Diet in sport and exercise
Diet and athletic performance have always been linked. You only need to scan sports magazines to see articles and advertisements recommending various foodstuffs guaranteed to help you achieve your sporting ambitions. The promises are unlimited, so it is not surprising if you end up feeling confused about what to eat and when.
It is important to enjoy your food, and healthy eating may not mean changing your eating habits dramatically. However, it may mean substituting or trying out different types of food. When you’re taking regular exercise or are in training, you should eat normally but add extra calories to replace the energy you’re using, unless you are trying to lose weight.
You need to make sure you have sufficient carbohydrates, proteins and fats. You’ll get most (and probably all) of the vitamins and minerals you need from your food, although many people take supplements. This does no harm except in relation to vitamin A where excess intake can be toxic.
How many meals?
Your aim is to eat enough to sustain or even slightly exceed your output of energy. Many experts now feel that having frequent small meals improves your athletic performance but this can sometimes be difficult in practice. We suggest therefore that you eat at least three good meals a day, breakfast being particularly important. Although eating more of any kind of food will provide the extra fuel you need to compensate for the extra energy you’re expending, increasing your carbohydrate intake is the ideal approach.
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Proteins three main foods
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Carbohydrates three main foods
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Fats three main foods
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Minerals
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Vitamins
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Water
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The three main foods
Food is used as fuel to supply energy and as building material for the repair and growth of tissues. We need minerals, vitamins and water in addition to proteins, carbohydrates and fats.
All foods contain one or more of these six essentials. The body-building foods are proteins, water and minerals. The energy-producers are carbohydrates and fats. Vitamins and minerals help to make these processes of building body and energy production happen efficiently.
Some athletes, especially those living on their own, do not follow a well-balanced diet so, if you notice that your performance is dropping off, take a look at your eating habits.
Carbohydrates
Carbohydrates are your main source of energy. When they are combined with oxygen (oxidised) in cells, carbon dioxide and water are formed and energy is released:
Glucose + Oxygen = Energy + Carbon dioxide + Water.
Carbohydrates are classified by nutritionists as sugars, starches and fibre.
• Sugars:
Sugars are important sources of dietary energy. Glucose is used as fuel by your body’s cells, and your brain is almost entirely dependent on it for all its functions, including thinking and growth.
Excess sugars are stored in your liver as glycogen. These stores are mobilised if you’re not getting enough energy from your diet or if energy is needed quickly for exercise. If these stores are full, sugars are converted into fat and stored in adipose tissue.
• Starches:
Starchy foods are an important part of your diet. In some parts of the world, starch provides up to 80 per cent of the total energy intake. In the UK, starch provides about 24 per cent of the total energy intake.
Raw starch is very difficult to digest. Processing, such as cooking, can change the patterns of starch molecules, making it more digestible. Heating starch in water causes it to swell and thicken. This allows it to be broken down by the digestive enzyme amylase into glucose, which can be absorbed into your body.
In the UK, the major sources of starches in the diet are staple foods such as potatoes, cereal grains (wheat, barley, maize, oats and rye) and rice.
• Fibre:
Fibre is the major component of plant cell walls and is resistant to enzymes that digest food. Most of the fibre in the diet comes from fruit, vegetables and cereals. In wheat, maize and rice, the fibre is mainly insoluble, whereas in oats, barley and rye it is mainly soluble. In fruit and vegetables, the ratio of insoluble to soluble fibre is variable. Each kind of fibre plays a different role in digestion.
Soluble and Insoluble Fibre Sources
Soluble fibre
Beans, for example, baked beans
Lentils
Peas
Oats
Oranges
Apples
Insoluble fibre
Wholemeal bread
Wholemeal breakfast cereals
Wholemeal biscuits and crisp breads
Brown rice
Wheat bran
Oats
Insoluble fibre increases the bulk and wetness of faeces. It therefore prevents and relieves constipation by holding water in your bowel. The increased bulk speeds up the transit time of faeces and reduces the pressure in your bowel.
Soluble fibre has little effect on stool bulk. However, it binds bile acids, which are rich in cholesterol. The cholesterol found in bile is usually reabsorbed into your body. Soluble fibre prevents this re-absorption so more cholesterol is lost in the faeces and less is taken back into your bloodstream. This can be important in the prevention of coronary heart disease.
The digestion and absorption of carbohydrates are slower if there is a good supply of fibre in your diet. This results in a more gradual release of glucose into your blood, which is especially important for people with diabetes. Fibre makes you feel full because once it has absorbed water it has a larger bulk.
Proteins
Proteins are used mainly for building new tissue. This might make you think that increasing the amount of protein in your diet would increase your muscle size. However, extra protein in the diet is usually unnecessary because, if it exceeds 15 to 20 per cent of your dietary intake, you simply excrete it. You should aim to take protein in the form of lean meat, fish and other protein alternatives and to eat two portions of fish per week – especially oily fish, such as sardines and mackerel.
Fats
These are the energy storehouse of the body. The average 70-kilogram (kg) person has 10.5 kg of fat (15 per cent of body weight). However, in a highly trained athlete only around 5 to 10 per cent of the body weight will be fat. About one-fifth of dietary intake should be fat, with more coming from vegetable rather than animal sources.
Low-fat milk and other dairy foods are a good source of calcium but you should avoid eating foods that contain excessive amounts of fat or refined sugar.
Vitamins
Athletes are sometimes said to need more vitamins than other people, but there is no conclusive evidence that this is the case. Vitamins are essential for normal health, but they cannot be used as fuel. They are present in small quantities in most foods.
People who have a healthy diet are unlikely to require vitamin supplements.
• Vitamin B15:
Vitamin B15 or pangamic acid is known as one of the ‘super-vitamins’, and some athletes believe it to be the missing ingredient in their performance. It is dangerous. Toxic reactions to it have occurred, and one of its chemical constituents combines with saliva to form a carcinogen – a chemical that can lead to cancer formation. It is to be avoided at all costs.
Vitamin food sources
Vitamin A Carrots, green vegetables
Vitamin B complex Yeast, cereals, vegetables, fruit, milk, meats
Vitamin C Citrus fruits, blackcurrants, green peppers, potatoes
Vitamin D Cod liver oil, halibut oil
Vitamin E Vegetable oil
Vitamin K Green vegetables, liver
Minerals
Lack of minerals can produce a range of symptoms from nausea and vomiting to extreme muscular weakness.
• Sodium:
Sodium is obtained from animal foods and cooking salt. It becomes depleted during heavy sweating or in a humid atmosphere, and losing too much causes fatigue and muscular cramps. Tennis players are especially at risk and you will have seen the professionals take salt tablets between games. However, unless you sweat profusely over a very long period (more than an hour), usually in a hot environment, depletion is unlikely.
• Calcium:
This is the most common mineral in the body and an important constituent of bones and teeth. Apart from this, it also has a vital role in the clotting of the blood and in controlling the action of the heart and the muscles. It is found in milk, cheese and hard water and, if you have a healthy diet and regular exercise, you shouldn’t experience a deficiency, which leads to rickets in children and thinning of the bones (osteoporosis) in adults.
• Iron:
This is derived from eggs, meat, green vegetables and fish. Liver also has a very high iron content. It is important in the oxygen-carrying capacity of the blood and deficiency of iron leads to anaemia. This, in turn, leads to fatigue and poor physical performance. Women especially need to watch their iron intake because they lose iron through menstruation each month. They need 12 to 15 grams daily, which they may not get from an adequate diet. Many women athletes are training with anaemia. A simple blood test can check this out and, if iron supplementation fails to correct anaemia, further investigations are necessary.
Water
Around 70 per cent of our body weight is made up of water. In endurance events, such as cycling, marathons or tennis, fluid loss can be very significant, and as much as eight per cent of body weight may be lost as sweat. Dehydration is poorly tolerated by the body: it overheats, the heart rate climbs and heat exhaustion results.
When fluid is lost as sweat, more pure water than minerals is lost, and so it is more important to replace the water than the minerals. Mineral loss occurs only in extreme cases. The temperature and quantity of the water can affect how quickly it is absorbed into the body – 150 to 180 millilitres of cold water taken three to four times every hour is more cooling than warm water because it is more easily absorbed. Large volumes of water can cause bloating and breathing discomfort. Contrary to popular myth there is no evidence that cold water causes stomach cramps – although large volumes of it may.
There is no evidence that water on its own is more easily absorbed than a mixture, for example, a cordial, but isotonic fluids which have the same tenacity as body fluids are far more easily absorbed into the digestive system and therefore are more efficient in replacing fluid loss during long periods of exercise than water alone.
Training diets
Losing weight
Weight restriction is an integral part of certain sports, such as horse racing and boxing. Many athletes fast or dehydrate their bodies just to make the required weight. They use diuretics to increase their water loss through the urine, but dehydration leads to poor muscle strength and increased heart rate for the same amount of work – the opposite of what training is all about. If the athlete is still growing, this kind of restriction can lead to growth stunting.
If your sport requires you to be at a particular weight, you need to determine this early in the season, then work towards it gradually over four weeks or more, by controlling what you eat and increasing the amount of training you do.
Gaining weight
The aim here is to increase weight by increasing muscle mass. You can do this by eating more – add two or three high-carbohydrate, low-fat snacks per day. Muscle can be laid down by weight training.
The traditional body builders’ diet of egg whites and chicken (that is, high protein) is a fallacy. The most efficient way to increase muscle is to train more and the body needs carbohydrate to do this. Although you need to increase your protein intake slightly, this increase should not exceed one gram per kilogram of body weight per day.
Carbohydrate or glycogen loading
This is a dietary technique to help endurance athletes build up muscle energy stores. Although it does improve performance, it may be dangerous for older athletes (see below).
First, existing muscle stores should be depleted by taking moderately heavy exercise while not eating enough carbohydrate foods to replace what is used. This should last for two or three days; then for two or three days before the race the athlete switches to a low-exercise regime and a diet with a high carbohydrate content. The theory is that the depleted cells then super-compensate and store even greater amounts of glycogen. Less water is required during the race, but the high carbohydrate diet and the water retention that occurs may be dangerous for middle-aged and older people. Eating huge meals can also cause heart problems in susceptible individuals. Finally, this method is probably only effective in people who exercise at 80 per cent of their maximum – most people who run popular marathons do not approach this, and so they should simply stick to their normal diets with moderate increases in carbohydrate.
SIMPLE DIETARY GUIDELINES
• Try out lots of different foods and introduce changes that fit in with your lifestyle
• Try out new recipes
• Eat foods rich in carbohydrate and fibre, but bear in mind that you may have to pay a price for a high-fibre diet: more frequent visits to the toilet and sometimes the excessive passage of wind which may be socially unacceptable, so go steadily
• Whatever changes you’re making to your diet, try to make sure you still enjoy your food, and make simple changes in your eating habits that fit in with the limits of your budget and your lifestyle
• Avoid eating too many fatty and sugary foods
• Ensure that your diet provides adequate amounts of vitamins and minerals
• Don’t drink too much alcohol (28 units per week for a man and 21 units per week for a woman; one unit is equivalent to half a pint of beer, a measure of spirits or a small glass of wine)
Maintaining energy and hydration
During an event, for example, cycling or running, it is necessary to maintain energy and hydration. You shouldn’t eat during the final two hours before the event and your last meal should have a high carbohydrate content. If the event is a long one, you can continue taking fluids right up to the start and you should then have 250 millilitres every 20 minutes during the event.
