Healthy Nutritional Diet For Athletes - Sports Diet
Sports performance has become very competitive. Though good nutrition is essential for optimal physical performance, it has not been well-studied. The usual diet chosen for athletes has no scientific basis, but owes much to the confidence the athlete feels in the trainer or nutritionist. Sufficient calories should be provided; fluid and electrolyte replacement should be adequate. If ingestion of certain foods provides a psychological crutch, they must be given for the psychological advantage. Eating before competition should be judicious to avoid retention of undigested food in the gut during competition.
Most athletes say they are aware of the importance of good nutrition, but when they sit down to eat, their patterns of food intake are often considerably less than optimal. One key problem is that athletes often take in less energy than they really need to support strenuous training. Another is that they simply don't ingest enough carbohydrate.
The liver contains about 150 g glycogen (carbohydrate), and skeletal muscles about 400-500 g; therefore, glycogen cannot function as a long term fuel store.
During fasting, after glycogen is depleted, blood sugar is maintained for 12-16 hours by formation of glucose (gluconeogenesis) from free fatty acids (FFA). (Glucose is also formed from protein and fat in the immediate post-feeding period) Within 2-3 days of starvation , the muscle and brain adapt by using ketoacids as fuel.
At rest, a healthy person derives 85%-90% energy from FF A, about 10% from glucose, and 1%-2% from amino acids. During strenuous exercise, glucose utilization may be increased 3045-fold above the resting state. Both liver and muscle glycogen stores are soon depleted, and fatigue occurs. The principal source of energy, then, is FF A released from the fat depot. With training, FF A to increasingly utilized to supply energy. Mobilization of lipid as a source of energy is not rapid enough; the exercise may then proceed at a rate permitted by fatty acid oxidation.6
Hypoglycemia (blood sugar less than 45 mg per 100 ml; 2.5 mmol/1) occurs during strenuous exercise and results in an exaggerated rise in plasma epinephrine. However, trained athletes maintain a higher blood glucose level with greater dependence on fat as fuel. They have increased size and number of mitochondria in the muscles; fatty acids are utilized by these mitochondria to provide energy.
A sudden burst of exercise, such as a 100 meter swim, produces a marked rise in blood sodium and lactate levels; with less vigorous exercise, blood lactate rises without a corresponding rise in sodium.
Dietary Management of athletes
Carbohydrate is the major fuel for short exercise. It is utilized both aerobically and anaerobically. A significant carbohydrate supply before and during exercise ensures optimum work performance. Pre-exercise snack feeding has little effect. A carbohydrate-rich meal 2-3 hours prior to an exercise ensures filling the labile glycogen store. A high-carbohydrate diet should include complex carbohydrates (cereals, potato, etc.) rather than simple sugars (glucose, sucrose, etc.) Recent consumption of a carbohydrate-rich meal lowers plasma FF A levels and forces muscles to burn carbohydrate.
If muscle glycogen is exhausted with exercise and a protein-fat diet, the glycogen content of the muscle is reduced to 0.6%; this rises within 24 hours to 4.7% on a high-carbohydrate diet.
Increased muscle glycogen enhances the work period. In order to augment muscle glycogen for a competition lasting over 30-60 minutes, it is suggested that preparations start a week before. For the first three days the muscles should be exercised on a protein-fat diet; thereafter, a high-carbohydrate diet enhances the muscle glycogen store on the day of the competition.
Glycogen replacement is far more in the exercised muscle than in the non-exercised muscle.10 This was seen in bicycle experiments where one leg was utilized for exercise and the other leg rested. After exercise, a carbohydrate-rich diet was given for three days. The glycogen content of the exercised leg, which was initially depleted, increased to 120% within the first 24 hours, and up to 230% on the third day, whereas only a small increase occurred in the leg that was not exercised. Thus, three nutritional measures increase exercise endurance.
The large fat stores in the body can supply energy for several days. Factors that limit the use of fat are the rate of mobilization of fat (which is much slower than glycogen) and the efficiency of oxidation.
With sufficient oxygen supply, muscles utilize up to 66% fat for energy; but with heavy muscular exercise, involving anaerobic (lack of oxygen) process, a major energy source is carbohydrate; that increases the duration and efficiency of work.
A great deal of emphasis is put on high protein intake. Athletes engaged in strength and power events traditionally take a high-protein diet. An athlete taking normal combinations of foods (cereals, milk, etc.) and consuming 4000-5000 kcal (16.8-21 MJ) naturally ingests twice the amount of protein consumed by a sedentary man (20002500 calories; 8.4-10.5 MJ). Though protein should be supplied adequately (1-1.2 g/kg), there is no evidence that excess protein intake will increase protein synthesis. Thus, the advocated high-protein diet has only a psychological effect.
Fluid and Salts
The most dramatic failures in marathon running have been caused by dehydration. Even in temperate climate, the cumulative sweat loss during a marathon is 3--4 litres, with associated loss of electrolytes. The loss of fluids and electrolytes is much more in hot and humid climates. During a long-run, the water reserves are liberated from glycogen metabolism.
Water balance of long-distance runners is improved by drinking about 12 litre of fluid 15-30 minutes before a race. Later, water is taken at watering stations according to needs. Too little will cause dehydration, and excess, frequent urination. The recommended drink to replenish fluid and electrolytes is 1 litre water with glucose 25 g, 10 mmol/1 sodium and 5 mmol/1 potassium.
An athlete is supplied with 500 g carbohydrate. A traditional type of food intake will supply adequate amounts of protein, fat, carbohydrates, vitamins and minerals. There is no good evidence that specific supplements are necessary to improve performance. However, some women may require iron supplement. As with other aspects of nutrition, erroneous ideas are propagated by food companies for sales of dietary supplements.
Breakfast consists of cereals with dried fruit, porridge, toast, marmalade, honey, jam, and fruit juice. The mid-day meal and dinner may be with potatoes, rice, vegetables, meat, fish, bread or chapattis, and pulses. The athlete should be well-adjusted to the diet many days prior to the event.
Endurance running is defined as a regular physically-demanding exercise, including frequent sessions of one-and-a-half hours or more, where significant demands are made on body sources of energy.
The metabolic rate during running may be 15-20 times that in the resting state. For women engaged in sports, low body fat and bodyweight are important.
Slow jogging for 10 minutes a day consumes 2-3.5 MJ in a week. This may be better for personal morale than weight loss.
Cheating in Sports
Great ingenuity is used in adopting unfair and unethical means for competition. Increasing the red blood cell mass (erythrocythemia) enhances the oxygen-carrying capacity of blood. To induce this, competitors may go to a high altitude, or resort to the use of erythropoetin (hormone of the kidney that stimulates blood formation) injections. It can also be accomplished by the infusion of 400 ml of the patient's own packed red blood cells collected a few days earlier (autologous transfusion); this has been shown to effectively increase the performance capacity in a 10-kilometer track race.
Drugs that enhance the exercise capacity and athletic performance are called ergogenic drugs. Drugs which impair these are termed ergolytic drugs. Smokeless tobacco, cocaine, drugs to reduce blood pressure, and drugs used to increase urinary output (diuretics) are ergolytic.
These are synthetic male hormones that have greater anabolic than androgen effect. In conjunction with diet and training, they increase lean body mass and muscular strength. Anabolic steroids are used by athletes mainly for strength sports (weight-lifting, body-building, shot-putting, discus and javelin throwing); they have greater effect on women.
The use of anabolic steroids is a serious health problem. These drugs are administered orally, intramuscularly, or by intravenous injection; needle-sharing may spread AIDS. Adverse effects are many: beard growth in women, baldness, deepening of voice, decreased breast size, acne, blood-filled cavities (peliosis hepatis) and stagnation of bile (cholestasis) in the liver, benign and malignant tumors, sterility, testicular atrophy, and decreased libido. The risk of heart disease is also increased because of increased blood pressure and low-density lipoprotein (LDL) cholesterol, and decreased high-density lipoprotein (HDL) cholesterol. Premature closure of epiphysis and gynecomastia (enlarged breast in males) are other complications.
Female Athlete Triad
The triad includes an eating disorder, stopping of menstruation, and-osteoporosis. The eating disorder is a result of the misconception that there should not be any fat on the bodies of athletes. Many young women have loss of appetite. For osteoporosis, 1500 mg calcium daily is advised. We do not have adequate information about estrogen dosage or its safety.
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