Nutrition and exercise
The link between good health and good nutrition is well established. Interest in nutrition and its impact on sporting performance is now a science in itself.
Whether you are a competing athlete, a weekend sports player or a dedicated daily exerciser, the foundation to improved performance is a nutritionally adequate diet.
Daily training diet requirements
The basic training diet should be sufficient to:
- provide enough energy and nutrients to meet the demands of training and exercise
- enhance adaptation and recovery between training sessions
- include a wide variety of foods like wholegrain breads and cereals, vegetables (particularly leafy green varieties), fruit, lean meat and low-fat dairy products to enhance long term nutrition habits and behaviours
- enable the athlete to achieve optimal body weight and body fat levels for performance
- provide adequate fluids to ensure maximum hydration before, during and after exercise
- promote the short and long-term health of athletes.
The athlete’s diet
An athlete’s diet should be similar to that recommended for the general public, with energy intake divided into:
- 45 to 65% from carbohydrates
- 15 to 25% from protein
- 20 to 35% from fat.
Athletes who exercise strenuously for more than 60 to 90 minutes every day may need to increase the amount of energy they consume, particularly from carbohydrate sources.
Guidelines for carbohydrate and protein based on grams intake per kilogram (g/kg) of body weight are also available.
The current recommendations for fat intake are for most athletes to follow similar recommendations to those given for the general community, with the preference for fats coming from olive oils, avocado, nuts and seeds.
Athletes should also aim to minimise intake of high-fat foods such as biscuits, cakes, pastries, chips and fried foods.
Carbohydrates and exercise
During digestion, all carbohydrates are broken down into sugars (primarily glucose), which are the body’s primary energy source.
After absorption, glucose can be converted into glycogen and stored in the liver and muscle tissue. It can then be used as a key energy source during exercise to fuel exercising muscle tissue and other body systems.
Athletes can increase their stores of glycogen by regularly eating high-carbohydrate foods.
If carbohydrate in the diet is restricted, a person’s ability to exercise may be compromised because there is not enough glycogen kept in storage to fuel the body.
If dietary protein intake is insufficient, this can result in a loss of protein (muscle) tissue, because the body will start to break down muscle tissue to meet its energy needs, and may increase the risk of infections and illness.
Carbohydrates are essential for fuel and recovery
Current recommendations for carbohydrate requirements vary depending on the duration, frequency and intensity of exercise.
Foods rich in unrefined carbohydrates, like wholegrain breads and cereals, should form the basis of the athlete’s diet. More refined carbohydrate foods (such as white bread, jams and lollies) are useful to boost the total intake of carbohydrate, particularly for very active people.
Athletes are advised to adjust the amount of carbohydrate they consume for fuelling and recovery to suit their exercise level. For example:
- light intensity exercise (30 mins/day): 3 to 5 g/kg/day
- moderate intensity exercise (60 mins/day): 5 to 7 g/kg/day
- endurance exercise (1 to 3 hrs/day): 6 to 10 g/kg/day
- extreme endurance exercise (more than 4 hrs/day): 8 to 12 g/kg/day.
Training with low carbohydrate availability
There may be some situations in an athlete’s training program that warrants a period of restricted carbohydrate intake. A more recent strategy adopted by some athletes is to train with low body carbohydrate levels and intakes (train low).
There is accumulating evidence that carefully planned periods of training with low carbohydrate availability may enhance some of the adaptations in muscle to the training program. However, currently the benefits of this approach to athletic performance are unclear.
Sporting performance and glycaemic index
The glycaemic index (GI) ranks food and fluids by how ‘carbohydrate-rich’ they are and how quickly they affect the body’s blood sugar levels. The GI has become of increasing interest to athletes in the area of sports nutrition.
Evidence does not generally support a significant impact of manipulation of GI in the diet on exercise performance, assuming total carbohydrate and energy intake are sufficient in an athlete’s diet. However, the particular timing of ingestion of carbohydrate foods with different GIs around exercise might be important.
There is a suggestion that low GI foods may be useful before exercise to provide a more sustained energy release, although evidence is not convincing in terms of any resulting performance benefit.
Moderate to high GI foods and fluids may be the most beneficial during exercise and in the early recovery period. However, it is important to remember the type and timing of food eaten should be tailored to personal preferences and to maximise the performance of the particular sport in which the person is involved.
Pre-event meal
The pre-event meal is an important part of the athlete’s pre-exercise preparation.
A high-carbohydrate meal 3 to 4 hours before exercise is thought to have a positive effect on performance. A small snack one to 2 hours before exercise may also benefit performance.
It is important to ensure good hydration prior to an event. Consuming approximately 500 ml of fluid in the 2 to 4 hours prior to an event may be a good general strategy to take.
Some people may experience a negative response to eating close to exercise. A meal high in fat, protein or fibre is likely to increase the risk of digestive discomfort. It is recommended that meals just before exercise should be high in carbohydrates as they do not cause gastrointestinal upset.
Examples of appropriate pre-exercise meals and snacks include cereal and low-fat milk, toast/muffins/crumpets, fruit salad and yoghurt, pasta with tomato-based sauce, a low-fat breakfast or muesli bar, or low-fat creamed rice. Liquid meal supplements may also be appropriate, particularly for athletes who suffer from pre-event nerves.
For athletes involved in events lasting less than 60 minutes in duration, a mouth rinse with a carbohydrate beverage may be sufficient to help improve performance. Benefits of this strategy appear to relate to effects on the brain and central nervous system.
Eating during exercise
During exercise lasting more than 60 minutes, an intake of carbohydrate is required to top up blood glucose levels and delay fatigue.
Current recommendations suggest 30 to 60 g of carbohydrate is sufficient, and can be in the form of lollies, sports gels, sports drinks, low-fat muesli and sports bars or sandwiches with white bread.
It is important to start your intake early in exercise and to consume regular amounts throughout the exercise period.
It is also important to consume regular fluid during prolonged exercise to avoid dehydration. Sports drinks, diluted fruit juice and water are suitable choices. For people exercising for more than 4 hours, up to 90 grams of carbohydrate per hour is recommended.
Eating after exercise
Rapid replacement of glycogen is important following exercise.
Carbohydrate foods and fluids should be consumed after exercise, particularly in the first one to 2 hours after exercise.
While consuming sufficient total carbohydrate post-exercise is important, the type of carbohydrate source might also be important, particularly if a second training session or event will occur less than 8 hours later. In these situations, athletes should choose carbohydrate sources with a high GI (for example white bread, white rice, white potatoes) in the first half hour or so after exercise. This should be continued until the normal meal pattern resumes.
Suitable choices to start refuelling include sports drinks, juices, cereal and low-fat milk, low-fat flavoured milk, sandwiches, pasta, muffins/crumpets, fruit and yoghurt.
Since most athletes develop a fluid deficit during exercise, replenishment of fluids post-exercise is also a very important consideration for optimal recovery. It is recommended that athletes consume 1.25 to 1.5 L of (non-alcoholic) fluid for every kilogram of body weight lost during exercise.
Protein and sporting performance
Protein is an important part of a training diet and plays a key role in supporting exercise adaptations and in post-exercise recovery and repair. Protein needs are generally met (and often exceeded) by most athletes who consume sufficient energy in their diet.
The amount of protein recommended for sporting people is only slightly higher than that recommended for the general public. For example:
- General public and active people – the daily recommended amount of protein is 0.8 to 1.0 g/kg of body weight (a 60 kg person should eat around 45 to 60 g of protein daily).
- Sports people involved in non-endurance events – people who exercise daily for 45 to 60 minutes should consume between 1.0 to 1.2 g/kg of body weight per day.
- Sports people involved in endurance events and strength events – people who exercise for longer periods (more than one hour) or who are involved in strength exercise, such as weight lifting, should consume between 1.2 to 2.0 g protein/kg of body weight per day.
- Athletes trying to lose weight on a reduced energy diet – increased protein intakes up to 2.0 g/kg of body weight per day can be beneficial in reducing loss of muscle mass.
High-quality dietary proteins including lean meats, milk, and eggs, can aid in the maintenance, repair, and synthesis of proteins in muscle. For athletes interested in increasing lean mass or muscle protein synthesis, consumption of a high-quality protein source such as whey protein or milk containing around 20 to 25 g protein in close proximity to exercise (for example, within the period immediately to 2 hours after exercise) may be beneficial.
As a general approach to achieving optimal protein intakes, it is suggested to space out protein intake fairly evenly over the course of a day, for instance around 25 to 30 g protein every 3 to 5 hours, including as part of regular meals.
There is currently a lack of evidence to show that protein supplements directly improve athletic performance. Therefore, for most athletes, additional protein supplements are unlikely to improve sport performance.
While more research is required, other concerns associated with very high-protein diets include:
- increased cost
- potential negative impacts on bones and kidney function
- increased body weight if protein choices are also high in fat
- increased cancer risk (particularly with high red or processed meat intakes)
- displacement of other nutritious foods in the diet, such as bread, cereal, fruit and vegetables.
Using nutritional supplements to improve sporting performance
A well-planned diet will meet your vitamin and mineral needs. Vitamin and mineral supplements will only be of any benefit if your diet is inadequate or you have a diagnosed deficiency, such as an iron or vitamin D deficiency. There is no evidence that extra doses of vitamins improve sporting performance.
Nutritional supplements can be found in pill, tablet, capsule, powder or liquid form, and cover a broad range of products including:
- vitamins
- minerals
- herbs
- meal supplements
- sports nutrition products
- natural food supplements.
Before using supplements, you should consider what else you can do to improve your sporting performance – diet, training and lifestyle changes are all more proven and cost effective ways to improve your performance. It’s best if dietary imbalances are adjusted after analysing and altering your diet, instead of by using a supplement or pill.
Relatively few supplements that claim performance benefits are supported by sound scientific evidence. Use of supplements is also potentially dangerous. Supplements should not be taken without the advice and guidance of a medical practitioner or Accredited Sports Dietician.
The ethical use of sports supplements is a personal choice by athletes, and it remains controversial. It’s important to remember that if you take supplements, you are responsible for the ingestion of these and any subsequent health, legal or safety consequences that may occur. If taking supplements, you are also at risk of committing an anti-doping rule violation no matter what level of sport you play.
Water, alcohol and sporting performance
Dehydration can impair athletic performance and, in extreme cases, may lead to collapse and even death.
Drinking plenty of non-alcoholic fluids before, during and after exercise is very important. Don’t wait until you are thirsty. Fluid intake is particularly important for events lasting more than 60 minutes, of high intensity or in warm conditions.
Water is a suitable drink, but sports drinks may be required, especially in endurance events or warm climates. Sports drinks contain some sodium, which helps absorption. A sodium content of 30 mmol/L (millimoles per litre) appears suitable in sports nutrition.
While insufficient hydration is a problem for many athletes, excess hydration may also be potentially dangerous. In rare cases, athletes might consume excessive amounts of fluids that dilute the blood too much, causing a low blood concentration of sodium. This condition is called hyponatraemia, which can potentially lead to seizures, collapse, coma or even death if not treated appropriately.
Consuming fluids at a level of 400 to 800 ml per hour of exercise might be a suitable starting point to avoid dehydration and hyponatraemia, although intake should ideally be customised to individual athletes, considering variable factors such as climate, sweat rates and tolerance.
While alcohol can be a part of a well-organized diet and in social occasions, excessive consumption can interfere with athletic performance and in the recovery from exercise. It is also energy dense and nutrient poor and can have adverse effects on health. Athletes should therefore consider the current Alcohol Guidelines and minimise or avoid consumption, particularly during the post-exercise period when optimal recovery and repair are very important.
Where to get help
- Your GP (doctor)
- Dietitians Australia Tel. 1800 812 942
- Sports Dietitians Australia Tel. (03) 9699 8634
