Cycling Nutrition: The Bonk

Posted on May 10, 2008 by Kevin Murnane

The information in this post has been moderately revised and combined with information about cramping, dehydration, and electrolyte loss in Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride which can be purchased on Amazon.com. 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.

So . . . you know that muscles burn glucose for fuel, your body stores enough glucose in the form of glycogen to fuel about 90 minutes of moderate exercise, and you need to ingest carbohydrates to provide more glucose for longer or more strenuous rides. You know about what to eat and when to eat it to get the carbs you need while you’re on the bike. But you keep hearing about this “bonk” thing. You keep hearing you’ll bonk if you don’t get the carbs you need. What’s this bonk everyone keeps talking about? Believe me, you don’t want to know. At least you don’t want to know on the basis of firsthand experience. Reading about the bonk so you know what it is and how to avoid it is good. Having a bonk is not good.

Eat before you're hungry

“Bonking” is what cyclists call hypoglycemia which is the medical term for abnormally low levels of blood glucose. You bonk when you have exhausted your glycogen stores, haven’t ingested enough carbs to produce more blood glucose, and are still riding the bike. Anyone can bonk if they don’t eat properly on the bike. Lance Armstrong, who probably knows as much about cycling as anyone on the planet, got wrapped up in the race on a stage in the 2000 Tour de France, forgot to eat, and bonked on the climb up the Col de Joux Plane in the French Alps. The only reason he didn’t lose the Tour de France that day is because he had an iron will and an inhuman capacity to suffer. Afterwards he called it the worst day on the bike he’d ever had.

Bonking can be especially deadly for cyclists because your muscles aren’t the only things in your body that burn glucose for fuel. Your brain burns glucose too. That means that not having enough glucose in your blood to fuel the system has mental and emotional effects in addition to physical effects. If blood glucose levels drop too low, the body will act to protect the brain and will begin to shut down the muscles first. However, the muscles won’t completely shut down before the brain begins to be affected and the mental and emotional consequences of bonking can be more dangerous to the cyclist than the physical consequences.

When you bonk, physical exertion becomes extraordinarily difficult. Your muscles don’t have the fuel they need to operate effectively and forcing them to work becomes more and more difficult. You feel extremely weak and lethargic. You may tremble and shake uncontrollably and sweat profusely. You feel dizzy and light headed. Your sense of balance is upset. You may have heart palpitations. You will probably feel ravenously hungry. On the mental and emotional side you will probably feel nervous and anxious. You may become confused and disoriented. You will have low emotional control and will become hostile, belligerant and easily irritated. You may experience overwhelming feelings of being defeated, hopeless and unable to go on. Your awareness of what’s going on around you will shrink and can arrive at an extreme form of tunnel vision in which the only thing you’re aware of is the spot on the road ahead that you’re staring at. You may have difficulty speaking. At the extreme, hypoglycemia can produce seizures and coma. In a word, it sucks.

What do you do if you bonk? You need to get your blood glucose levels up and you need to do it quickly. Ingest simple carbohydrates that can be rapidly processed into blood glucose by the digestive system. The best source for these kinds of carbs that you’re likely to have with you on the bike is a sports drink like Gatorade. Other sources of simple carbohydrates include energy gels (make sure you drink plenty of water with these), sugar cubes or sweet candy like gumdrops or jellybeans. Complex carbohydrates like energy bars will take longer to process into blood glucose and will only provide relief in the longer term. If you catch the bonk early, you can keep riding while you refuel. If you let the bonk go too far, get off the bike until you recover. You don’t want to be riding when your sense of balance is bad, you’re disoriented and you’re unaware of what’s going on around you.

After you’ve bonked and begun to recover, pay careful attention to what you eat for the rest of the ride and make sure you keep your glucose level up by regularly and frequently taking in fast absorbing carbs. Sports drinks are very good for this. Perhaps the hardest part of reacting to a bonk is mental. You need to try and be aware that you’re not thinking clearly and not being as aware of what’s going on around you as you need to be to ride safely. Forcibly arouse yourself from your lethargy and pay extra attention to what’s happening around you. Of course this is easier said than done; it’s not easy to be aware that you’re not thinking clearly when you’re not thinking clearly.

Whether you’ve started to bonk or not, try and get in the habit of monitoring yourself for the early signs of a bonk. The ride beginning to feel like a chore? Getting irritable and angry? Not paying as much attention to what’s happening around you? If you catch it early and replenish your blood glucose before it gets out of hand, you can usually keep riding safely and effectively. If you have a regular riding partner whose riding abilities and demeanor on the bike are familiar to you, be aware of their condition as well. A rider who isn’t thinking clearly is likely to misinterpret or misunderstand what’s happening to them in the early stage of a bonk. Help them out. Be aware that you may have to treat them carefully as they may be experiencing increased levels of irritability and hostility combined with decreased emotional control. If you think you might be bonking, tell your ride partner so they can help you.

Most of the time bonking happens when you’ve ridden for a long time and haven’t been eating properly. However, a bonk can also happen in unexpected circumstances. Laura and I once rode in a week-long cycling tour through the Rocky Mountains in the Glacier National Park area in Montana and Canada. We approached this tour as a cycling vacation rather than a training opportunity and rode at a much slower pace than we usually do. We also stopped and had lunch mid-ride with other riders on the tour which was something we had never done before. The lunches were great with good company and good food but we had no experience in how to incorporate eating a meal like this into a long ride. The first time we had lunch mid-ride I completely screwed it up. We continued riding after lunch and when we were about 20 miles from finishing I began to experience the early stages of a bonk. What had happened? I hadn’t pigged out at lunch but even a small lunch was much more than I would typically eat during a ride. My stomach was full and the idea of eating either didn’t occur to me or, if it did, it wasn’t attractive. Although my stomach was full, it was full of mostly protein and fat which could not be broken down fast enough to provide the energy I needed to finish the ride. I was getting very little glucose from the food I’d eaten and my glycogen stores were exhausted so I started to bonk and didn’t recognize it for what it was. Those last 20 miles were miserable; the temperature had dropped, we were riding directly into a strong headwind, and I was completely demoralized and shivering uncontrollably by the time we reached the lodge where we were scheduled to stay the night. Fortunately, the lodge had an enormous fire roaring in the center of the main area with a bench-like hearth running around it on all four sides. While we waited for the van to arrive with our luggage, I sat huddled by the fire in a private little world of misery slowly recovering and getting warm. The lesson I learned? You can bonk on a full stomach if your stomach’s full of the wrong things.

As unpleasant and dangerous as bonking can be, the good news is that it’s easily avoided. Start your clock as soon as you get on the bike and eat regularly and properly throughout the ride and you’ll never have to experience a bonk. Eat before you’re hungry, eat before you bonk.

Cycling Nutrition: Eating on the Bike

Posted on May 10, 2008 by Kevin Murnane

The information in this post has been revised and enhanced in Nutrition for Cyclists: Eating and Drinking Before, During and After the Ride which can be purchased on Amazon.com. The enhancements include increased attention given to how fats are processed during the ride, an easy-to-calculate metric for evaluating whether different foods are likely to make for good on-the-bike eating, and an extended section on keeping hydrated during the ride. 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’m continually amazed at the things I see cyclists eat during and after rides but am never surprised to see the effects ranging from loss of energy, through loss of concentration leading to mistakes and sometimes injury, to a full-fledged bonk. The basic roles played by glycogen storage, blood glucose and the extraction of glucose from ingested carbohydrates are well understood as is what you need to do to avoid nutrition-based problems while you’re riding. That doesn’t stop riders from falling prey to these problems all of the time, however. Sometimes cyclist’s ideas about nutrition are based more on currently popular nutritional fads than sound knowledge. Sometimes riders have an emotional commitment to eating particular foods and don’t want to change. And sometimes you know what to do but you just can’t bring yourself to do it. Whatever the reason, ignoring basic endurance nutrition almost always means trouble.

As detailed in another post, muscles burn glucose for fuel and the body stores glucose in the form of glycogen which can be broken down into useable glucose when working muscles need an increased fuel supply. The body can store enough glycogen to support approximately 90 minutes of moderate-intensity exercise. If you are going to ride more than 90 minutes, or if you are going to experience periods of high intensity riding, such as strenuous hill climbing, on a ride of less than 90 minutes, you are going to need to get glucose to fuel your muscles from food you ingest during the ride.

What kind of food should you eat? The answer is well known and well supported by decades of research into endurance athletics. Carbohydrates. Why carbohydrates? Primarily because their chemical structure is such that they can be broken down quickly and efficiently into useable glucose. Glucose can be derived from fats and proteins as well as carbs and fats might seem to be an especially good source of energy because fats have roughly twice the number of calories as carbs or proteins. The problem with both fats and proteins is that the process of breaking them down to extract useable glucose takes a long time and is inefficient. You have to burn more energy to extract glucose from fats than you do to extract it from carbs. In fact, fat metabolism (the process of breaking the fat down) requires carbohydrate that could have been more efficiently burned for glucose if wasn’t used to break down the fat. Moreover, and possibly of more importance to you while you’re on the bike, it takes a fairly long time to extract glucose from fat or protein. If you eat fat or protein loaded food during a ride, the ride may well be over by the time the fats and proteins have been processed to the point where you can get energy from them. In the meantime, all the energy used in breaking down the fats hasn’t been available for powering the muscles. Carbs, on the other hand, can be broken down quickly and efficiently to provide the glucose needed to keep going on the bike. They are absolutely essential for the long-distance cyclist.

Where do you get the carbs you need during a long ride? Some high-carb foods like pasta and rice are impractical to eat during a ride; you need high carb, low fat foods that you can easily carry with you on the bike. Good on-the-bike foods include dried fruit like raisins or dates, bagels, and low fat bite-sized cookies. Energy bars are a terrific source of carbs. For example, a single Powerbar has 45 grams of carbohydrate and only 2 grams of fat. There are also energy gels made specifically for endurance athletes such as Power Gel or Goo that have very high doses of carbs. If you eat high density carb supplements like energy bars or gel, make sure to drink plenty of water with them or they will sit like sludge in your stomach and you won’t get the quick transfer of carbs into blood glucose you need. Another excellent source of carbs are sports drinks like Gatorade. These drinks are usually loaded with carbohydrates and although they are marketed as important sources of electrolytes, the carbs they supply are probably of much more importance for the endurance cyclist.

When do you eat? A common cycling mantra is “Eat before you’re hungry and drink before you’re thirsty”. This is excellent advice. By the time the body reacts to low levels of fuel or fluid and sends hunger and thirst signals it’s too late. Rather than stopping and eating a large amount of food (such as lunch) mid ride, nibble high carb foods frequently throughout the ride. This not only provides immediate glucose, it can help protect the body’s glycogen stores; if the muscles are burning glucose from the low-fat fig newton you just ate, they’re not burning your stored glycogen. Try to ingest some carbohydrates every 30 minutes or so. Start eating during your first hour on the bike. The sooner you begin drawing needed energy from food intake the longer you can keep a reserve of stored glycogen.

How do you carry the food? Eating on the bike isn’t easy, especially in the first hour when you probably won’t feel hungry. Stopping to eat makes eating even more of a hassle which makes it more likely you’ll skip it. Bad idea. When pros like the rider in the picture at the top of this post ride in a race, they have feed zones where they pick up a musette bag filled with enough food to get them through the next segment of the race. You won’t have this luxury so you’ll have to carry nibble food in a fanny pack or your rear jersey pockets and learn to eat while you ride. Because I don’t like to hassle with getting food out of wrappers or putting uneaten food away while I’m riding, I usually bring bite-sized foods with me on the bike. If I have something larger like a Powerbar, I cut it up into bite-sized pieces before the ride. To get at food easily I put it in a baggie and then roll the baggie up without sealing it. When it’s time for food, I simply unroll the baggie, reach in and pull out something to eat. No fuss, no muss and no garbage like food wrappers to put away when I’m done. It takes a surprising amount of practice to get in the habit of eating regularly on the bike. Practicing eating may sound like a crazy idea but it’s very easy to forget and run into trouble later. Note the time your ride starts and make yourself nibble some food every 30 minutes.

What’s the best kind of food to eat on the bike? Disciplining yourself to eat by the clock on the bike is difficult. It can be a hassle to get out the food, riding with food in your mouth can be unpleasant, and sometimes eating can be the last thing you feel like doing. For all of these reasons one of the most important considerations when deciding what kind of food you should bring with you on the bike is whether or not you’ll actually eat it when the time comes. Having some kind of goo, gel or energy bar with you that is marketed as “scientifically proven” to be the optimal energy source for the endurance athlete and is endorsed by famous cyclists is useless if you won’t eat it because you think the stuff tastes like shit or feels disgusting in your mouth. It’s easy to find an excuse not to eat when you’re on the bike. Bring food that is mainly carbs but bring food you like. It’s better to get a little fat with your carbs by eating a low-fat bite sized cookie than getting no carbs at all because the thought of a mouthful of Goo makes you want to puke. Experiment with different foods to find a combination that is high in carbs and low in fats and proteins that you will eat while you’re on the bike.

Can I have too many carbs? If you’re going to be ingesting large amounts of carbohydrate during the course of a ride, you should be aware that high concentrations of carbohydrate in the stomach can cause gastrointestinal distress such as nausea. The more you rely on dense carb sources like gels and energy bars, the more you’re likely to run into this problem. If you listen to live broadcasts from multi-day stage races like the Tour de France you will frequently hear reports of professional riders that are having gastrointestional problems during the race. Individuals vary widely in their sensitivity to carbohydrate concentration so you will have to experiment to find your limits. If you’re feeling nauseous, drink water to reduce the concentration of carbohydrate in your stomach and lengthen your feed time until you feel better.

What happens if I don’t eat? Ingesting carbs while you’re cycling isn’t always easy and it it isn’t always fun but it’s absolutely necessary if you want to have the energy you need to finish your ride. Failing to take in the carbs you need can lead to pronounced losses of energy and strength, reduced awareness of what’s going on around you, and increased irritability and hostility, all combined with the feeling that finishing the ride is an unbearable and impossible task. In other words, you could bonk. Not eating can turn a pleasant ride into an unpleasant one or a challenging ride into a nightmare. Eat before you’re hungry and continue eating throughout the ride.

The ride’s over, now what? If your’re going to ride for two or more days in a row, what you eat iimediately after a ride is as important as what you eat during the ride. Find out about post-ride recovery here.