Nutrition in Sport

An Optimal Training diet

A training diet should:

Provide adequate energy and nutrients to meet the demands of training and exercise
Include a wide variety of foods and not be too rigid or restrictive
Get the athlete "in shape" (i.e. optimal body weight and body fat levels for performance)
Promote a quick and full recovery following exercise
Provide adequate fluids to ensure maximum hydration
Consider both the short and long-term health of the individual (1).

An athlete's diet should be similar to that which is recommended to the general population in terms contribution to energy (see table 1). Athletes who exercise strenuously for more than 60 to 90 minutes daily, however, may benefit from increasing the amount of energy that they derive from carbohydrate (2).

Table 1: The percentage of macronutrient contribution to energy for athletes and the general population

Source: Burke, L. and Deakin, V. 1994 (2)

Eating strategies

Eating strategies should be tailored to maximise performance in the particular sport in which the individual is involved. The type and timing of food eaten are often specific for different sports and also for different individuals. It is, however, important to practice eating strategies during training so they can be implemented during times of competition.

Carbohydrate

Carbohydrate-rich foods, especially complex carbohydrates (those containing starch and/or fibre), should form the basis of the diet. They are important for building glycogen stores in the muscle and liver. Glycogen is the most important fuel/energy source for the body.

For optimal storage of glycogen, an athlete should aim to consume between 7-10g of carbohydrate per kilogram of body weight per day (2). This generally translates to 500 to 600 grams of carbohydrate per day (see table 2).

If carbohydrate is restricted, a poor exercise capacity will result from poor glycogen stores in the muscles and liver. A low-carbohydrate diet leads to a loss of protein tissue (and therefore muscle), as well as urinary loss of essential ions, such as potassium (1). Such eating regimes should therefore be avoided due to their detrimental impact on sporting performance.

Table 2: Carbohydrate content of some foods and beverages

Source: English, R. and Lewis, J. 1992 (3)

Eating large amounts of carbohydrate-rich foods can sometimes be difficult for an athlete. Foods containing fibre are often filling and therefore the athlete may not consume enough food to meet their energy requirements. Strategies to meet carbohydrate requirements include:

Adding more refined carbohydrate sources to "top up" intake i.e. white bread, honey, fruit juice, sports drinks and liquid meals, and lollies such as jubes and snakes.

Eating smaller, more frequent meals thereby spreading food intake over the day, rather than eating large amounts of bulky food in fewer sittings.

More recently the Glycaemic Index (GI) of food has received attention for its use in a sporting situation. The GI ranks carbohydrate-rich foods based on their rate of digestion and absorption (1). Moderate to high GI foods can efficiently deliver carbohydrate to the body during exercise and recovery. It should be remembered, however, that when dealing with whole diets, foods generally aren't eaten in isolation therefore the GI has only a limited application due to the interactions between foods.

Protein

Protein is an important part of a training diet, as plays a key role in post-exercise recovery and repair. Protein needs are generally met when following a high-carbohydrate diet, because many foods, especially cereal-based foods, are a combination of carbohydrate and protein.

Protein is derived from both plant and animal foods. Good sources of protein include:

lean beef and lamb
fish
eggs
milk
chicken
baked beans and lentils
pasta and rice
nuts (i.e. almonds)
breakfast cereals

The recommended protein requirements for different athletic types are shown in table 3.

Table 3: Protein requirements for different athletes

Source: Burke, L. 1992 (5)

Dietary surveys have found that most athletic groups comfortably reach the above targets, by consuming a high-energy diet that meets the recommended protein ratio (12-15%)(1). Nevertheless, protein and amino acids (the building blocks of protein) are popular nutritional supplements.

Amino acids are important in many metabolic pathways affecting exercise metabolism, therefore many people believe that additional protein or even specific amino acid supplements will provide additional benefits for athletes involved in intense training (5). However, dietary supplementation of protein above that necessary to maintain nitrogen balance is not likely to confer any benefit for athletes (4,6).  Undue emphasis on protein in the diet is therefore somewhat misguided and potentially dangerous to both short and long term health (1). Health complications include:

weight gain, if food choices are also high in fat
kidney failure
increased uric acid and ammonia excretion (toxic)
increased calcium loss (4)

Pre-exercise

A high-CHO meal generally 1 to 2 hours before an event, is thought to have a positive effect on exercise performance. The pre-event meal should be:

Easily digestible
High-carbohydrate
Low-fat
Low-fibre
Known not to cause gastrointestinal upset

For endurance events, a snack of around 50 grams of carbohydrate is recommended just prior to competition to top up energy supplies (see table 2).

Suitable pre-competition snacks include:

Fresh fruits and juices
Muesli bars (without chocolate coating)
Bread/toast/English muffins
Low-fat yoghurt
Cereal with low fat or skim milk
Popcorn (unbuttered)

During Exercise

When exercise lasts more than 60 minutes, it is often advantageous to consume some source of carbohydrate during exercise to top up blood glucose levels and delay fatigue (i.e 30 to 60 g of carbohydrate/kg of body weight/hour) (9).

Comfort is an important factor when consuming food or drink during exercise. Low fat and low fibre food sources are ideal in these situations i.e. sandwiches, lollies. Sports drinks and very dilute cordial or fruit juice are also useful, as they offer the benefit of delivering both carbohydrate and fluid.

Post Exercise

High carbohydrate intakes after exercise are needed to replace glycogen in the muscle and liver, and to repair any damage caused by exercise (8). In the first 24-hour period following exercise, the diet should focus on both simple and complex carbohydrates, while the second 24-hour period should focus on complex carbohydrates (1).

When a quick recovery is needed, a carbohydrate-rich meal or snack during the first two hours after exercise accelerates glycogen restoration to both the muscle and liver. It is often recommended to ingest one to two grams of carbohydrate per kilogram of body weight, preferably in small amounts every 15 to 20 minutes (9). Moderate to high GI food choices are recommended. However, the amount of carbohydrate consumed rather than the timing of ingestion is more critical.

Exercise should be avoided during the recovery period.

Fluids

Fluids should not be neglected as they are important in:

regulating body temperature
maintaining blood volume
efficiently using the body's energy stores.

High fluid intakes are needed to replace fluid loss from sweat and energy expenditure (9). The thirst mechanism should not be relied upon as an indication to drink.

As with food, drinking strategies should be devised and practised during training.   Table 4, suggests the upper limits of fluid intake relevant for athletes participating in continuous activity of a fairly high intensity. Fluid ingestion is especially important in warm and humid conditions.

Table 4: Suggested timing and amount of fluid intakes recommended before, during and after training

Source: Deakin, V. 1995 (9)

Water is the preferred fluid in most situations, however, sports drinks can be useful in ultra-endurance events (greater than 90 minutes) or when a quick recovery is necessary (2). Pregnant women, children, adolescents and the elderly should pay particular attention to their fluid intake.

Alcohol should be avoided immediately after exercise as it aggravates dehydration and interferes with glycogen resynthesis in the muscles and liver (10).

Vitamins and Minerals

A well-planned and balanced diet should meet an athlete's entire vitamin and mineral needs (9). True vitamin and mineral deficiencies are rare and supplements are seldom recommended. The indiscriminate use of vitamins and minerals supplements is potentially dangerous and should not be taken without the advice of a qualified health professional (2). Dietary imbalances should be rectified by analysing and altering the diet rather than using a supplement or pill. Furthermore, it is likely that if the intake of one vitamin or mineral isn't meeting recommended levels, then the intake of others may also be sub-optimal (2).

Iron and calcium are two minerals that are of particular concern to athletes (1). A concerted effort should be made, particularly by women, to include foods that are rich in these minerals. Where an iron deficiency has been identified through blood diagnosis, supplements may be prescribed. It should be noted, however, that iron supplements should only be taken under medical supervision due to toxicity issues (2).

Good nutrition can aid performance in sporting situations. Diets should be well planned and practiced in a training situation. Fluids should not be neglected and fad diets should not be followed due to their unknown and potentially damaging impact on athletic performance and health.

 For more information on sports nutrition, contact a sports dietitian or nutritionist.

References

1. Hawley, J. and Burke, L. 1998 Peak Performance Allen and Unwin, St Leonards, Australia.
2. Burke, L. and Deakin, V. 1994 Clinical Sports Nutrition, McGraw-Hill, Sydney.
3. English, R. and Lewis, J. 1992 Nutritional Value of Australian foods, Australian Government Publishing Service, Canberra.
4. Burke, L. 1992 Protein and amino acid needs of the athlete, State of the Art Review, No 28, National Sports Research Centre, Canberra.
5. Kreider 1999 Effects of protein and amino-acid supplementation on athletic performance, Sportscience, 3(1), sportsci.org/jour/9901/rbk.html
6. Read, R.S.D. and Kouris-Blazos, A. 1997 'Foods, physical activity and sport' In Food and Nutrition: Australasia, Asia and the Pacific Ed. Mark L. Wahlqvist, Allen and Unwin Pty Ltd, St Leonards.
7. Burke, L. 1992 The complete guide to food for sports performance: a guide to peak nutrition for your sport. North Sydney: Allen and Unwin.
8. Ivy, J.L. 1991 Muscle glycogen synthesis before and after exercise, Sports Medicine, 11, pp 6-19.
9. Deakin, V. 1995 Training Nutrition, State of the Art Review, No 37. National Sports Research Centre, Canberra.
10. O'Brien, C.P. 1993 Alcohol and sport: Impact of social drinking on recreational and competitive sports performance, Sports Medicine, 15, pp 71-77.

Useful Links

Sport Science   U.S. site for the Internet Society for Sport Science
Arbor Nutrition Guide  (Look under Clinical then Sports Nutrition)

 

Last Updated: March 28, 2001