Nutrition For Exercise & Sports Performance
Anaerobic or Lactic Acid Pathway
Anaerobic pathway supplies energy for an effort lasting between 60-120 seconds as in a 440-yard sprint or many other sprint swimming events. This pathway is used to supply ATP for more than 8 seconds of activity. Energy is released from glucose in the absence of oxygen.
Oxygen is required for a continuous supply of energy when the muscle activity is longer than 90 to 120 seconds. Here glucose is used far more efficiently supplying almost 18 to 19 times more ATP.
Any physical activity uses energy from ATP through anaerobic pathway. If this activity prolongs, the aerobic pathway becomes the primary source of fuel.
Fuel for Contracting Muscles
Carbohydrates, proteins and fats are all possible fuel sources for muscle contraction. But the fuel source used depends on factors such as intensity and duration of exercise, fitness level of the individual, gender of the person and the dietary intake.
How long you are involved in an exercise determines the energy substrate used during the workout period. Fat can supply up to 60% to 70% of the energy needed for high tenacity events lasting 6 to 10 hours. Hence fat is always the first suggested fuel for workout when the duration of the exercise is longer. Carbohydrates are essential in the energy pathways as fats cannot be metabolized in their absence.
Effect Of Training
An athlete’s body type and exercise intensity determine the length of time for which an athlete can oxidize fatty acids as a fuel source. Training improves cardiovascular supply of oxygen and the number of mitochondria and enzymes involved in aerobic synthesis of ATP, thus resulting in increased fatty acid metabolism. Training also results in a lower blood lactate and catecholamine levels, lower net muscle glycogen breakdown and lower respiratory exchange ratio (RER).
Nutritional Requirement Of Exercise
Proper intake of calories is the foundation to strike the right balance between energy expenditure and overall health maintenance. Calorific needs, nutrients and energy differ depending on the individual’s height, weight, age, sex and metabolic rate. Also the intensity, frequency, type and duration of workout impact the nutrient needs. The calorie needs of different groups of individuals are tabulated below:
Every category of individuals has restrictions and different environments which affect their overall nutrition and activity performance. Hence sports bars, drinks and convenience foods are consumed along with whole foods to meet the daily energy needs. Also dieticians need to be accommodative and flexible to plan the meal structure according to the athlete’s lifestyle for maximized output.
Ready-to-eat, easy-to-consume and easy-to-carry meal-replacement powders (MRPs), ready-to-drink supplements (RTDs), energy bars and energy gels are all convenient supplements and these represent almost 50% to 70% of the industry’s sales. These products contain between 33% to 100% of the recommended daily allowances (RDAs) for vitamins and minerals, provide the needed fats, proteins and carbohydrates and are simply the best choice for athletes, for people who travel often and for individuals participating in track and field events, swimming, diving or gymnastics. But one must be cautious to not replace daily dietary intake completely with these foods as they may contain increased levels of sugar, fats and proteins along with banned substances such as caffeine, ephedra and other botanicals.
We often find athletes increasing or decreasing their weight to maximize performance. They alter their energy intake levels and push too hard to achieve a light-weight body. This can be commonly seen among female athletes participating in dancing or gymnastic event. Such drastic weight changes may ruin normal growth and result in eating disorders, delayed menarche and osteoporosis. Body fat should be the determining factor for goal weight of an individual. Weight gain or weight loss must be a gradual process with a weight loss between .5-1kg every week over several weeks and weight gain between 0.2-0.4 kg/week. Weight gain should constitute muscle gain over fat gain through strength training programs and fat intake of not more than 30% of kilocalories of the total calories consumed and protein intake of 1 to 1.5 g/kg of body weight.
Individuals taking up regular fitness programs can comfortably meet their macronutrient needs by consuming a diet of 45% to 55% of calories from carbohydrates, 10% to 15% from protein and 25% to 35% from fat. Athletes involved in moderate-to-high volume training require greater amounts of carbohydrates and protein to meet their macronutrient needs. The recommendations vary greatly according to the individual’s body type, sports event in which they are participating and gender.
Carbohydrates requirements go parallel with an athlete’s daily total energy expenditure, type of sport, gender and environmental conditions.
Carbohydrate Intake Before, During and After Exercise
Carbohydrate consumption before exercise helps to prevent hunger during exercise and maintain optimal blood glucose levels for the exercising muscle. The preevent meal should be:
Carbohydrates are consumed in between endurance exercise if the workout lasts for more than an hour to maintain blood glucose and boost output levels. The state of food consumed differs according to the athlete’s desire. Some athletes may prefer a sports drink while others may go for an energy bar or gel along with plain water. Around 26g to 30g of carbohydrates in the form of sports drink can be consumed every 30 min.
Carbohydrate Intake After Exercise
The muscle glycogen used during exercise must be replenished after workout. Maximum replenishment rate can be achieved when large quantities of carbohydrates (1-1.85 g/kg/hr) are consumed every 15-60 minutes for 5 hours after exercise. Supplementing this with 5 to 9g of protein for every 100g of carbohydrate consumed can elevate glycogen resynthesis rate. Majority of the athletes prefer to consume carbs in the form of liquids rather than eating them or to consume ready-to-eat foods such as bananas, oranges, melon or fruit pops.
Protein : RDA protein recommendations include
While inadequate protein intake can end in training intolerance, muscle wasting and retarded recovery consuming higher than recommended levels of protein should also be avoided. This can lead to improper training and competing at peak levels and also result in dieresis or dehydration.
Fat supplies almost twice the calories (9 kcal/kg) by weight as proteins (4 kcal/g) or carbohydrates (4 kcal/kg). Fat is the major source of fuel for most of the light- to moderate-intensity exercises. Though fat is an important fuel for longer aerobic exercises athletes should not try to overeat fat unless their consumption level constitutes lesser than 15% of calories from fat. When a person tends to consume a high-fat diet care should be taken to consume fewer calories from carbohydrates. But it is always recommended to follow a high-carbs, low-fat diet to avoid health-related problems such as obesity, cardiovascular diseases, diabetes and some types of cancer. Fats should contribute to not more than 20% to 30% of the total calories consumed.
Vitamins and Minerals
Many researchers have concluded that unless an athlete is deficient in a nutrient, like vitamins and minerals, supplementations do not boost performance. But many nutrients such as folate, zinc, vitamin B and calcium are of concern in athletes. This is due to their training schedules, infrequent nutrient-dense meals and low calorie intakes due to weight restrictions in certain events and games (gymnastics or dancing).
B vitamins assist in energy cycles for increased energy metabolism. Wrestlers, gymnasts and rowers, who consume low-calorie diets continuously, lack B vitamins and supplementations aid to meet RDA levels. Vegetarian athletes could lack vitamin B12 as animal foods are their only sources and supplements are mandatory for such athletes. Athletes whose fruits and vegetables consumption is low lack in folate and hence supplementations along with wheat, grain and fortified products rich in folate are suggested.
A diet high in antioxidants or supplements for the same can be proposed to antioxidant-deficient individuals. Fruits and vegetables are good sources of antioxidants.
Vitamins C and E
Vitamin C helps to improve the health and physical performance of athletes. Vitamin E helps to improve performance, provides protection against exercise-induced oxidative injury and enhances immune response. Vitamin E supplementation of 200 to 450 IU daily gives protection against oxidative injury.
Lack of iron even without anemia can lead to decrease in exercise performance. Low iron content is common among male adolescents, female athlete with heavy menstrual losses, athletes consuming energy-restricted diets and those training heavily in hot climate with heavy sweating. Iron supplementation and oral iron therapy are helpful in athletes lacking iron but not anemic.
Female athletes, who have interrupted menstrual function, are at a high risk of osteoporosis. Female athlete triad is becoming popular among women athletes. Symptoms include estrogen deficiency, amenorrhea, disordered eating, low body fat and loss of bone mass. Treatment for this includes estrogen replacement therapy, weight gain and reduced training. It is generally prescribed for an increased intake of calcium and magnesium in female athletes irrespective of the menstrual history. Good sources of calcium include low-fat and nonfat dairy products, calcium-fortified fruit juices, soy milk and tofu. Amenorrheic athletes are recommended an intake of 1500 mg of calcium which can be met only with a daily supplementation of calcium and vitamin D along with diet.
Drinking fluids is indispensable to regulate body temperature. Exercise produces heat and this must be reduced to avoid heat stress. Body shape, environmental conditions and physical activity determine the fluid intake needs of a person. DRI recommendations suggest water intake of 3.7 L/day in males and 2.7 L/day in females. Almost 20% of water comes from the food we consume and the remaining 80% must be consumed in the form of plain water, juice, coffee, tea, milk, sports drink and soup. Fluid intake increases greatly for individuals training in hot environments and can go up to 10 L/day.
It is recommended to replenish for the lost fluids immediately as athletes can tolerate a maximum loss of 2% of body weight. But even such a loss cannot be tolerated in hot temperatures and can disrupt performance. Rather than drinking plain water it is recommended to include sodium in fluid replacement solutions as plain water without any sodium intake can result in hyponatremia. This condition is relevant in individuals whose sodium levels fall below 130mEq/L and is indicated by symptoms such as lethargy, seizures or loss of consciousness. This can be treated by drinking sodium-containing fluids to provide the required 680mg of sodium per hour.
Potassium is an important electrolyte, similar to sodium, which helps to maintain body fluids. A potassium loss of 32 to 48 mEq/day is very meager and can be easily substituted by diet.
The rate at which any fluid is absorbed depends on many factors like the amount, type and temperature of the fluid consumed and the rate of gastric emptying.
Ergogenic aids include anything that is used to improve exercise performance capacity and training adaptations such as training techniques, alternative nutrition practices or a mechanical device. Dietary supplements are the most commonly used ergogenic aid. Research proves that 50% to 98.6% university athletes use some kind of supplements as ergogenic aids. Though many athletes believe that using these aids can boost their performance the reality is quite different. Many of these supplements do no help to improve performance but rather prove to affect the health and performance of the athletes in a negative way when consumed continuously.
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Dietitian & Nutritionist Dr. Nafeesa Imteyaz.