Cycling Nutrition: The Value of the Glycemic Index for Cyclists

idiots guide

Information about the glycemic index and many other topics can be found in Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride which can be purchased on  For information about the book and how it relates to what I’ve posted to Tuned In To Cycling, please check out this post.

The diet industry is big business; in the US it is estimated that people spend in the neighborhood of $35 billion dollars a year on diet-related products.  (To make that number more comprehensible, if you make $50,000 a year Americans spend your yearly salary on diet products approximately every 80 seconds.  24, 7, 365.)  A large part of this industry relies on consumer ignorance and gullibility to enable the promotion and sale of one fad diet idea after another.  One of the ideas heavily promoted in the diet industry is the glycemic index.

Is the glycemic index useful? Yes.  Is it all the diet industry makes it out to be?  Not even close.  For our purposes here, is it useful to cyclists?  I think the best answer here is – marginally.

First of all, what is it?  The glycemic index is an indicator of how long it takes food to be converted to glucose in the blood.  Glucose is the fuel that muscles burn when they are working and on-the-bike cycling nutrition and performance is largely about glucose production and consumption.  Having an idea of how long it will take to get the food you eat while you ride converted into blood glucose has the potential to be very useful.

Will the glycemic index tell you how long it takes for the Powerbar or raisins you ate to be converted to blood glucose in seconds, minutes and hours?  No.  The glycemic index compares the time it takes for a particular food to be converted to glucose in the blood to the time it takes for pure glucose ingested orally to appear as glucose in the blood.  Glucose is arbitrarily assigned a glycemic index value of 100 to serve as a basis for comparison.  Particular foods are then given a glycemic index value, typically less than 100, based on how long they take to be converted to blood glucose in comparison to pure glucose.  A high glycemic index indicates a food is rapidly converted to blood glucose; a low glycemic index value means it takes a relatively longer time for that food to be converted to blood glucose.  The glycemic index doesn’t tell you how long it takes to get blood glucose out of food, it gives you a rough idea which foods are converted to blood glucose more quickly than others.

eating on bikeThis sounds like it should be of great use to the cyclist.  You’re burning glucose constantly on the bike, you need more, you’re eating to get more, the glycemic index will tell you what to eat to get that glucose as quickly as possible.

It’s all good, right? Not really. Why not?

The glycemic index of most food varies with so many factors that the rough idea the glycemic index gives you of which foods are converted into blood glucose faster can be very rough indeed.  Here are some examples.

  1. For many foods, glycemic index varies as a function of how the food was prepared (pasta boiled for 10 minutes has a different glycemic index than pasta boiled for 15 minutes), when it is eaten relative to when it was cooked (potatoes often have a higher glycemic index when eaten after cooking than they do if refrigerated  and then reheated and eaten the next day), how ripe the food is when eaten (generally, the glycemic index of fruit increases as the fruit ripens), or which variant of the food type you are eating (different types of raisins have different glycemic indices).
  2. Glycemic index for a particular food varies depending on what is eaten along with that food.  Fat, protein or fiber eaten along with a particular food usually results in a lower overall glycemic index.  For example, you’ll usually get faster blood glucose from raisins eaten alone than the raisins in a cookie.
  3. Different people will have a different glycemic index for the same food because individuals differ in how efficiently they digest carbohydrates.  In addition, the same person may have a different glycemic index for the same food when that food is eaten at different times of the day.
rough categories

The glycemic index values that are used to define the categories in this image are rough guides.

Considering all of these factors, I think the glycemic index can be modestly useful to the cyclist planning what to eat during a ride.  There are many glycemic index charts for different foods that can be found on the internet.  The specific numbers given in these charts are best thought of as rough estimates.  For the cyclist it’s probably most useful to consider glycemic index in terms of three rough categories: High, medium and low glycemic index foods.  High glycemic index foods will probably provide needed glucose throughout the ride.  On long rides of two hours or more, low glycemic index foods can produce needed glucose later in the ride if the food is eaten early in the ride.  As you get closer to the end of the ride, higher glycemic index foods are more likely to be beneficial while you’re still on the bike.

WARNING:  The nutritional needs of a person engaged in 60 to 90 minutes of moderate to intense exercise or a long ride lasting more than 2 hours are very different from the nutritional needs of that same person going about their daily activities.  High glycemic foods can be very useful while you’re on the bike.  A steady diet of high glycemic foods when you’re not engaged in endurance exercise has been shown to be related to various health problems such as obesity (and all of its related problems), diabetes and, at least in animal studies, a shortened life span.  High glycemic foods eaten while you’re riding will generally help you.  A day-in, day-out diet of high glycemic foods when you’re not exercising will generally hurt you.

Cycling Nutrition: Eating After the Ride

Post ride recovery in Ireland

The information in this post has been revised and substantially enhanced in Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride which can be purchased on  The revisions include new information about the relationship between protein and carbohydrates in post-ride recovery based on research published after this post was written. The book also has new sections devoted to rehydration and glycogen, protein, and electrolyte replacement following the first hour after you get off the bike. For information about Nutrition for Cyclists and how it relates to what I’ve posted to Tuned In To Cycling, please check out this post.

I’ve seen this happen time and time again.  Laura and I have had the good fortune to go on several bicycle tours that last one to two weeks.  The tours are advertised for advanced or experienced riders and typically feature hilly or mountainous terrain and daily rides in the 60 to 125 mile range.  You ride from place to place and a van carrys your luggage.  The other riders on the tour are almost always experienced cyclists, at least in the sense that they have been riding for many years and are used to riding long miles.  These tours usually schedule a day or two off when the riders are free to do whatever they want.  This has always puzzled me.  Why would experienced cyclists pay the steep cost of going on one of these tours, go through all the hassle of getting their bike to some exotic location, and then spend a day or two not riding in terrain that provides spectacular cycling?  The people who run these tours obviously know more about it than I do because by the third or fourth day of the tour almost all of the riders are noticeably lacking in energy and enthusiasm, are irritably fretting about why they feel so tired, and are looking forward to the break.  Meanwhile, Laura and I are riding extra miles every day because we’re having so much fun, are fresh and ready to go every morning, and are typically the only ones out on our bikes on the day off.

What’s going on?  Why are we riding more miles with less overall fatigue than almost all of the other riders?  I don’t know for sure, but I’m fairly certain the answer lies in post-ride nutrition.  Many of these other riders are active members of their local cycling clubs.  They shine on organized centuries and long weekend rides with members of the club.  After the ride everyone goes out for ice cream or pizza and beer.  They are clueless about post-ride nutrition and have given no thought at all to how what they eat when they get off the bike can affect how they will ride the next day and the day after that.  They finish the first day in glycogen debt and fail to adequately replenish their glycogen stores before the next day’s ride.  Every day the situation gets worse and the riding becomes more unpleasant until by the third or fourth day their blood sugar levels are so low they’re grinding it out with their head down and need a day off to physically and mentally recover.  All of this can be avoided if you pay attention to what’s happening in your body when you get off the bike and take advantage of the opportunity your body gives you to prepare for strenuous activity on the following day.  Most of it comes down to what you eat in the first 30 to 40 minutes after you get off the bike.

When you finish a long ride your glycogen stores are exhausted and you are very likely to have low blood glucose.  Your body responds to the glycogen debt by going into overdrive to replace the missing glycogen.  Excess glucose in the bloodstream is converted to glycogen and stored in the muscles and the liver.  Under normal circumstances insulin is used in this conversion process.  However, after an extended period of exercise when the muscle glycogen stores are exhausted an abbreviated and accelerated glycogen-storage process kicks into gear that converts glucose into glycogen and stores it in the muscles without the need for insulin.  This period of intense glycogen production and storage lasts for 30  to 60 minutes.

In order to take advantage of this brief period of accelerated glycogen storage the system must have blood glucose that can be converted to glycogen.  And there’s the problem.  When you finish a long or intense ride you are almost certainly low on blood glucose.  Your system is ready to rapidly and efficiently replenish your empty glycogen stores but it doesn’t have the glucose it needs to make the glycogen.

The solution is to flood your system with carbohydrates that can be quickly converted to blood glucose which will in turn supply the accelerated glycogen production and storage mechanism with the glucose it needs.  Although the enhanced glycogen production mechanism will operate for roughly 60 minutes after exercise has stopped, keep in mind that it takes time for carbohydrates in the stomach to be broken down into useable blood glucose.  Food you eat during the second half of that 60 minute window may still be in the stomach being digested when the enhanced glycogen-storage process ends.  The first 30 minutes after you get off the bike are critical.  If you are going to fully replenish your glycogen stores for the next day’s ride, you must ingest enough carbs during those 30 minutes to flood your system with glucose.  If you don’t, it doesn’t matter what you eat for the rest of the day; you will be building on a weak foundation and you won’t have the glycogen reserves you need to ride with strength day after day.  This cannot be stressed enough; you have to reload your system with carbs during the first 30 minutes after you get off the bike.

How many carbs do you need to eat during the critical 30 minutes?  Current thinking holds that you should aim to ingest one half gram of carbohydrate for each pound of body weight during the 30 minutes after you get off the bike.  This is easy to figure out; simply divide your weight in half and eat that many grams of carbs.  For example, I weigh about 160 lbs so I need to eat 80 grams of carbs within 30 minutes of getting off the bike.  There is also some evidence that combining these carbs with protein may facilitate the glycogen production and storage process.  The recommended ratio of carbs to proteins is 4 to 1.  Thus, at 160 lbs I need 80 grams of carbs and 20 grams of protein.

Eating enough food to provide this much carbohydrate in the first 30 minutes after you get off the bike can be very difficult.  The 30 minute part is much more important than the specific amount of carbs and protein part.  If you can’t manage to choke down the full recommended amount, eat as much as you can, but make absolutely certain you do it in the first 30 minutes after you get off the bike.

You can eat any kind of food you like as long as it’s high in carbs.  Simple carbohydrates that can be more quickly broken down into blood glucose are better than complex carbohydrates that take a longer time because you need to get the glucose in the blood stream within a short window of time.  There are two key factors that will end up driving your 30 minute carbohydrate feast; the food has to be available immediately when you get off the bike, and you have to be willing to eat it.  The carb sources you’ve been eating on the bike will work equally well during this critical 30 minute window but you may be sick and tired of sports drink, energy gel, low-fat fig newtons or whatever you’ve been eating by this time.  Laura and I drink a Endurox - picture from accelsport.comrecovery drink called Endurox that contains carbs and proteins in the recommended 4 to 1 ratio.  We find it’smuch easier to drink a large number of carbs than eat them immediately after a long ride.  It’s also very easy to have the drink ready at the end of the ride.  Endurox comes in a powdered form that you mix with water.  We premeasure the powder, put it in a baggie, and carry it with us on the ride.  Water is almost always available at ride’s end and we simply mix the powder with fresh water in our water bottle and chug it down.  Although the manufacturer would have you believe otherwise, there’s nothing special about Endurox other than that we like the way it tastes.  A number of companies make recovery drinks that provide huge carbohydrate loads for immediate post-exercise glycogen replacement.

After the critical 30 minute window, try to continue to ingest carbohydrate at regular intervals throughout the remainder of the day.  Eat small amounts steadily rather than eating nothing and then pigging out at dinner.  Avoid alcohol because it will interfere with the uptake of glycogen and will also dehydrate you.  Avoiding alcohol is especially important immediately after the ride when the body is in the critical glycogen restocking period.

What you eat during the 30 minutes after you get off the bike is probably the single most important factor affecting how you will fare if you’re riding more than 90 minutes a day for more than 2 days.  If you get the carbs you need during this 30 minute window, you can ride for days and days without problems; if you don’t, you’re most likely going to be tired and out of energy by the third or fourth day.

For more information about what to eat (and what to avoid eating) after a ride, see Eating After the Ride Part 2.