What you eat before and during a major competition can affect your performance enough to give you an edge over your peers. The days of "carbohydrate loading" are gone, but now athletes are being lured to try the LCHF fad — a low-carbohydrate, high-fat diet. A low-carbohydrate diet is unlikely to improve your performance in endurance events and can actually hinder you in sprint events. See my report on the latest LCHF research, Low Carbohydrate Diets Harm Athletic Performance..
What to Eat the Week Before Competition
Eat your regular diet right up to your pre-race meal. Do not take in excess carbohydrates as you can store only a small amount of sugar in your muscles and liver. The extra carbohydrates from "carbohydrate loading" are all turned into fat and the extra weight will just slow you down. Extra fat in muscles reduces the amount of sugar they can store. In 1973 I wrote an article that was published in the Journal of the American Medical Association, reporting that excessive carbohydrate loading can cause heart attacks in marathon runners (JAMA, March 26, 1973;223(13):1511-1512). Competitive athletes will store their maximal amount of sugar just by cutting back on their training workloads for a couple of days.
The Night Before Competition
Athletes used to foolishly "carbohydrate load" with pasta parties the night before a race. On the next morning, they would often pay the price with constipation caused by the huge amount of low-fiber food. The ideal meal on the night before competition should be full of fiber, because high-fiber foods are bulky and hold water, helping to keep food moving through the intestinal tract. Instead of bread and pasta, eat vegetable salads, whole grains, beans, seeds and nuts. Just make sure that you get up early enough on the day of competition to empty your bowels. Meat, chicken, fish and other high-protein, high-fat foods are also perfectly good sources of energy.
The Pre-Competition Meal
Eat your pre-competition meal three to four hours before your event. Most foods are fine as long as your stomach is not full when you start your competition. Most athletes eat whatever they normally eat for breakfast. Some athletes eat fruit, eggs and toast, while others prefer a cooked or dry cereal. Avoid sugar and sugar-added foods as they can cause a high rise in blood sugar followed by a high rise in insulin. When you start a competition with high blood levels of insulin, the combination of contracting muscles rapidly drawing sugar from your bloodstream plus the high insulin levels can cause low blood sugar that will make you feel very tired.
Twenty Minutes or Less Before Your Event
Some athletes take a sugared drink with caffeine just before they begin their event. The sugar will be used to fuel your muscles and the caffeine helps the sugar to be absorbed faster and moves it more rapidly into muscles. Contracting muscles draw sugar rapidly from the bloodstream without needing insulin, so taking sugar just before or during competition usually does not result in the high rise in blood sugar levels that causes your pancreas to release large amounts of insulin, which can drive you into exhaustion from low blood sugar.
During an Event Lasting Longer than an Hour
Taking extra sugar during a competition lasting more than an hour is far more important than anything you eat or drink before your event. How fast and intensely you can exercise in events requiring endurance depends on how quickly you can get sugar into muscles during exercise. The energy for your brain comes almost exclusively from the sugar in your bloodstream. When blood sugar levels drop, so do brain levels and you feel tired and have difficulty coordinating your muscles. You can markedly improve performance in endurance sports lasting longer than an hour by starting to eat and drink soon after you start exercising.
Another reason why you have to take sugar during intense exercise is that there is only enough sugar in your bloodstream to last three minutes at rest. To maintain blood sugar levels, your liver constantly releases sugar into your bloodstream. There is only enough sugar in your liver to last about twelve hours at rest and far less than that when you exercise. When muscles run out of their stored sugar supply, it hurts to exercise and the muscles become difficult to control.
Don't wait to feel hungry. Hunger during exercise is a very late sign of not getting enough calories. By the time you feel hungry, your body will be so depleted of sugar that you will have to slow down and eat large amounts of carbohydrate-rich food just to restore your sugar supplies.
What to Eat and Drink During Your Event
All carbohydrates are single sugars or sugars bound together in twos up to thousands (starches) and millions (fiber). Before any carbohydrate can be absorbed into your bloodstream, it must first be broken down into single sugars. Human intestines do not permit combination sugars to pass into the bloodstream. The quickest way to maintain the blood sugar levels you need for endurance during prolonged vigorous exercise is to eat sugar-containing foods or drinks.
Caffeine taken during exercise can increase endurance (Medicine & Science in Sports & Exercise, July 2010) by increasing the absorption of sugar from your intestines and by increasing the uptake of sugar by your exercising muscles by as much as 26 percent (Journal of Applied Physiology, June 2006). Caffeine is found in coffee, tea, many sodas and chocolate. CAUTION! Take caffeinated sugared drinks only when you exercise. Taking caffeine and sugar when you are not exercising can double your rise in blood sugar (Journal of Caffeine Research, April 16, 2011). Repeated and prolonged high rises in blood sugar can cause all the horrible side effects of diabetes: heart attacks, strokes. blindness, deafness and so forth.
Salt: The only mineral that you need to take during prolonged exercise is sodium, found in ordinary table salt. Potassium, calcium or magnesium deficiencies do not occur in healthy athletes (Medicine & Science in Sport & Exercise, October 1999). Just about everyone agrees that you need to take in drinks or foods containing extra salt during athletic competitions lasting more than three hours, particularly in hot weather. Not everyone agrees that athletes need to take in extra salt at rest. If you don't take salt and fluids during extended exercise in hot weather, you will tire earlier and increase your risk for heat stroke, dehydration and cramps. You can drink special electrolyte drinks if you wish, or eat salted foods such as nuts or potato chips along with any fluids during competition.