Carbohydrate is one of the most important nutrients to athletic performance. Carbohydrate plays the major role in supplying your brain and body with power. The body cannot supply enough carbohydrate on its own and therefore it needs to come from foods. Exercising with low levels of carbohydrate leads to fatigue. Carbohydrates are the ideal fuel for muscular work.
Carbohydrate is stored as glycogen, which is stored in the muscles and liver. Liver glycogen is used to maintain blood sugar, which, in turn, fuels the brain, nervous system and other cells. Optimal blood sugar levels are important for clear brain function and therefore critical to sharp, high speed mental performance. Low blood sugar results in weakness and fatigue. Muscle glycogen fuels muscle cells during exercise. Muscle glycogen and fat supply energy during endurance activities. Maximizing glycogen stores is one of the primary goals of sports nutrition.
When exercising hard there is a continual loss of glycogen from the active skeletal muscle during the prolonged exercise. When the glycogen stores become depleted the athlete will not be able to exercise intensely and will experience fatigue. A gradual decline in muscle glycogen is related to the chronic fatigue often experienced by athletes during repetitive strenuous training conditions. Chronic fatigue often limits an athlete’s ability to comply with a progressive training program and subsequently to compete at maximal potential. If you do not eat enough carbohydrates to refill the stores that are depleted in each workout, you may not have enough carbohydrates available during ensuing workouts. Therefore, consuming carbohydrates during endurance exercise can postpone fatigue and prolong peak performance.
Diet and endurance training influence the amount ofglycogen stored in muscle and the time it takes to exhaustion. A high carbohydrate diet can raise the initial muscle glycogen concentration and thus there will be a greater time to exhaustion. Diet provides the body with the needed fuels, while training promotes muscles to store more carbohydrate and help improve the body’s utilization of fuel. More muscle glycogen will help increase endurance. An individual that is more fit uses less glycogen, is better able to conserve the limited glycogen stores in the body, and utilizes more fat as a fuel source during endurance events.
Athletes who follow a high-carbohydrate diet can maintain high-intensity exercise for a longer period than those on a lower-carbohydrate diet. There is substantial evidence for a benefit of carbohydrate intake for the performance of brief, high power events if the competitor has been consuming a reduced energy diet.
Total carbohydrates are made up of simple sugars, complex carbohydrates, and fiber.
Simple carbohydrates are commonly known as sugars. Sources of simple carbohydrates include table sugar, candies and other sweets, sodas and bakery goods. These foods provide empty calories, i.e., calories that supply no vitamins and minerals and should therefore be minimized.
Complex carbohydrates include all the complex starches and fiber, such as those found in grains, cereals, breads and starchy vegetables like potatoes, corn, peas and beans. Milk, fruit and vegetables also contain carbohydrate.
Complex carbohydrates contain many essential nutrients and are the body’s most effective source of energy to the athlete. Complex carbohydrates increase glycogen stores more efficiently than sugars, or simple carbohydrates.
Complex carbohydrates are ideal because they are quickly digested and absorbed into the bloodstream, leaving the stomach quickly so there is less chance of indigestion and nausea during the event.
Carbohydrates should make up the largest portion of the athlete’s diet. Research suggests that to maintain adequate carbohydrate stores during heavy training, carbohydrate intake should range from 7-10 grams/kg of body weight/day or 55-70% carbohydrate.
Athletes who train exhaustively on successive days, or who compete in more prolonged endurance events, would benefit from a diet that contains 65% to 70% of total calories from carbohydrates.
Fats, like carbohydrates, are used by the body for fuel and are essential for the absorption of certain vitamins. The most important role of fat is to spare carbohydrates (which are in limited supply) in exercise of long duration and low intensity.
Fat is a valuable metabolic fuel for muscle activity. Endurance training significantly increases the ability of muscle to utilize fat. During aerobic exercise, fat serves as the preferred fuel source for muscle activity, however, this relationship is not necessarily enhanced by increasing the dietary intake of fat. The endogenous body fat stores are more than adequate to meet these needs. Even the leanest athletes have sufficient fat storage to meet the metabolic demands of strenuous exercise.
Consuming a high-fat diet will result in a larger proportion of fats used during exercise, but this limits the amount of carbohydrate storage, which ultimately limits endurance.
Therefore high dietary fat intakes should be avoided. Also too much fat can lead to heart disease, obesity, cancer and other health problems. Fat intake for athletes, as well as healthy adults, should comprise less than 30% of total calories. Fats in the diet may be of animal or vegetable origin. Selecting lean meats, nonfat or low fat dairy products and limiting added fats such as butter, margarine, salad dressing, cream sauces, gravies and fried foods will help you achieve this goal.

Protein and Amino Acids
There is a general misunderstanding about the protein needs of athletes. Many believe that large quantities of protein foods are necessary to enhance muscle growth. Training techniques and genetics are the critical determinants of muscle size. Extra protein in the diet beyond what your body demands for rebuilding and repair doesn’t go to make extra muscle. Protein can’t be stored for later use, if the athletes body gets more protein than it needs, the extra is broken down and stored as fat or used as energy.
High protein intakes have never been shown to be uniquely beneficial to athletes.
Intakes of protein > 15% of total calories cannot be justified on a scientific basis. For an individual consuming 4000 calories per day, 15% of calories represent 150 grams of protein or 2 grams/kg body weight for 70-kg male (note RDA is 0.8 grams/kg of body weight/day). This almost exceeds the requirement by 270%.
Intakes above 15% or 2 grams/kg of body weight are either burned for energy to support activity or are converted to fat.
In addition, these processes result in residual nitrogen, which must be discarded through the urine as urea and ketones. This step requires the loss of water, which increases the athlete’s chance of dehydration. Excessive protein intake (5 times the RDA) can also cause a loss of bone calcium and can also put strain on the liver and kidneys.
Protein is the toughest nutrient to digest. Your body expends a lot of energy just breaking down high protein foods. Therefore high protein foods should be avoided before training.
Contrary to popular opinion, muscle size is not dependent on protein intake. If daily minimum intakes are met, muscle size will be dictated by the specific training demands and of course genetic potential.
Protein can be supplied from animal food sources, such as lean meat, poultry, fish, eggs, milk, and cheese, or vegetable food sources such as dried beans and peas, peanut butter, nuts, seeds, and tofu. Breads, cereals and vegetables contribute small amounts of protein in the diet. Plant protein from vegetable sources is usually low in one or more of the nine essential amino acids. Vegetable protein sources, in combination, can complement one another to provide a high-quality protein.
Of all the physiological factors that can cause early fatigue during exercise, dehydration is arguably the most important. Dehydration is a common occurrence, even during exercise in the cold. Dehydration decreases performance, impairs cardiovascular function that can impair physical performance, and pose serious health problems.
Athletes can lose a large amount of fluid when exercising. An athlete can become dehydrated in as little as 30 minutes.
Dehydration occurs when fluid (sweat) loss exceeds 1% of body weight (800 ml in the case of an 80-kg male). Work capacity and temperature control can be impaired with a loss of as little as 2% of body weight and can cause a 5-10% drop in performance. A 1/10th-temperature change can decrease performance.
During any form of exercise, working muscles produces heat, and body temperature rises. Getting rid of this heat requires fluid evaporation from the skin (sweating) which cools the body. When fluid evaporates from the skin the body therefore losses valuable water (as high as 1-2 quarts/hour) during heavy exercise. When the athlete fails to ingest enough fluid and dehydration becomes sufficiently severe, sweating decreases in an attempt to conserve body water. As a result, blood thickens, heart rate increases and body temperature rises and you get fatigue, headache, nausea, chills, stomach discomfort and increasing the chance of heat cramps, exhaustion, or stroke.
Recent research illustrates that maintaining normal or near hydration during exercise maintains cardiovascular and thermoregulatory responses and improves exercise performance. It is always the athlete’s best interest to prevent unnecessary increases in core temp that will ultimately lead to premature fatigue.
As you exercise, be alert for these conditions. They’ll increase your loss of fluid through sweat, which could make your body become dehydrated faster.
Temperature: The higher the temperature, the greater your sweat losses.
Intensity: The harder you work out, the greater your sweat losses.
Body size: The larger the athlete, the greater the sweat losses. Males generally sweat more than females.
Duration: The longer the workout, the greater your fluid losses.
Fitness: Well-trained athletes sweat more. And they start sweating at a lower body temperature. Why? The function of sweating is to cool the body. The well-trained athlete cools his or her body more efficiently than an untrained person.
Most active people have experienced dehydration and probably haven’t been aware of it. Exercise blunts the thirst mechanism and cannot rely on thirst as an indicator of dehydration. Providing adequate fluid intake before, during and after exercise can prevent dehydration. Fluid replacement practices should be designed to match fluid intake and sweat loss. This approach will require sports competitors to ingest more fluid, often more that they are accustomed to drinking.
The rate of fluid replacement should match rate of sweating (at least 80%)
Each pound of weight loss corresponds to 450 ml (15 oz) of dehydration (8 oz = 1 cup)
Plain, cool water (5° to 10°C; 40° to 50°F) is an effective fluid replacement, and it is the most readily available and least costly alternative. Drink plain water before or during activities lasting 60 minutes or less.
To read some very good reasons to drink more water click here
Electrolytes (sodium, potassium, chloride, and magnesium) are lost in sweat, but the loss of water is considerably greater. However, in sport or training that requires more than 1 hour of continuous effort, a carbohydrate-electrolyte solution should be provided to improve performance.
Guidelines for proper hydration
Learn about dangers/disadvantages of dehydration
Become aware of sweat losses (weigh before and after exercise)
Drink to a plan
Drink early
Make fluid available
Practice during training