II. Physiology: Nutrient Requirements

  1. Water is the most important nutrient for the athlete
  2. Carbohydrates (bulk of calorie intake for sports)
    1. Athlete requires 5-10 grams/kg/day
    2. Carbohydrates comprise 65-70% of daily calories
  3. Protein
    1. General population protein requirements
      1. Recommended Daily Allowance = 0.8 g/kg/day
    2. Protein requirements for athletes
      1. Athletes require 1.8 grams/kg/day
      2. Athletes protein intake and output
        1. Comprise 15-20% of total dietary calories
        2. Comprise 5-10% of caloric use during Exercise
      3. Excess protein does not benefit strength or mass
        1. Residual protein is lost in the urine
  4. Fats comprise 15-20% of an athletes total calories
    1. Not utilized until 20 minutes into Exercise
    2. Important for prolonged, low intensity Exercise
    3. Limit to unsaturated fat (e.g. vegetable or fish oil)

III. Management: High Carbohydrate diet

  1. Maximizes intensity and endurance of Exercise
  2. Maintains muscle glycogen
  3. Added to fluids for faster absorption
  4. Increase carbohydrate before Exercise (70% of calories)
    1. Start increase the day before
    2. Consume up to 2-5 hours before competition
    3. Liquid carbohydrate may be taken 60 minutes before
    4. Benefit appears to be regardless of Glycemic Index
  5. Avoid Reactive Hypoglycemia from Insulin surge
    1. Avoid carbohydrates within 60 minutes of Exercise
    2. Highest Hypoglycemia risk with high Glycemic Foods
      1. Glucose
      2. Sucrose
      3. Maltodextrin
    3. Low Glycemic Foods may not result in Insulin surge
  6. During endurance competitive event
    1. Consider carbohydrate intake during endurance event
    2. Several studies show performance benefit
    3. Solid carbohydrates may be equivalent to liquid
    4. Maintaining adequate hydration is paramount
  7. After competitive event
    1. Drink or eat 50 gram high glycemic carbohydrate ASAP
    2. Repeat high Glycemic Foods every 2 hours
    3. Take in over 100 grams carbohydrate in 4 hours
    4. Take in over 600 grams carbohydrate in 24 hours
    5. Start simple, liquid high Glycemic Food and advance

IV. Management: Vitamins and Minerals

  1. Multivitamin used by up to 80% of athletes
  2. Supplementation results in no performance improvement
  3. Supplementation may be beneficial in specific cases
    1. Iron and Calcium may be deficient in women
    2. Vitamin B12 may be deficient in strict vegetarians

V. Management: Water

  1. Precautions
    1. Overhydration (and associated Hyponatremia) is as problematic as underhydration
  2. Stay hydrated
    1. Drink 1 quart non-caffeinated fluid per 1000 calories
  3. Preload fluid 10-30 minutes before competition
    1. Drink 250 to 1000 ml of liquid
  4. During Exercise
    1. Drink 4-8 ounces (150 to 250 ml) every 15 minutes
      1. Current recommendations are to drink to thirst to avoid overhydration and Hyponatremia
      2. Some recommend limit of 800 ml per hour
    2. Drink cool water
      1. Temperature for maximal water absorption: 40 F
    3. Add 5-8% Carbohydrates if Exercise >45 minutes
      1. Carbohydrate intake totals 30 to 75 grams per hour
      2. Sports Drinks also contain electrolytes and can reduce Hyponatremia risk
        1. However, most sport drinks are hypotonic and carry Hyponatremia risk with overhydration
  5. Post event
    1. Replace each pound of weight loss with 480 ml (16 oz)
    2. Replace half fluid losses in first 4 hours
    3. Replace half fluid losses in next 8 hours

VI. Example: Foods for athletes

  1. Calcium sources
    1. Low-fat milk or yogurt
  2. Fruits and vegetables
    1. Bananas
    2. Oranges
    3. Broccoli
    4. Apricots
    5. Cantaloupe
    6. Carrots
    7. Green pepper
    8. Kiwi
    9. Strawberries
    10. Sweet potato
    11. Winter squash
  3. Carbohydrates
    1. Potatoes
    2. Whole grain breads, bagels or crackers
    3. Fortified cereal
    4. Pasta with tomato sauce
    5. Thick crust vegetarian pizza (low fat cheese)
  4. Protein sources
    1. Extra-lean roast beef
    2. Fish
      1. Tuna with no mayonnaise or low-fat mayonnaise
      2. Salmon
    3. Black Beans, Kidney beans or navy beans
    4. Lentils
    5. Tofu

VII. References

  1. Clark (1994) Physician Sportsmed 22(5):60-3
  2. Dimeff (1997) AAFP Sports Medicine, Dallas
  3. Kleiner (1997) Physician SportsMed 25(10):123-4
  4. Ahrendt (2001) Am Fam Physician 63(5):913-22 [PubMed]
  5. Lemon (1992) J Appl Physiol 73:767-75 [PubMed]
  6. Tarnopolsky (1992) J Appl Physiol 73:1986-95 [PubMed]

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