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Nutrition & Exercise Physiology

 

Check your nutrition with this comprehensive overview of nutritional needs for exercise.

Part 1 Critical elements include: carbohydrates, proteins, fats, calcium and iron .

Part 2 Electrolyte (body salts) recovery in sport

 

Carbohydrates are one of the main sources of energy for working muscles but because we have such a limited capacity to store carbohydrate it becomes important to maintain nutritional strategies that will optimize our ability to store muscle glycogen. Endurance athletes do want to ensure that if they are expending large amounts of energy daily, that they choose carbohydrate-rich selections from within each food group. For instance both a croissant and a bagel are in the whole grains, breads and cereals group…however a croissant is a high fat (and high saturated fat) bread compared to a bagel. If you are watching your weight and/or want to refuel quickly, the carbohydrate rich bagel will benefit you more than a croissant will…. Even if your tastebuds disagree!

 

 

 

Carbohydrate Requirements (per kg body weight):

General Sports Activity (up to 60 min training per day/unlimited low intensity training

5-6 g CHO/kg

Moderately intense training (1-2 hrs of intense or longer duration medium intensity)

6-8 g CHO/kg

Endurance training (> 2hrs of intense training/day)

8-10 g CHO/kg

Extreme exercise (> 5 hrs of intense daily exercise)

10+ g CHO/kg

 

2.

Practice Protein Perfection

 

Protein is the sometimes forgotten nutrient in endurance athletes' diets. Protein is essential for building and repairing muscles, red blood cells and other tissues such as hair and skin. Proteins even play a role in immune function and hormone formation. Research now shows us that protein needs of endurance athletes may be double that of recommended nutrient intakes for the average Canadian. Choose quality protein sources such as fish, egg whites, low fat dairy products and lean cuts of poultry and red meats. Choose vegetarian sources of protein such as tofu, chickpeas, lentils, garbanzo beans in combination with different grains and cereals. And don't be afraid to add in some nuts! Nuts are nutrient dense bullets! They are rich in calories and unsaturated fats (primarily monounsaturated) and supply an important source of plant protein and dietary fiber. Packed full of vitamins and minerals, the average nut supplies us with sources of Vitamin E, folic acid, vitamin B-6, niacin, magnesium, zinc, copper, and potassium. They are also a source of phytochemicals - biologically active components of foods that may improve our health.

 

Protein requirements (per kg body weight):

General sports activity

1 gm/kg

Strength training

1.2-1.6 gm/kg

Endurance training

1.2-1.6 gm/kg

Adolescent /growing athletes

2.0 gm/kg

3.

"Meat" your Iron Needs

 

Iron is a component of hemoglobin (the carrier of oxygen in the blood) and myoglobin (carrier of oxygen in the muscles). Iron is also involved with enzymes of muscle metabolism…so a lack of iron means that not only do you not carry enough oxygen to the working muscles, your ability to use the oxygen once it gets there slows down!

Endurance athletes need more iron than any other, not only through iron lost in sweat, but also due to the destruction of red blood cells that occurs with foot strike hemolysis.

The heme form of iron, found in red meats is the most available form of iron for us. Include 3 servings or more of lean red meats each week as an easy way to help "meat" your iron needs. Most cereals and other grain products such as pasta, are fortified with iron, so look for these products and consume them instead of non fortified choices. These non-heme or plant sources of iron can be made more absorbable by combining them with a Vitamin C rich food. For example, drink a glass of orange juice in the morning along with your bowl of cereal.

 

Iron requirements per day:

General training - males and non menstruating females

7 mg /day

General training - menstruating females

12-16 mg/day

General training - growing adolescents

10-13 mg/day

Endurance training - males

7-17 mg /day

Endurance training - non menstruating females

7-17 mg/day

Endurance training - menstruating females

16-23 mg/day

4.

Catch the Calcium Craze and Bone Up on Calcium!

 

Calcium is a mineral essential not only for building and maintaining strong bones it also helps muscles contract (the heart beat…) and regulates nerve function. Calcium, like regular exercise, helps in the prevention of osteoporosis, a bone thinning disease that affects many Canadian men and women. Dairy products such as milk, yogurt, cheese are the primary sources of calcium and Vitamin D (which helps us to absorb the calcium) in the Canadian diet.

In a recent survey of Quebecers and Nova Scotians nutritional habits, calcium intake was shown to decrease with age. In fact, in Quebec 25% of women over the age of 35 consumed 400 mg/day or less of calcium. Yet the recommended nutrient intake for these women is 1000-1500 mg/day!

 

Calcium Requirements:

Teenage girls & boys

1200-1500 mg/day

Men & women after 25 yrs of age

1000 mg/day

Post-menopausal women

1500 mg/day

Men after 65 yrs of age

1500 mg/day

Amenorrheic athletes

1500 mg/day

Adapted from the Consensus Conference on Calcium Intake, 1994

 

 

Lactose intolerant?

 

According to research presented in the Journal of the American Dietetic Association, lactose maldigesters may be able to tolerate foods containing 6 grams of lactose or less per serving, such as hard cheeses and small servings (1/2 cup or less) of milk. So close the calcium gap and boost the calcium content of your meals and snacks!

 

Bone Up on Calcium:

Try yogurt with granola topping

Have a bowl of cereal with milk for breakfast a few times a week

Look for products labeled as an excellent source of calcium

That caffe latte may not be such a bad idea after all - a jolt of caffeine for an afternoon pick me up with the bonus of calcium!

Snack on small pieces of low fat cheese and crackers

5.

Fine tune your Fats

 

Fat is the greatest source of stored energy that we have! Fat is burned mostly during low-level activity (e.g. reading, sleeping) and long duration activity (e.g. long training runs or cycles). Fats also supply us with a source of essential fatty acids and fat-soluble vitamins. Choose lean cuts of meats, poultry and fish. If you eat canned fish, make sure that it is packed in water. Choose skim milk dairy products and consume small pieces of lower fat cheeses (30 grams). Use predominantly unsaturated fats such as vegetable fats (i.e. canola, safflower, sunflower and olive oils) rather than the saturated fats (butter, hydrogenated margarines) in cooking, on breads and in dressings. BUT enjoy fat in foods when you do choose the richer foods as a treat!

 

Electrolyte Replacement Supplements

Supplement Overview

  • Situations may occur in sport where focussed replacement of electrolytes is warranted:
  • Rapid rehydration following moderate-large fluid deficits incurred during exercise or other dehydrating activities (e.g. "making weight").
  • Replacement of large sodium losses during ultra-endurance activities.
  • Replacement of large electrolyte losses during exercise in certain individuals with high rates of sweat loss and/or high sweat content of electrolytes.
  • Standard sports drinks (10-25 mmol/L sodium and 3-5 mmol/l potassium) may not address the replacement of large electrolyte loses during and after exercise.
  • In the case of post-exercise rehydration, there is sound evidence that the replacement of electrolyte losses, particularly sodium, must occur before fluid balance is fully restored.
  • In the absence of sodium replacement, replacement of fluid by the dehydrated athlete will lower plasma sodium levels and osmolality, causing a decrease in thirst and increase in urine output despite a partially restored plasma volume. Although sodium can be replaced via the consumption of high-sodium foods (e.g. bread, breakfast cereal, or other processed savoury foods) or salt (sodium chloride) added to meals, it is often useful to ensure that electrolyte replacement is achieved via specialised electrolyte-replacement supplements or sports drinks with higher sodium content.
  • At present, the value of sodium/electrolyte replacement during exercise in reducing problems associated with large electrolyte losses from sweat is equivocal.
  • In particular, the use of sodium supplements to reduce the risk of hyponatraemia (low sodium concentrations) during ultra-endurance events is unclear.
  • Some experts feel that this potentially fatal problem can occur, in susceptible people, as a result of large sodium losses during prolonged exercise. Calculations from mathematical models of sweat and sodium losses show that plasma sodium concentrations
  • It is difficult to replace the sodium lost during prolonged periods of sweating especially if the athlete replaces fluid losses with low sodium drinks such as water and soft drinks, and meets fuel needs with low sodium choices such as fruit and jelly confectionery and some sports gels and bars.
  • Guidelines for sodium intake during prolonged exercise range from 0.5-0.7 g per litre of fluid (21-30 mmol/l) [American College of Sports Medicine 1996 position statement on fluid replacement in sport, regarding exercise greater than one hour] to 0.25-0.5 g per hour for people susceptible to the risk of hyponatraemia during ultra-endurance events [Doug Hiller, Medical Director, Ironman triathlon]. The typical intake of a standard sports drink (e.g. 700 ml per hour of Gatorade) would provide an hourly sodium replacement of 0.29 g.
  • Most case histories and observational studies of sporting events have found that severe cases of hyponatraemia are principally associated with "water intoxication" or over-hydration, where the athlete consumes fluid at a rate that is substantially higher than actual sweat losses.
  • This may occur in ultra-endurance events, particularly among slower competitors (low sweat loss due to low exercise intensity) and/or competitors who are overzealous regarding fluid replacement. Sodium replacement during exercise will not address the major risk factor for hyponatraemia.
  • There is some anecdotal information that whole body or ‘heat” cramps are associated with large sodium losses in susceptible athletes (prolonged or large losses of salty sweat). Further research is required to confirm these findings.
  • Oral Rehydration Solutions are recommended in the treatment or prevention of dehydration associated with diarrhoea and gastro-enteritis. The priority for athletes suffering from gastrointestinal upset is rehydration, rather than refuelling.

Supplement Profile

  • Oral Rehydration Solutions are manufactured according to World Health Organisation guidelines for the treatment and prevention of dehydration during diarrhoea and gastro-enteritis. In these situations, effective delivery of oral fluid replacement is best achieved by a solution that is low in carbohydrate (2% or 2 g/100 ml) and provides electrolytes in concentrations of 50-80 mmol/L sodium and 10-30 mmol/l potassium.
  • Oral Rehydration Solutions are available in a number of pharmaceutical brands, typically as individual sachets of powder to be mixed with 200-250 ml of water.
  • Other commercially availably electrolyte supplements include sachets of powder or tablets intended for addition to a sports drink.
  • Recently, new sports drinks have become available with a higher sodium content (~30 mmol/l).

Situations for Use in Sport

  • Rapid rehydration following moderate-large fluid deficits incurred during exercise or other dehydrating activities (e.g. "making weight").
  • Following exercise (or "weigh in") the athlete with a moderate-large fluid deficit should follow a rehydration plan tailored to meet their estimated fluid loss.
  • Typically, over the next hour(s) the athlete should consume a volume of fluid equal to 1.5 times their estimated fluid deficit.
  • When the rehydration period prior to an exercise bout is less than 60-120 min (e.g. weigh-in prior to a race or competition bout, recovery between repeated training or competition session), gastrointestinal discomfort may prevent the athlete from achieving this targeted fluid intake. In such a situation, that athlete should consume the greatest volume that can be comfortably tolerated.
  • Fluid intake should be accompanied by electrolyte replacement, particularly sodium, to optimise the retention of fluid and re-equilibration of body fluid. Sodium replacement can be achieved via the consumption of salt-containing foods eaten at recovery snacks and meals (e.g. bread, breakfast cereal, or other processed savoury foods) or by adding salt (sodium chloride) to meals and snacks. In some cases, particularly where the athlete has a restricted food intake or is limited to eating sports foods and snacks with a low sodium content, it may be valuable to consume sodium-containing fluids to provide a guaranteed sodium intake. Choices include sports drinks with higher sodium content, and Oral Rehydration Solutions or Electrolyte supplements added to traditional sports drinks or other beverages.
  • It should be noted that a higher sodium level reduces the palatability of most drinks. Many athletes may prefer to slightly dilute Oral Rehydration supplements rather than follow the manufacturer's instructions. If the palatability of the drink is reduced the athlete should be reminded to meet a fluid intake target, rather than let their fluid consumption be driven by voluntary intake and "enjoyment" of the drink. It should also be noted that the carbohydrate content of Oral Hydration Solutions is low, and will not contribute substantially to the athlete's refueling goals.
  • Replacement of large sodium losses during ultra-endurance activities. Replacement of large electrolyte losses during exercise in certain individuals with high rates of sweat loss and/or high sweat content of electrolytes.
  • Guidance for sodium supplementation during exercise should be made on an individual basis, and under the supervision of a sports physician or dietitian.
  • Sports Science and Medicine professionals should provide education that promotes individualised hydration practices before and during exercise to reduce excessive fluid intake and the risk of hyponatremia through water intoxication.
  • Sports Science and Medicine professionals should monitor the literature regarding sodium replacement during exercise to prevent the risk of hyponatraemia or salt-induced cramps in susceptible athletes and high-risk events.
  • Prevention and treatment of dehydration during diarrhoea and gastro-enteritis.
  • Guidance for use of electrolyte supplements during illness should be provided by a sports physician.

Concerns Associated with Supplement Use

  • There is no consensus regarding the value of sodium replacement during exercise.
  • In some situations, excessive salt supplementation during exercise may lead to gastrointestinal problems or cause further impairment of fluid balance.
  • Excessive fluid intake during exercise (substantially greater than sweat losses) is the major cause of serious cases of hyponatremia in susceptible people. Sodium replacement during exercise does not address this problem.
  • Increasing the sodium content of a drink generally reduces the drink palatability and may interfere with the voluntary consumption of fluid.
  • The Dietary Guidelines for Australians promote a reduction in sodium/salt intake by the community, due to the link between salt intake and hypertension in susceptible people. Electrolyte replacement during and after sport may be considered as a special situation for a special sub-group of the population, however, general guidelines for healthy eating should not be overlooked.

Last Updated 3/1/07

 

This fact sheet has been prepared by the AIS Department of Sports Nutrition as part of the AIS Sports Supplement Program. The AIS Sports Supplement Program has been designed for the specific needs of AIS athletes. It is recommended that other athletes and groups seek independent advice before using any supplement. © Australian Sports Commission 2007