Carbohydrates 101
Carbohydrates are the high-octane fuel of choice for your body. With a yield of only 4 calories per gram carbohydrates are also a very precious source of energy for physical activity. The normal endurance athlete diet should obtain about 65% of total daily calories from the intake of carbohydrate. Your body is always working to keep glucose levels in the blood constant under all conditions. Under periods of great physical exertion this can be very challenging. Your understanding of where carbohydrates come from and how to use them the most effectively will make life on and off the bike much more enjoyable.
More Than You Ever Wanted to But Need to Know
Carbohydrates are found in two basic forms, simple and complex. Simple carbohydrates are the most common form and are made up of single sugar molecules known as Monosaccharides and double (two bonded together) sugar molecules called Disaccharides. Complex carbohydrates are the preferred energy source for endurance bike riders and are made up of even longer chains of single sugar molecules called Polysaccharides.
Monosaccharides do not require digestion to separate the sugar molecules before absorption and deliver energy to the body very quickly. The most common forms of Monosaccharides in your diet are sucrose (table sugar) fructose (fruit sugar) and lactose (milk sugar). Other sources of simple sugars are dextrose, syrups and other refined sugar products and alcohol.
Disaccharides and Polysaccharides (bonded sugar molecules) must be digested and separated back into single sugar molecules before they can be absorbed and transported to the cells in the bloodstream. The most common forms of Disaccharides and Polysaccharides in your diet are pasta, grains, breads, rice and other forms of starch. Complex carbohydrates are the best energy source on the bike because they deliver their energy more gradually.
Once in the body, carbohydrates are metabolized (converted to an energy unit like ATP) to provide energy for use by the cells or stored in liver and muscle cells as glycogen to be used for future energy needs. When carbohydrate intake exceeds current energy needs and muscle/liver storage capacity it is converted and stored as adipose tissue (fat).
All Sugars are not Created Equal
Carbohydrates differ greatly in digestion, absorption and potential effect on performance. The most important trait of any energy source is the rate at which it becomes available once it is in the body. For carbohydrates this is called the GI, or glycemic index. The glycemic index represents the rate at which the sugar molecules can be digested and absorbed into the blood stream based on pure glucose, which has a GI of 100. Energy foods are grouped into three categories based on GI:
High (GI above 85) include breads, grains, white rice, potatoes, cereals, raisins, glucose based sports drinks and corn and maple syrup.
Medium (GI of 60-85) include corn, oatmeal, bananas, pastas, white sugar, yams, tropical and citrus fruits.
Low (GI below 60) include milk products, non-citrus fruits, peanuts, lentils, apples and frutose.
Foods with a higher GI will raise blood sugar levels quickly and trigger an insulin reaction that helps supply energy faster to working and recovering muscles. During exercise or competition there is heavy dependence on stored muscle glycogen for energy. As muscle glycogen levels fall there is an increased reliance on digested glucose circulating in the blood stream. Consuming medium and high GI foods and sports drinks will help to keep blood sugar levels up and help spare glycogen.
The best strategy for good muscle glycogen management begins with consuming medium and high GI foods and liquids at the very start of the event or workout. Near the end of a long workout or during the finale of an event ( the last 30-45min) there will a greater dependence on glucose for quick energy delivery so switching to high GI foods are makes sense. Once the recovery process begins continuing the intake of high GI combined with a little protein, will enhance the insulin reaction and facilitate the quickest replenishment of muscle glycogen.
Using Sports Drinks
Many different forms of liquid carbohydrate are available for cyclists. You can choose from fruit juices and cola drinks to the highly touted and very popular engineered sports drinks made with glucose polymers like maltodextrin and other exotic ingredients. For many riders taste is often the strongest factor in choosing a sports drink so the trick is to find the mix that works best for you in the maximum concentration that will empty from your stomach and not give you any upset.
It is commonly believed that “experienced” riders can tolerate concentrations up to 10% carbohydrate while 6%-8% is the most common solution found in the bunch. Gastric tolerance and the rate at which carbohydrate empties from your stomach without causing nausea or indigestion will determine what concentration you can tolerate. High concentrations (8%-10%) of simple sugars can delay emptying and cause nausea. The best course is to mix your drink to the manufactures instructions and then experiment with different doses. Don’t be surprised if you need a lower concentration in the hotter weather. Warm liquids do not empty very quickly from the stomach and having lots of sugar sloshing around in your gut will likely make you feel a bit upset.
With all the attention given to the glucose polymer sports drinks they do not seem to effect performance any better than the old standards like fruit juice, colas and Gatorade. Canned colas and fruit juices and other (glucose) simple sugar drinks have carbohydrate concentrations of around 10% so the calorie yield is very similar by volume. However, the strong sweetness of these drinks and potential stomach upset from the simple sugars present the biggest problem most for riders. An upset stomach will not empty well preventing delivery of the much needed energy and fluids to the body. This accounts for much of the popularity of the complex carbohydrate sports drinks made with glucose polymers and other ingredients that are easier on the stomach.
Keeping the Tank Topped Off
The depletion of muscle glycogen can happen slowly over a period of several days of training and competition. The symptoms of chronic glycogen depletion are similar to those of over-training; excessive fatigue, heavy legs, diminished performance and poor recovery. The goal of your nutritional strategy is to maintain optimal levels of muscle glycogen and always have enough fuel available to support the work you want or need to do on the bike. A traditional method for this has been the infamous carbo-loading. This involves letting carbohydrates become depleted below normal levels and then slamming in all you can in the days prior to the event. The theory is that starving the body will cause greater uptake once the carbohydrates are presented in the diet.
The necessity to carbo-load says that you are not managing your diet correctly and are approaching an event with less than optimal fuel on board. As a competitive bike rider you will often times burn calories faster that you can take them in and this produces a deficit that is covered with stored glycogen. There are some strong arguments that support increasing complex carbohydrate intake a bit, say 10%-15 % over normal levels, in the days preceding an important event just as an insurance policy against coming up short on the big day but this is not thought of as carbo-loading.
A good diet will supply you with enough stored carbohydrate to support up to 2 hours of cycling at around 70% of your Max V02 without risking the bonk. However, it is foolhardy to support even this moderate an effort with stored energy alone. Remember that you are always burning fat and oxygen (oxidative metabolism) for energy regardless of the intensity of your effort. Once you hit about 50% of V02 you involve glycolysis (carbohydrate metabolism) to support the higher intensity work. The combined energy systems provide the ATP needed for more aggressive riding.
Past the 2 hour mark you will run into serious problems unless you have been reducing glycogen depletion with supplemental carbohydrate intake from medium and high GI sports drinks or solid food to maintain blood glucose levels. Eating properly on and off the bike will eliminate most fuel shortage problems. My advice is to stay away from this nonsense of carbo loading, follow a sensible eating plan to keep you diet on track and get into the habit of eating better on the bike.
How Much?
There is plenty of controversy as to the proper amount of carbohydrate in the endurance athlete diet. The most common notion is that 60 to 70% of total calories need to come from carbohydrate. From a coaching standpoint I agreed and the best way to determine an athlete’s carbohydrate calorie needs is to look at the type of riding they do, their aerobic fitness and their body composition (% body fat).
First, if an athlete needs to trim down then they need to burn more stored body fat for energy and less carbohydrate. Reducing carbohydrate intake while increasing aerobic training volume is the most sensible approach. The increased dependence on oxidative metabolism will reduce the need for dietary carbohydrate intake. On the flip side, maintaining optimal body fat levels is important to your performance and health. If too many of your calories are from carbohydrate than you will be low on dietary fat intake and this can present a host of problem from diminished performance and strength to illness.
The intensity at which you ride controls the energy systems being used. If you do mostly long distance riding like centuries and touring than you are mainly a fat burning machine. If you are a track sprinter or a criterium specialist than carbohydrate is your best friend. In all cases increasing your dependence on your aerobic energy system will help spare your glycogen stores. For training purposes the best approach is to rely on both energy sources so that your glycogen stores do not become depleted and you have enough fuel on board to do the training that you need. For competition or major events carbohydrate intake will play a major role in the success of your day.
The simplest way to manage your carbohydrate intake is to look at your daily needs based on intensity and recovery and your body weight and not focus on the percentage of your dietary calories. Start first by determining your average total daily calorie needs based on your BMR (basil metabolic rate) plus the calories needed to support your training and competition. See Basic Cycling Nutrition Plan for more information on calculating your daily calories.
Assuming you are an endurance cyclist and do not need to loose any weight you can figure you daily carbohydrate intake to support all your activities based on the following. A recreational level rider requires about 4-5 grams/ kilogram of body weight/per day. A competitive rider will easily need 6-8 grams/kg/day and elite level riders, like pro stage racers can require up to 10 grams/kg/day just to keep the pedals turning.
The following is a short list of foods that supply carbohydrate from a variety of sources.
Putting it All Together
As with the rest of your cycling preparation, keep it simple. Don’t get crazy with your diet. Being a bike rider is difficult enough already. Educate yourself about the kinds of foods you need and you should be just fine. Some athletes, like vegetarians, diabetics and those with food allergies need extra help. If you are having trouble finding a simple and balanced eating plan you might a candidate for a session with a sports nutritionist to help you sort things out.
Design your eating plan around supplying the needed carbohydrates for your level of riding and body weight and simply fill in the rest of the calories with an appropriate mix of fats and protein. If you experience peaks and valleys in your energy levels you might be relying too heavily on simple sugars. Increase your intake of complex carbohydrates and see I you can eliminate the drastic energy swings. This applies to your normal activities as well. Keep a good balance of simple and complex carbohydrates in your diet.
Under extreme conditions a rider can easily burn 600-800 calories per hour exceeding the calories available from digestion and making muscle glycogen depletion a major concern. During peak recovery periods increase your intake of simple sugars to stimulate the insulin response and increase the rate of glycogen uptake to the depleted muscles. Pay close attention to how different sugars affect your stomach and performance. Experiment with different foods, drinks and gels during your training to find that perfect combination. Try simple sugars for a quick burst of energy or a bagel or other complex carbohydrate for more sustained energy.