Cycling Nutrition: The Basics – Glucose, Glycogen and Carbohydrates

While proper nutrition is one of the most important factors affecting long-distance cycling on a day-in, day-out basis, there is so much misinformation out there that knowing what to eat and when to eat it can be Burning glucosedifficult.  Part of the reason for this is that it’s early days yet for nutrition science; much remains to be learned and nutritional theories are often revised as new information becomes available.  Another reason is that the subject of sports nutrition is confused in the minds of many with the subject of dieting.  Unfortunately, dieting in the US is a multimillion dollar industry that is fat with fads and outright foolishness.  Finally, many cyclists seem to have a deep emotional commitment to their cycling-related eating habits and resist change.  In these Cycling Nutrition posts I’ll try to present nutritional information that is based on research found in peer-reviewed scientific journals on nutrition and cycling and endurance sports in general.  In this post we look at the basics of how muscles are fueled that underlie every discussion of nutrition for cyclists. In other posts we examine eating during a ride, eating after the ride, and bonking.

Muscles burn glucose for energy.  The longer you ride or the faster you ride, the more glucose your muscles need for fuel.  When you get on the bike and start pedaling, the demand for glucose for your leg muscles increases and a signal goes out to the body to start supplying the glucose you need.

Glycogen and glucose

Where does the glucose come from?  The body doesn’t store raw glucose.  Instead, it makes glucose from other substances.  Glucose can be derived from breaking down stored fat and protein.  Subcutaneous fat (the excess fat stored under the skin) is an especially good energy source because fat contains roughly twice the number of calories as either protein or carbohydrate.  This means you get more fuel in the form of blood glucose from breaking down a gram of fat than from a gram of either protein or carbohydrate.  Indeed, breaking down stored fat to increase the level of blood glucose is the reason why exercise leads to weight loss.  The problem with relying on breaking down fat to produce glucose is that the process is relatively slow and energy intensive.  Metabolizing (breaking down) fat can be a useful long term source of energy but it is too slow and inefficient to support immediate and short term demands for glucose to fuel ongoing athletic activity.

In order to have fast access to glucose when needed, excess glucose in the blood is stored in a form known as glycogen.  Glycogen can be quickly broken down to supply glucose as needed.  The main storage locations for glycogen in the body are the muscles and the liver.  Liver glycogen is volatile in the sense that it doesn’t last long.  This is because liver glycogen serves as an energy source for the entire body.  When liver glycogen is metabolized the glucose that is produced enters the blood stream and can be used any place in the body where it’s needed.  If you go to bed with with liver glycogen stored at maximum capacity, a large proportion of it will be gone when when you wake up because it was used to fuel the body’s needs while you slept.

Muscle glycogen is more stable in the sense that once stored it remains in place much longer.  This is because muscle glycogen does not enter the bloodstream.  The glycogen stored in an individual muscle can only provide glucose for that muscle.

So, you’re pedaling along burning glucose derived from glycogen stored in your liver and your cycling muscles and everything’s just peachy.  Until you run out of stored glycogen.  The body can store enough glycogen to support approximately 90 minutes of moderate intensity exercise.  What happens when that glycogen is used up?  Where do your muscles get the glucose they need to keep working?  Some of it can come from fat that has been slowly breaking down while you’ve been riding but that won’t be enough to supply your needs.  Once you’ve exhausted your glycogen stores, most of the glucose you need is going to come from what you’ve been eating and drinking during the ride.  This is where carbohydrates enter the picture.

Basic nutrition for any endurance sport such as cycling is primarily about carbohydrates for the simple reason that carbs can be broken down to supply glucose much more quickly and efficiently than either fats or proteans.  While you’re on the bike you need a steady supply of carbs to both fuel ongoing activity and stretch the time before your stored glycogen is completely exhausted.  When you’re off the bike you need carbs to replace the glycogen you burned during the ride you just finished.  For anyone engaged in an athletic activity that lasts for 90 minutes or more, carbs are what basic nutrition is all about.

 

 

13 thoughts on “Cycling Nutrition: The Basics – Glucose, Glycogen and Carbohydrates

  1. Pingback: Cycling Nutrition: Eating on the Bike « Tuned In To Cycling

  2. Pingback: Cycling Nutrition: The Bonk « Tuned In To Cycling

  3. Pingback: Cycling Nutrition: Eating After the Ride « Tuned In To Cycling

  4. I’m a type 2 diabetic. During the ride I do gatorade, gu, clif bars, etc. I’ve always thought that as long as I’m excercising that consuming all those carbs is okay. True? What about after the ride? I know riders are supposed to consume more carbs in the 30 minutes after but I am concerned that that will push my sugars too high.

  5. The short answer here is that I am not competent to answer your questions; you need to bring these concerns to a doctor who knows the specific details of your diabetic condition and who also knows about athletic nutrition.

    With that said, you’re asking exactly the right questions. For readers who may not be well informed about diabetes, type 2 diabetes is a metabolic malfunction whereby insulin is either in short supply, does not function as effectively as it should, or both. Insulin is an essential component (in most circumstances) in the processing of blood glucose. Type 2 diabetics are subject to abnormally high levels of blood glucose because their insulin cannot process it effectively.

    On the one hand, athletes need carbs to supply glucose to provide fuel for working muscles. On the other hand, the type 2 diabetic does not process glucose effectively. A way has to be found to balance the need for glucose to support athletic activity and the reduced ability of the system to process glucose effectively. That balance will depend on the specifics of the individual’s diabetic condition.

    A complicating factor for the type 2 diabetic is that the body will process blood glucose into glycogen that can be stored in the muscles and liver in a highly efficient and effective manner during a 30 to 60 minute period after long or intense exercise. For more details about this, see our post on Eating After the Ride. One of the main reasons why this short window of glucose-to-glycogen conversion is so efficient is that it does not use insulin. While this means that the type 2 diabetic may be able to take full advantage of this process, he or she may also find themselves hammered with blood glucose levels that they cannot handle when the high-efficiency conversion process turns off.

    An important factor for cyclists to keep in mind, especially if you are a diabetic, is that eating a lot of carbs to flood the system with glucose in the 30 minutes after exercise is only necessary if you are going to engage in prolonged or intense cycling the next day. If you are taking the next day off or are going to be doing light riding for about an hour, there’s no real need to restock glycogen supplies. Normal, healthy eating patterns will typically replenish muscle glycogen effectively if long (90 minutes or more) or intense riding is separated by two days or more.

  6. Will I still lose fat around the abdoman if I eat Carbs during and after a 90 minute ride?
    I am riding to lose weight. But your information makes sense.
    Does a rider burn both fat and carbs if carbs are ingested during the ride?

    • Although the multi-billion dollar fad diet and weight loss industry would like it if you would believe otherwise, the simple fact of the matter is that in the absence of illness or a malfunctioning metabolic system if you burn more calories than you take in you will lose weight and if you don’t, you won’t. Cycling burns calories and the harder and longer you ride, the more calories you’ll burn. Whether or not you lose weight depends on how many calories you take in to offset the calories you burned riding.

      I’m a pretty good example of this. My initial motivation for getting on the bike was to lose weight and get back in shape. I enjoyed riding so much that I had forgotten these motivations and was riding for pure enjoyment after about 10 minutes. The end result was that I lost 60 lbs and could eat as much as I wanted of anything I wanted because I burned it all off on the bike.

      If you burn more calories during the ride than you take in while you are riding, you will burn both stored fat and stored glycogen to fuel the ride. The system will give preference to burning stored glycogen because it can be converted into glucose (which is what fuels the muscles) more quickly and more efficiently. Getting glucose from fat is a slow and inefficient process.

      A common mistake is to avoid eating during or after a ride based on the idea that if you don’t take in any calories from food, all of the calories burned to fuel the exercise will come from stored reserves (such as body fat) and you will lose more weight. The problem with this reasoning is that getting energy from stored fat is too slow and inefficient to fuel intense, ongoing activity. Without an adequate fuel supply the intensity of the exercise will drop and you end up burning many fewer calories during the time spent exercising. The harder you go, the more calories you burn, and the more calories you burn, the greater the potential for weight loss. You need a ready supply of energy to fuel intense exercise and carbs are the best source for this.

      The nutrition posts here on Tuned In To Cycling have focused on providing energy to the muscles in the form of glucose.However, there’s a lot more going on in the body during and after exercise, especially intense exercise. For example, exercise breaks down muscle tissue and the system works to rebuild that tissue when the exercise stops (this is why exercise makes us stronger). Energy is needed for that rebuilding process and it mainly comes from macronutrients, especially fats, that are stored in the body. If your caloric intake after exercise is less than the calories burned during exercise, you will reduce body fat.

      Take a look at our post Eating After the Ride Part 2 for some interesting and useful information about the consequences of replacing calories burned during exercise with fats, carbs or both during a 10 hour period after exercise. The post summarizes a well-done study published in the Journal of Applied Physiology. The most interesting finding reported in the study for riders interested in losing weight was that fat metabolism the day after exercise took place was elevated in riders that replaced the glycogen burned during exercise with carbs but did not replace the fats burned during exercise with fats. In other words, making sure you replace glycogen with carbs while avoiding fats after exercise results in higher-than-normal breakdown of body fat while stocking your system with sufficient glycogen to fuel exercise on the following day.

  7. Pingback: Dehydration and Over Hydration (Hyponatremia) for the Cyclist « Tuned In To Cycling

  8. Pingback: Cycling Nutrition: The Value of the Glycemic Index for Cyclists | Tuned In To Cycling

  9. Hi! I know this is kinda off topic but I was wondering if you knew where I could find a captcha plugin for my comment form?
    I’m using the same blog platform as yours and I’m having problems finding one?
    Thanks a lot!

  10. There is a book I like, called “Racing Weight – How to get Lean for Peak Performance”. In the book they recommend doing one “fasting workout” per week – a long, moderate intensity workout without having a meal beforehand and without carb consumption on the bike. The idea is that one would burn more fat this way and boost general fat-burning capacity (paraphrase). What are your thoughts on this suggestion? I’m planning to do this on my next base aerobic ride, but after reading this article I am having second thoughts…Thanks! :)

    • I am not familiar with the science (if there is any) behind the claims about exercising without carbohydrates in order to boost fat burning. It sounds like it may be based on the “fat burning zone” business but I may be mistaken about that. The fat burning zone is a real phenomenon but as a weight loss method it’s targeted at people who forgot what they learned in grade school about what a percentage is. There will be an upcoming post in the Cycling and Weight Loss series on the fat burning zone.

      Personally, I would be very reluctant to follow any procedure that would result in not having enough glucose in the system to fuel the ride. Take a look at the recent post on Riding the Bike to Lose Weight. If I wanted to lose weight on the bike I’d focus on how to burn more calories, not on how to ingest fewer calories while I’m riding.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s