By Paul Gough (BSc MINDI)
The past 25 years have witnessed considerable research interest in nutritional factors related to exercise and sports performance. Athletes with less than optimal fluid, nutrient, and energy intakes severely hamper their exercise capacity, ability to recover and responsiveness to training.
Therefore, an optimal diet is extremely important to provide nutrients in adequate amounts for tissue maintenance, repair and growth, while not overdoing it on the overall energy intake.
Dietary recommendations for physically active men and women must account for the energy requirements and and training demands of a particular activity or sport, on top of the athlete’s Basal Metabolic Rate. Today, I will detail some of the key food groups that play a part in the athlete’s diet.
1. Carbohydrates
No matter what your sport, carbohydrate is the critical fuel for optimal performance. Exercising muscles rely on carbohydrate as the main source of fuel. Therefore, excluding sufficient carbohydrates from the diet causes the athlete to train and perform in a state of glycogen depletion, which will lead to a significant decrease in exercise performance.
The total amount of carbohydrate that your body can store as glycogen in the liver and muscles is approximately 600-800g. Liver glycogen stores are used to top up the glucose levels in the blood to ensure that the brain maintains its essential glucose supply.
Stored glycogen also provides substantial energy during intense levels of aerobic exercise. An athlete’s diet should contain at least 55-60% of calories from carbohydrates – predominantly starches from fibre rich, unprocessed grains, fruits and vegetables.
Regular training and performance can rapidly deplete the small reserves stored in the body so the athlete is therefore required to ensure an adequate daily carbohydrate intake. In the event where glycogen stores are continually depleted, the body will then start to break down protein stores for glucose which will be detrimental as it will lead to a loss of lean muscle mass.
Recommended carbohydrate intakes can vary from 5-7g/kg/bw for the likes of rugby or GAA players up to 10-12g/kg/bw for ironman and marathon runners.
2. Protein
Your body not only needs protein, it also needs a sufficient quantity of each of the amino acids, which are the building blocks of proteins. There are 21 amino acids, nine of which are essential in the diet as the body is unable to manufacture them. Amino acids are required to manufacture the structural components of muscle tissue, enzymes, haemoglobin, antibodies, hormones and to transport proteins. Therefore, they are needed for strength, to build and maintain muscle, maintain immune function, to aid recovery and in younger athletes protein plays a key role in growth and development.
Protein is not an efficient source of fuel during exercise, but when too little energy is available from carbohydrate and fat, amino acids will be used as energy. One of the biggest myths is that large amounts of protein are required to build muscle. Your muscles can only use a limited amount of protein for growth, provided there is enough carbohydrate to fuel the strength training required for your muscles to grow. Any excess protein will be excreted from the body as urea in the urine.
Recommended protein intakes can vary from 1.2g/kg/bw for general athletes up to 2g/kg/bw for extreme strength training and should provide approximately 15% of daily energy intake.
3. Fat
Fat is the most concentrated form of energy, providing double the amount of calories as an equal portion of carbohydrate or protein. However, fat is not a readily available source of energy during exercise. Even when exercise is at low intensity, because of its low rate of utilisation fat can only provide approximately 50% of the energy needed, with the remainder coming from carbohydrate.
It is only in very extreme situations where a high fat diet may improve performance such as an ultra endurance event where the body’s glycogen stores will be challenged. Carrying extra body fat can have its advantages in certain sports such as open water swimming where fat can act as a buoyancy aid and provide insulation. However, in most sports excess body fat is simply additional dead weight, negatively affecting speed and agility.
Eating too little fat also carries risk as fat provides essential fat soluble vitamins and essential fatty acids. High fat meals are not recommended before training or competing as they tend to slow down stomach, emptying causing discomfort. Overall fat should provide approximately 20-25% of energy intake with majority coming from unsaturated plant sources.
4. Vitamins and minerals
Vitamins are organic compounds required in small amounts and they are vital in the diet as the body is unable to manufacture them. Most vitamins regulate processes essential for normal metabolism, growth and development.
Those vitamins involved in energy metabolism are like the spark plugs of the engine. They do not provide energy but are involved in the production of energy from fuel stores through metabolic reactions.
Deficiencies in any vitamin or mineral will impair metabolism, sports performance and, of course, overall health. Generally athletes diets have been shown to supply adequate vitamins and minerals, provided the diet is well planned and includes a wide variety of foods.
Tips for an athlete’s diet
•   Enjoy a wide variety of carbohydrate rich foods focusing on wholegrains, rice, pasta and potatoes and cereals.
•   Split carbohydrate into several meals and snacks through the day.
•   Decrease your carbohydrate intakes when training decreases or during off season as any excess will cause weight gain.
•   Limit intake of both added and hidden sources of fat such as butter, margarine, peanut butter, processed meats, chocolate, crisps and cakes.
•   Read labels to get an indication of the fat content of foods.
•   Use low fat cooking methods such as grilling, steaming or baking.
•   Choose a variety of protein rich foods.
•   Always choose lean meats and low fat dairy products.
•   Dried beans and lentils are a good method of increasing protein content of stews.
•   To increase muscle mass you need to follow your eating plan and training programme. If you only concentrate on high protein intakes without enough carbohydrate, then the protein will be used as energy instead of being used to build muscle.
•   Enjoy eating a wide variety of fruits and vegetables, the more colour and crunch the better. Aim for an intake of at least five portions per day.
•   Limit the storage and cooking times of vegetables to stop the destruction of their vitamin and mineral content.
•   Where possible choose fresh produce especially those in season. Frozen vegetables are also a good choice.
•   Most importantly eat a wide variety of different foods frequently to obtain all the nutrients required.
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Further sports nutrition articles in Paul Gough’s series for JOE will include: Pre-event nutrition and the pre-event meal, eating for recovery, hydration & supplements and sports foods.
For further information or more specific dietary information please visit www.peaknutrition.ie or contact Paul Gough at info@peaknutrition.ie.
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