Athletic Performance
The right diet is the key to managing many diseases and to improving general quality of life. For this condition, scientific research has found benefit in the following healthy eating tips.
Low-Glycemic Index Diet
The glycemic index is a measure of a food’s ability to raise blood sugar levels. Before exercise, low-GI foods can be beneficial, while high-GI foods can quickly restore sugar stores after exercise.Low-Glycemic Index DietThe glycemic index (GI) is a measure of the ability of a food to raise blood sugar levels after it is eaten. Attention to the GI of carbohydrate sources may be helpful for increasing sports performance. Within one hour before exercise, consuming low GI carbohydrates (such as most fruits, pasta, legumes, or rice) provides carbohydrate without triggering a rapid rise in insulin that could result in hypoglycemia and prevent release of energy sources from fat cells.161 Some controlled studies of cycling endurance have found that eating a pre-exercise meal of low-GI foods (lentils, rolled oats, or a combination of low GI foods) is more effective than consuming high-GI foods (potatoes, puffed rice, or a combination of high GI foods),162,163,164 but most studies have found no significant advantage of low GI foods or fructose (a low-GI sugar) compared with other carbohydrate sources in a pre-exercise meal. 165,166,167,168,169,170,171,172 After exercise, on the other hand, high-GI foods and beverages may be most helpful for quickly restoring depleted glycogen stores.173
Fats
Some athletes have found success following a high-fat diet for a number of days and then briefly eating a high-carbohydrate diet prior to an endurance event.FatsSome athletes have speculated that consuming a high-fat diet for two or more weeks prior to endurance competition might cause the body to shift its fuel utilization toward more abundant fat stores ("fat adaptation").174 However, neither short-term nor long-term use of high-fat diets has been found to improve endurance performance compared with high-carbohydrate diets, and may even be detrimental due to depletion of glycogen stores.175,176
Following a high-fat diet with at least 24 hours of high carbohydrate intake has been suggested as a way to achieve fat adaptation while restoring glycogen levels before endurance competition.177,178 While this concept is supported by physiological studies on athletes, no actual performance enhancement was shown when athletes were tested in competitive situations after a five- to six-day high-fat diet followed by 24 hours of high carbohydrate intake.179,180,181 However, one controlled study found a small, significant benefit of ten days of high fat intake followed by three days of high carbohydrate intake.182
Water and Sports Drinks
Loss of water and electrolytes due to sweating during exercise can result in decreased performance and other problems, so remember to drink plenty of water and electrolyte-balancing sports drinks prior to, during, and after exercise.Water and Sports DrinksWater is the most abundant substance in the human body and is essential for normal physiological function. Water loss due to sweating during exercise can result in decreased performance and other problems. The American College of Sports Medicine's recommenations for fluid consumption by exercisers were updated in 2007.183 Fluids should be consumed prior to, during, and after exercise, especially when extreme conditions of climate, exercise intensity, and exercise duration exist. Enough fluids should be consumed up to two hours before exercise begins to produce urine that is not too dark or concentrated. The amount of fluid that should be consumed during exercise will vary depending on many factors, including personal sweating rate, climate, and type and duration of exercise. Exercisers should generally drink to satisfy their thirst, and should also monitor changes in their body weight during exercise. If weight loss approaches 2% of body weight, then fluid consumption has been inadequate to prevent dehydration. After exercise, enough additional fluid should be consumed to equal 150% of weight lost (24 ounces of fluid for each pound of weight loss). Some individuals may experience an increase in body weight during exercise; this can indicate that too much fluid has been consumed, which can lead to a potentially dangerous condition called hyponatremia (low blood sodium levels) even if electrolyte-containing sports drinks are used. A professional knowledgeable in sports medicine can help formulate an individualized plan for fluid consumption during exercise.
Flavored sports drinks containing electrolytes are not necessary for fluid replacement during or after brief periods of exercise, but they may be more effective in encouraging the athlete to drink frequently and in larger amounts when needed.184 Consuming fluids along with meals or salty snacks before and after exercise will also encourage sufficient fluid intake and may improve fluid retention in the body.183
Complex Carbohydrates
Carbohydrates may be the most important nutrient for sports performance, as they are the most efficient fuel and can be stored in the muscle and liver as readily available energy.Complex CarbohydratesCarbohydrates are the most efficient fuel for energy production and can also be stored as glycogen in muscle and liver, functioning as a readily available energy source for prolonged, strenuous exercise. For these reasons, carbohydrates may be the most important nutrient for sports performance.185 Depending on training intensity and duration, athletes require up to 4.5 grams of carbohydrates per day per pound of body weight or 60 to 70% of total dietary calories from carbohydrates, whichever is greater.186,187 Emphasizing grains, starchy vegetables, fruits, low-fat dairy products, and carbohydrate-replacement beverages, along with reducing intake of fatty foods, results in a relatively high-carbohydrate diet.
Carbohydrate beverages should be consumed during endurance training or competition (30 to 70 grams of carbohydrate per hour) to help prevent carbohydrate depletion that might otherwise occur near the end of the exercise period. Standard sport drinks containing 6 to 8% carbohydrates can be used during exercise to support both carbohydrate and fluid needs, but these should not contain large amounts of fructose, which can cause gastrointestinal distress.188 At the end of endurance exercise, body carbohydrate stores must be replaced to prepare for the next session. This replacement can be achieved most rapidly if 40 to 60 grams of carbohydrate are consumed right after exercise, repeating this intake every hour for at least five hours after the event.189 High-density carbohydrate beverages containing 20 to 25% carbohydrate are useful for immediate post-exercise repletion.
Adding protein to carbohydrate intake immediately after exercise may be helpful for improving recovery of glycogen (carbohydrate) stores after exercise according to some,190,191,192 though not all,193,194,195,196,197 controlled studies. It appears that adding protein during the post-exercise period is not necessary when carbohydrate intake is high enough (about 0.55 grams per pound of body weight).198
Carbohydrate loading, or “super-compensation,” is a pre-event strategy that improves performance for some endurance athletes.199,187 Carbohydrate-loading can be achieved by consuming a 70% carbohydrate diet (or 4.5 grams per pound of body weight) for three to five days before competition, while gradually reducing training time, and ending with a day of no training while continuing the diet until the event date.
Protein
Athletes require more protein than people who are not exercising vigorously, but supplementing is not necessary as long as the diet contains at least 12 to 15% of calories as protein.ProteinProtein requirements are often higher for both strength and endurance athletes than for people who are not exercising vigorously; however, the increased food intake needed to supply necessary calories and carbohydrates also supplies extra protein. As long as the diet contains at least 12 to 15% of calories as protein, or up to 0.75 grams per day per pound of body weight, protein supplements are neither necessary, nor likely to be of benefit.200,201 Concerns have been raised that the very high-protein diets sometimes used by body builders could put stress on the kidneys, potentially increasing the risk of kidney disease later in life. A preliminary study of male athletes consuming at least 2.77 grams per pound of body weight per day showed no evidence of kidney impairment; however, the study was limited to one month, and evidence of long-term kidney problems associated with chronic protein loading were not examined.202
Preliminary studies have suggested that increased protein intake may have biological effects that could improve muscle growth resulting from strength training, especially if liquid supplements (typically containing at least 6 grams of protein or amino acids in addition to varying amounts of carbohydrate) are taken either immediately after exercise or just before exercise.203,204,205,206,207,208,209 However, controlled studies have found no advantage of protein supplementation (up to about 100 grams per day or about 14 grams immediately following exercise) for improving strength or body composition as long as the diet already supplies typical amounts of protein and calories.210,211,212
High-Calorie
Athletes have different calorie requirements, depending on the intensity of their training and performance. Calorie restriction can have many negative effects, so be sure to get enough fuel through calories.High-CalorieCalorie requirements for athletes depend on the intensity of their training and performance. The athlete who trains to exhaustion on a daily basis needs more fuel than one who performs a milder regimen two or three times per week. Calorie requirements can be as much as 23 to 39 calories per pound of body weight per day for the training athlete who exercises vigorously for several hours per day.213,214 Many athletes compete in sports having weight categories (such as wrestling and boxing), sports that favor small body size (such as gymnastics and horse racing), or sports that may require a specific socially accepted body shape (such as figure skating). These athletes may feel pressured to restrict calories to extreme degrees to gain a competitive edge.215 Excessive calorie restriction can result in chronic fatigue, sleep disturbances, reduced performance, impaired ability for intensive training, and increased vulnerability to injury.216