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:
- more than 55 per cent from carbohydrates
- about 12 to 15 per cent from protein
- less than 30 per cent from fat.
Athletes who exercise strenuously for more than 60 to 90 minutes every day may need to increase the amount of energy they get from carbohydrates to between 65 and 70 per cent.
More recent advice also provides guidelines for carbohydrate and protein based on grams per kilogram (g/kg) of body weight. 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, nuts, 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 sugar (glucose), which is the body’s primary energy source. 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 is compromised because there is not enough glycogen kept in storage to fuel the body. 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): 3–5 g/kg/day
- Moderate intensity exercise (60 mins/day): 5–7 g/kg/day
- Endurance exercise (1–3 hrs/day): 6–10 g/kg/day
- Extreme endurance exercise (more than 4 hrs/day): 8–12 g/kg/day
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.
More research is required to confirm the best recommendations for sports nutrition. However, there is a suggestion that low GI foods may be useful before exercise to provide a more sustained energy release.
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.
The pre-event meal is an important part of the athlete’s pre-exercise preparation. A high-carbohydrate meal three to four hours before exercise is thought to have a positive effect on performance. A small snack one to two hours before exercise may also benefit performance.
Some people may experience a negative response to eating close to exercise. A meal high in fat or protein is likely to increase the risk of digestive discomfort. It is recommended that meals just before exercise should be high in carbohydrates and known not to 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.
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 30-60 g of carbohydrate is sufficient, and can be in the form of lollies, sports gels, 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 four 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 two hours after exercise. To top up glycogen stores after exercise, eat carbohydrates with a moderate to high GI 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, muffin/crumpets, fruit and yoghurt.
Protein and sporting performance
Protein is an important part of a training diet and plays a key role in post-exercise recovery and repair. Protein needs are generally met by following a high-carbohydrate diet, because many foods, especially cereal-based foods, are a combination of carbohydrate and protein.
The amount of protein recommended for sportingis only slightly higher than that recommended for the general public. For example:
- General public and active people – the daily recommended amount of protein is 0.8–1.0 g/kg of body weight (a 60 kg person should eat around 45–60 g of protein daily).
- Sports people involved in non-endurance events – people who exercise daily for 45–60 minutes should consume between 1.0–1.2 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 1.2–1.7 g/kg of protein of body weight per day.
Dietary surveys have found that most athletic groups comfortably reach and often exceed their protein requirements by consuming a high-energy diet. Protein supplements are therefore unlikely to improve your sporting performance.
While more research is required, other concerns associated with very high-protein diets include:
- increased cost
- a potential negative impact on kidney function
- increased weight if protein choices are also high in fat
- a lack 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. Supplements will only be of any benefit if your diet is inadequate or you have a diagnosed deficiency, such as an iron or calcium 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:
- 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.
Use of vitamin and mineral supplements is also potentially dangerous. Supplements should not be taken without the advice of a qualified health professional. It’s best if dietary imbalances are adjusted after analysing and altering your diet, instead of by using a supplement or pill.
It’s also important to remember that if you take supplements, you are at risk of committing an anti-doping rule violation no matter what level of sport you play.
Water and sporting performance
Dehydration can impair athletic performance and, in extreme cases, may lead to collapse and even death. Drinking plenty of 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.
Using salt tablets to combat muscle cramps is no longer advised. It is lack of water not sodium that affects the muscle tissue. Persistent muscle cramps might be due to zinc or magnesium deficiencies.