or fat which make for good snacks between meals. Liquids like fruit juices (with or without added sugars), sports drinks, and soda also offer primarily carbs and may be easier to get down than foods. Many of these processed foods don’t offer much in terms of vitamins, minerals, or other important nutrients for health. But a few days of high intake aren’t going to derail your health and may help athletes achieve the high carb intakes they’re looking for.

Adequate training, hydration, and day-to-day nutrition all play a crucial role in race performance. Like everything else, practicing fueling, and carb loading are key. It’s important to remember that carb loading is just one piece of preparing for race day and does not reduce the need for stellar intra-race fueling plans. The better you can take in adequate fuel, the more likely you’ll have a positive race experience.