Is Carbohydrate Loading Essential For Optimal Endurance?

Research in the field of nutrition and how it relates to athletic performance has come a long way in the past 30 years. Discoveries have been made regarding which foods and supplements result in better training and optimum performance. These discoveries have especially been useful in endurance sports, where nutrition is a key factor in how well an athlete can perform.

Unfortunately, like many topics in the field of health and fitness, endurance sports is also riddled with misinterpretations and myths, one of the most common ones being that Carbohydrate loading (or “carbo-loading”) is required for optimizing an athlete’s endurance.

What Exactly is Carb-Loading?

Carb-loading refers to a 6 day period prior to a big endurance sporting event such as a marathon where for the first three days, the athlete goes on a very low-carb diet where the glycogen reserves are almost totally emptied. Then for the next three days, the athlete literally loads up on carbohydrates in order to maximize glycogen reserves in the muscles for better performance and optimal endurance.

The reasoning behind the latter stage of the process is that by filling up the body with more and more carbohydrates and maximizing the glycogen reserves, the athlete has to rely less on stored fat for energy, which is a good thing because stored fat is not a good source of energy and it’s one of the main reasons that athletes reach the point of total exhaustion. Carbohydrates are a good source of energy and it’s much better to rely on them for energy during a sporting event.

The reasoning behind the first part of the process where the athlete depletes the glycogen reserves, is that by loading up on carbohydrates after a period of carbohydrate-depletion, the athlete’s body makes up for the lost glycogen by storing even more glycogen in the muscles than usual, which gets the athlete in prime condition for an endurance sporting event. This might make you believe that carbo-loading is a rational approach to preparing an athlete for a sporting event, but new scientific studies are showing that it may not be.

Why Carbo-Loading Does Not Work

The main reason carbo-loading does not work is that the average human body can only store about 500 grams of glycogen. In a typical marathon, the average runner burns about 5000 calories. Suppose an athlete has maxed out their glycogen reserves at 500 grams. This means that the athlete will still burn off about 3000 calories of fat before finishing the marathon (500 grams = 2000 calories), which means reliance on stored fat for energy is ultimately unavoidable.

The glycogen-depletion that the athlete goes through a few days earlier can also severely hamper performance. Also, many athletes have reported feeling bloated as a result of carbo-loading – this can also have a negative effect on an athlete’s performance.


Research has shown that the best way to prepare for a sporting event in terms of nutrition is to simply have a well balanced diet. It is ok to consume more carbohydrates than usual to prepare, but it is best to not load up on them.

According to doctors and nutritionists, what an athlete consumes during an endurance sporting event is much more important then what the athlete consumes days or even hours prior to the event. Sports drinks such as Gatorade do a great job of replacing glycogen lost during a race and are a much safer alternative than carbohydrate loading.


About Rob May

Rob is a freelance writer who used to struggle with belly fat and love handles and tried many diets and weight loss programs. He was eventually able to get rid of them through rigorous exercise and a strict diet. He recently started his own site about losing love handles in hopes of helping others who are struggling to lose belly fat.


  1. Katie Kristy says:

    I am a marathon runner and I mainly focus on adding more protein to my diet and I tend to make sure that I basically have a well balanced diet everyday. I make sure my balanced diet is the same before and after the race. I may drink more water before the race, but other than that, it is the same.

  2. Ben Steller says:

    Many say that you need to pack yourself with so much carbo before a race, but I say you should not overload yourself with that. The body is made to get balance of nutrition. Do not overload your body with something that it is not used to taking such an overwhelming amount.

  3. I’ll be participating in an indoor marathon and I was hoping to get some information on carbohydrate loading. I was pretty much sold on carb-loading until I came across this article. The thing is if we can only store about 500 grams of glycogen, then it’s pretty pointless to try to discuss this any further. This is why you need to look at the facts and not the hype.

  4. I can’t believe that there are athletes out there that would actually believe that carb loading was a good idea. If your fast all day and then before your activity you load up on carbs for energy you are likely to make yourself sick. Maybe having slow carbs in your body all day would be the best idea and then try something simple like a banana before.

  5. Carb loading to me would be very scary where is your body going to store all the glucose when it is broken down? I am not saying that isn’t the right thing to do for some people but you have to have a certain body chemistry in order for this to do you any good what so ever. You have a lot of good advice but make sure you know your body style first.

  6. I had heard of athletes doing this before a game like you mentioned but I never did believe that was a true thing. Carb loading to me is never a good idea but that is because I found out that is what causes me to gain weight. I figured that out because I went on a low carb diet and lost weight when nothing else would work.

  7. It is very interesting to me that there are such contradicting article on weight loss, don’t eat carbs, eat slow carbs, follow a low carb diet, carb load before a work out etc. what is the average person supposed to believe? If you want to make a change in your life and get healthy and fit you have to have a degree in nutrition so you know what is good and what isn’t.

  8. When I was in track in high school I was as printer and a relay runner and for energy during the meet we would eat dry jello, you lick your finger and dip it in the jello and eat it. I don’t know if it actually did anything for us but we thought it did so mentally we were ready to race, maybe this is a mental thing, they think it really works.

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