Carbohydrate loading, often referred to as carb loading, is a well-known and widely used nutritional strategy by endurance athletes to maximize their glycogen stores before a high-endurance event. This involves adjusting your diet and exercise levels for 1 to 3 days to boost the amount of carbs stored in your body. It may improve exercise performance, but it’s not necessary for all types of activities.
Understanding Carbohydrates and Glycogen
Carbohydrates are one of the body’s primary fuel sources. In the body, carbs are stored as glycogen, which is mostly found in the liver and muscles. During moderate to high intensity workouts, the body uses these glycogen stores as its primary energy source. However, the body can only store so much glycogen at once, and the stores become depleted throughout exercise as the energy is used to fuel it. When glycogen levels get too low, fatigue can occur.
The concept of carb-loading has been around for more than 100 years. But, despite these early observations, the importance of muscle glycogen and its relationship with exercise capacity were not confirmed until the 1960s, thanks to a group of Scandinavian researchers. They saw that this planned adjustment in diet, coupled with increased and then decreased training loads, could effectively increase the amount of glycogen stored in the muscles.
Think of your glycogen stores as the fuel you have in the tank before a long journey. The more you start with, the longer you can keep going before you need to top-up. And for reference, your body can store ~500g of glucose as glycogen in your skeletal muscles, and ~100g in your liver.
What is Carbohydrate Loading?
Carb loading is a nutritional strategy for increasing your body’s glycogen stores above the normal amount. It involves eating more carbs than usual and decreasing exercise for several days. Carb loading involves increasing the ratio of carbs and glycogen stores in your body for 1 to 3 days prior to a long or high intensity event that’s likely to deplete your glycogen stores. This may involve increasing the number of carbs you consume and lowering the amount of exercise you perform. As the name suggests, carb-loading requires ‘loading up’ on carbohydrates. But with that said, we know that some athletes who are told that “more is better” can take this advice to the extreme! Too much carbohydrate in the race build-up can be counterproductive.
Read also: The Ultimate Guide to SCD Yogurt
Benefits of Carb Loading
Experts suggest that carb loading may primarily improve performance for certain types and durations of exercise. Specifically, it may be appropriate for exercise that leads to large decreases in the amount of glycogen in your muscles. This may include high intensity endurance activities like cycling, running, or sports like soccer. In these types of exercise, fatigue can occur when glycogen levels get too low. But research suggests that carb loading may help prolong energy stores, which means you can have energy for longer periods and delay fatigue. Research has shown that carb loading effectively can prolong exercise capacity by up to 20%, and has improved time trial performance by 2-3% when taking part in high intensity events >60mins.
An older 1997 study found that carb loading improved performance by 2% to 3% for exercise lasting more than 90 minutes. Carb loading may be beneficial for longer periods of high intensity exercise. But it’s unlikely to be effective for shorter durations of exercise or lower intensity exercises, such as weight training. This is because fat is the primary fuel source for these types of workouts.
Who Should Carb Load?
Carb loading is great for endurance athletes, like marathon runners, cyclists, and triathletes, who are gearing up for events that last longer than 90 minutes or for athletes with multiple events in one day. However, any sport that requires high intensity, no matter how long, may require an increased carbohydrate intake to ensure an athlete has adequate fuel stores.
Endurance athletes require a lot of sustained hard exercise efforts, and carb loading helps to saturate their muscles with glycogen, giving them the fuel to keep going. If you’re working with an endurance athlete, carb loading can give them that extra energy boost and edge needed to perform their best.
How to Carb Load
In general, experts recommend consuming around 10 grams (g) per kilogram (kg) of body weight (4.5 g per pound) of carbohydrates per day. So, if you weigh 70 kg (154 pounds), that equals 700 g of carbs per day. Some experts previously used a percentage ratio, where 60% to 70% of the total calories were from carbohydrates. But this is no longer used, as caloric strategies range widely from person to person. It’s important to note that while you may increase the amount of carbs in your diet, you’re not increasing the total amount of calories. When you increase the number of carbs, you will decrease proteins and fats, too.
Read also: Understanding Keto and Carb Loading
The usual advice is to increase your carb intake to ~8-12 grams per kilogram of body mass to fully replenish your muscle glycogen stores.
To get the recommended amount of carbs, you should focus on foods that are high in carbs, low in fat, and don’t have too much fiber. It’s important to continue eating protein and healthy fats to help support your muscles. Try to focus on lean protein sources, such as fish, lean cuts of meat or poultry, and low fat dairy. What’s more, eat foods you enjoy and that are familiar to you.
Classic 6-day Method
There are several different types of carb loading, but all strategies involve increasing the number of carbs you eat and temporarily decreasing the amount you exercise. The classic 6-day carb load strategy was first developed in the 1960s. It’s designed to completely deplete glycogen stores during the first 3 days, then eat high amounts of carbs over the next 3 days to saturate the stores.
- Days 1 to 3: A low carb diet, where 5% to 15% or 100 g of your calories come from carbs, is combined with high intensity exercise.
- Days 4 to 6: A high carb diet, where more than 70% or 500 g of daily calories come from carbs, is combined with low intensity exercise.
Although experts once believed the initial “depletion” phase helped the body produce more glycogen once carbs were eaten again, research from 2017 shows it may not be necessary.
Classic 2- to 3-day Method
Healthcare professionals now recommend a carb loading phase of 36 to 48 hours before the high intensity event. The number of carbs this typically involves consuming is 10 to 12 g per kg (4.5 to 5.5 g per pound) of body weight. Some people also consume a low residue diet for 3 days before the high intensity event to help limit possible gastrointestinal symptoms. This diet limits high fiber foods that may be hard to digest and leave “residue” in your digestive tract after early digestion stages.
Read also: The Hoxsey Diet
It is quite simple. The week before your race as your mileage tapers, keep your nutrition fairly similar to if you were running a higher mileage week. This will slowly begin the carb load. Then, we take a strategic approach 2 - 3 days out from the race. Research shows adequate carbohydrates to fully load glycogen stores are 10 - 12 gm/kg x 2 days or 8 gm/kg x 3 days.
Common Mistakes to Avoid
Before you start a carb loading program, there are several common mistakes you should be aware of.
Carb Loading When You Don’t Need To
Research suggests that carb loading may be beneficial for people getting ready to perform a high intensity activity that lasts longer than 60 minutes, such as a running or cycling race. When it comes to shorter durations and intensities of exercise, carb loading may not provide any benefits. For instance, a 2022 review found that carb loading is most likely not beneficial for weight lifting, unless lifting at high volumes. This means performing more than 10 sets per muscle group in one session. Consider the type of activity you’re doing and whether carb loading may be beneficial. If you’re unsure, speak with a registered dietitian, athletic coach, or healthcare professional. They can help you decide the pros and cons of carb loading for you.
This strategy may not be useful for you if you are recreationally active but not an athlete or competitor in long-duration events.
Eating the Wrong Amount of Carbs
Not getting enough carbs during an intended carb loading phase may affect your performance on the event day, while eating too many carbs may lead to eating too many calories, unintended weight gain, or a change in your diet. To determine how many carbs to eat during a carb loading phase, start by calculating your daily carb intake by recording all the food you eat for several days using a food-tracking app or the nutrition labels on your food. Then you can divide the grams of carbs you eat each day by your weight to compare your current intake to carb loading recommendations.
For example, if you weigh 70 kg (154 pounds) and you normally eat 300 g of carbs per day, then you’re consuming 4.2 g per kg (1.9 g per pound) of carbs per day. Experts recommend eating around 10 g of carbs per kg (4.5 g per pound) of body weight per day during a carb loading phase. Based on these recommendations, you would need to eat more than double the amount of carbs you would normally.
The most common reason carb loading doesn’t work is because we don’t eat enough carbs.
Eating Too Much Fat
Fat is an important macronutrient in a balanced diet. While more research is needed to understand the role of fat in carb loading, it may be beneficial to limit the amount you eat to avoid eating too many calories and feeling sluggish. That said, a 2022 study found that eating a high fat meal after a carb loading phase 3.5 hours before the planned event may actually help improve glycogen stores during the event. A registered dietitian could help you determine how much fat you should eat during your carb loading phase.
You don't want too much fibre protein or fat in your carb loading meal ideas. In regular everyday life to support a healthy athlete, these are crucial for a balanced diet!
Eating Too Much Fiber
Some people report that eating high fiber foods during a carb loading phase may increase the risk of experiencing gastrointestinal symptoms like stomach discomfort, bloating, and water retention during the sporting event. Carb loading is a unique time when it may be better to choose refined grains like white bread or pasta over whole wheat.
Choose lower fiber foods.
Exercising Too Much
Lastly, failing to decrease or “taper” the amount of exercise you perform during carb loading could limit the extent to which your glycogen stores increase during your high carb diet. A personal trainer or registered dietitian could help you determine the best type, duration, and intensity of exercise to perform during a carb loading phase.
Not Practicing
Some athletes won’t practice carb loading in training and then try to overload on carbs the night before rather than gradually increase their intake over several days. This type of over-fueling can set the stage for GI distress, impairing performance. It's a good idea to practice your carb loading meal plan before the race. The switch to a low fibre, high carb diet can cause stomach issues for some people. Give yourself time to find out what the best foods are for you. You only want to be eating familiar foods on the run up to the race, because you don't want any unforeseen digestive issues to spring up!
Food Choices During Carb Loading
Use carbohydrate foods you are familiar eating. Focus on high carbohydrate foods, not high fat foods.
To get the recommended amount of carbs, you should focus on foods that are high in carbs, low in fat, and don’t have too much fiber. The table below highlights some foods to consider eating and limiting during your carb loading phase:
It’s important to continue eating protein and healthy fats to help support your muscles. Try to focus on lean protein sources, such as fish, lean cuts of meat or poultry, and low fat dairy. What’s more, eat foods you enjoy and that are familiar to you.
Lower-fiber carb options like bagels, juices, muffins, white rice, potato, and white pasta, as they decrease the risk of digestive issues during the event. Non-starchy vegetables are not needed while an athlete is carb-loading, as they can displace carbohydrate intake and contribute to additional gut residue. However, fruit is usually well tolerated as long as it is low-fiber. Examples of low-fiber fruit include bananas, applesauce, and fruit juices.
Sweets like gummy bears, fruit juices and certain sports drinks can be excellent sources of simple to digest carbohydrates during a carb loading phase, as they contain a concentrated amount of carbs but aren't heavy. A great carb loading snack!
Hydration
As we increase carbohydrates, we also want to increase fluid intake. Lastly, each gram of glycogen is stored with at least 3 grams of water, which can make weight gain a noticeable response to glycogen supercompensation in many athletes.
Sample Carb-Loading Meal Plan
The following is a sample carb-loading meal plan for optimizing energy levels and performance:
- Day Before the Event
- Breakfast: Bagel with cream cheese or nut butter, scrambled eggs and fruit, or oatmeal with fruit and milk
- Mid-morning Snack: Low-fat Greek yogurt with maple syrup and fruit
- Lunch: Pasta with tomato sauce or pesto with a lean protein like chicken or salmon
- Afternoon Snack: Fruit smoothie or dates with pretzels
- Dinner: White rice with a lean protein source
- Evening Snack: Low-fat chocolate milk with a banana
- Day of the Event
- Pre-event meal (1-4 hours before): 1-4 grams of carbs per kilogram of body weight (e.g., 2 g/kg two hours before)
- Consider a carbohydrate gel, sports drink, or banana right after warming up
- During events lasting one to two hours: 60 grams of carbohydrates per hour
- For events lasting longer than two hours: 90 grams of carbohydrates per hour
- Post-Event
- 1 to 1.5 grams of carbohydrates per kilogram of body weight
- 0.4 grams of protein per kilogram of body weight
- Replace fluid lost with electrolyte-enhanced beverages
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