It is sometimes difficult to assess the effect of diet on athletic performance. While some riders seem to do well no matter what they eat many unknowingly handicap themselves with less than optimal eating habits both on and off the bike. Most elite cyclists do watch their diets very carefully and will attest to the value of eating intelligently. These riders are sensitive to the subtle physical signs of different dietary regimes. Whether you're interested in becoming a successful athlete or just getting fit here are some tips on what to look for and look out for.
During any workout blood sugar is the primary determinant of how well you feel and perform, therefore it is vitally important to eat during any ride longer than 1 or 2 hours. The calories burned in these rides must be at least partially replaced during the workout or blood sugar will drop and you will feel tired. Most riders misinterpret this fatigue as lack of endurance but very often it's simply low blood sugar.
By eating every 15 to 20 minutes after the first 45 minutes of a ride you can avoid this "false fatigue". First you'll need to plan ahead, purchasing and packing food, and remembering to eat lightly and regularly; bananas, fig bars, Clif Bars, fruit juice diluted with water, etc. All these foods are readily available and easily digested on the bike. Avoid high-fat foods, they can slow you down, and simple sugars that can cause an insulin reaction resulting in lower blood sugar levels after an initial boost.
Eating while working-out does not come naturally. The physical stress of exercise depresses the brain's hunger center. This is especially true during extreme effort when hunger might not appear until blood sugar has dropped dangerously low. If during a long hard your ride blood sugar falls low enough to cause hunger take it as a bad sign. It may not be wise to continue riding and you may need a prolonged (12+ hours) rest.
Not eating enough on a long ride will usually result in "the bonk". At one time or another every serious cyclist will experience it. When blood sugar falls so low that further exercise becomes difficult, that's the bonk. Should it happen to you find something sweet to eat _right_away_ and finish the ride via the easiest possible route. Do not wait to eat and don't ride any further than necessary. It is possible to become so (physically) stressed from bonking that you wake up sick the next morning. Even if you do not get sick, you probably won't derive any positive training effect from the ride. Recovery generally takes so long that you actually lose fitness, even if the workout had been high quality initially.
Normal levels of blood sugar (glucose) are also essential for metabolizing fat. Thus, when blood sugar runs low fat cannot be metabolized to compensate. This becomes important as fat utilization rises after the first thirty minutes of exercise. In order to burn fat you need to ride for at least half an hour - without getting hungry doing it. It simply is not possible to burn fat by eating less during a workout. Only by putting in long miles and eating intelligently is it possible to become more efficient at burning fat. Glucose is also the only fuel the brain can use. Training in a glucose-poor state makes it difficult to think clearly and is a real safety risk.
Thirst is similarly suppressed during strenuous exercise. Though trained athletes are generally able to judge how much to drink, large fluctuations in need can occur due to fatigue, temperature, altitude, humidity, air flow, fitness, food and the type of fluid consumed. Dehydration can be deceptive because it feels exactly like fatigue. Late in a hard ride, when you feel tired, it may simply a case of dehydration. Don't sell yourself short, drink up before getting tired.
A fluid loss of as little as three percent of total body weight (4.5 of 150 lbs.) can measurably effect performance. Dehydration impairs thermoregulation through reduced sweating and blood circulation. As dehydrated blood gets thicker it creates cardiac stress which impairs the metabolic processes necessary for physical effort.
Losing more than a few pounds on a ride, or more than a couple of pounds overnight, is a good indicator that you didn't drink enough. With experience it will become easier to keep within a few pounds of pre-race weight even on long rides in hot weather.
Research indicates that the most likely reason electrolytes are eliminated in sweat is to compensate for rising concentrations in the bloodstream. This fluid / electrolyte balance arises after drinking less than is eliminated in sweat and urine or used by other metabolic processes. Supplementation with electrolyte-containing sports-drinks adds to this imbalance and can hasten fatigue by increasing volemic (as opposed to osmotic, or intra-cellular) dehydration.
The average athlete's diet contains far more electrolytes than they could ever lose through sweat in all but the most extreme ultra-endurance events or cases of heat exhaustion.
Many commercial sports drinks offer little more value than diluted fruit juice or sugar water. Of all the studies done on sports drinks and performance only one has shown a statistically significant effect. The American Dietetic Association (1981) showed a decrease in the performance of athletes drinking fluids containing electrolytes when compared with straight water. This should not be read as a blanket endorsement of plain water since fluids with carbohydrates are absorbed faster than plain water alone. Electrolytes, however, pull fluids out of the bloodstream and into cells where they are normally less effective in compensating for fluid losses brought about by sweating and physical effort.
Overly sweet fluids too, can hurt performance. Sugar concentrations over 100 calories per water bottle slow the absorption of fluid and, except for fructose, can cause an insulin reaction. The high sugar concentration of some commercial drinks also lessens their effectiveness in preventing dehydration.
On the other hand, one of the best sources of quick energy is the water bottle, especially for shorter races. Watch a pro peleton in Europe: in the final kilometers you will see riders pulling small flasks out of their pockets and drinking the contents. These flasks usually contain a dextrose/glucose solution that quickly and temporarily raises blood sugar. The extra sugar can be a tremendous advantage during the final sprint.
There is some controversy in sports-med literature regarding the optimal sugar concentration of fluid taken during exercise. Many of these studies fail to consider that sub-maximal fluid absorption may be appropriate when much-needed calories are also absorbed. Despite the debates, most cyclists learn by trial and error what fluids work best and in what quantities.
Many endurance athletes opt for a full-time high carbohydrate diet. While such a diet might be beneficial before a competition, it is not a good idea to let daily protein intake fall below 14 to 20% of total calories. Not only is the amino acid pool tapped for fuel during endurance exercise, amino acids also play an important role in muscle metabolism (primarily in acid buffering and the glucose-alanine cycle).
Among the many disadvantages of a negative nitrogen balance (protein deficit) are reduced healing and recovery abilities, immune system suppression and muscle atrophy. Have you noticed how thin cyclists can get after a few months (or days, in some cases) of putting in serious miles? Not just low body fat but honest, muscle and bone skinny. That kind of weight loss is undesirable even if it helps you climb better. this sort of weight loss is due to muscle tissue being converted into fuel (gluconeogenesis) when other sources of energy run low. This muscle is not regenerated if the amino acid pool is tapped for energy and your diet is low in protein (measured as percent of total calories NOT grams per day). You can lose weight but still not become a fitter, better rider.
On the contrary, protein malnutrition will depress your immune system, retard recovery from hard workouts, slow healing and impede many other processes, both physical and mental, necessary for athletic success.
Though cholesterol levels are rarely a problem for racing cyclists, a high fat diet can effect performance, especially for track and criterium riders. Fat is not very nutrient-dense. Those nine calories per gram displace proteins and carbohydrates and are rarely high in vitamins or minerals. While fats play an important role in hormone production and nerve cell function, especially in children and young adults, the U.S. national average of 40%+ of calories derived from fat is well over the recommended 25 to 35%.
Carbohydrates are the tiger in every cyclist's tank. They are also the best source of fiber. The optimum percentage of calories derived from carbohydrates is 50% to 60%. The more complex these carbos are the better. Whole grain breads, pastas, brown rice, and vegetables like potatoes, peas and corn are the best sources of quality carbohydrates.
One way of assuring good blood sugar levels during a race is by carbohydrate supercompensation or "carbo loading". By first depleting the body's glycogen stores with a low carbohydrate diet, tricking it body into storing more glycogen than normal, and then loading it with primarily complex carbohydrates total glycogen is increased, at least in theory. While there is a proven benefit to carbo-loading for single day events lasting over two hours, but there are also significant drawbacks. The depletion phase is physiologically stressful. An elite athlete must train easier during the depletion phase. The carbo-loaded athlete will also weigh more due to the large quantities of water stored with each gram of glycogen. This water will help with hydration later in the race but could be a hindrance in the event of an intense early effort.
Drinking before a race or ride is just as important as drinking during the ride. It is a good idea to drink a large glass of water or juice (unsweetened, of course) regularly, whether you're thirsty or not and, if you drink coffee or tea with breakfast, another glass to counteract caffeine's dehydrating effect.
After a long ride many cyclists notice a significant weight loss. Ninety-five% of this lost weight is water. To recover quickly replace the lost fluid by drinking two cups of water every half hour for every pound lost. Do not rely on your sense of thirst. Delaying the rehydration will also delay recovery.
Amazingly, lots of (non-elite) athletes train before breakfast or skip breakfast altogether. Skipping the morning meal is an unproductive habit which should be "unlearned" at the earliest possible opportunity.
Think about it: the average human uses more than six hundred calories during any twelve hour period (including sleep) just for basal metabolism; a recovering athlete uses considerably more. Beginning a workout hundreds of calories in glycogen debt does not lead to a productive workout. Why be a slave to a bad habit? Get used to eating breakfast. Start with a glass of juice; when you're comfortable with that add some toast or oatmeal, eggs (the ideal breakfast food) or even a breakfast bar. After a few days of eating breakfast any discomfort should go away and those morning workouts will improve noticeably.
The only way to really be sure you're eating well is to do a dietary analysis. Write down your standard diet for three days. Specify the quantities and descriptions of all meals and snacks. Then: 1) Check out a copy of the "Nutritive Values of American Foods" and look up the nutritive values of what you ate. Or, 2) Take your diet list to a Registered Dietitian for a detailed computer analysis. This is about the most useful nutritional information an athlete can get.
For the definitive word on nutrition go to the nearest college bookstore and pick up a copy of "Nutrition for Living" (Christian, J., Benjamin/Cummings, 1985). This volume serves as the reference text for most nutrition courses. It is well written and informative without the biases and inaccuracies often found in popular books.
(C) 1989, Roger Marquis (www.roble.net/marquis), See also VeloNews, 2-91