Carbohydrates
There are two main types of carbohydrate:
- Complex, ‘starchy’ carbohydrates, also known as polysaccharides, found in bread, pasta, potatoes, rice and cereals.
- Simple, ‘sugary’ carbohydrates, also known as monosaccharides (e.g. glucose, fructose and galactose) and disaccharides (e.g. sucrose, lactose and maltose), found in sweets, fruit and other sugary foods.
In a balanced diet, around 50% of total energy intake (60–70% for serious sport participants) should come from the complex and simple carbohydrates, and this should be largely complex ‘starchy’ carbohydrates. You do not need to cut out sugary food completely, it’s just important to get the balance right. It is recommended that athletes consume 6-10 g of carbohydrate per kg body weight per day. This equates to 420-700g/day for a 70kg man
Protein
Most of the protein in the body is stored in tissues, particularly muscle tissue. Proteins are required for tissue growth and repair, so for serious sports participants, protein requirements are slightly higher than those of non-participants. Protein should comprise about 15% of the total energy intake for sports participants.
As a guide, current knowledge suggests that protein requirements for endurance athletes are 1.2-1.4g/kg body weight per day for endurance athletes, and 1.6-1.7g/kg body weight for strength trained athletes. These increased intakes can generally be met through diet alone, as overall food intake naturally increases as energy expenditure goes up, so by default the amount of protein consumed also increases.
Protein is found in dairy products, such as cheese and eggs, and in meat, poultry, fish and nuts. Dairy products can also contain a lot of fat, so try to choose lower fat alternatives where possible (e.g. skimmed/semi-skimmed milk and low fat yogurts).
The role of protein
As a major functional and structural component of all cells in your body, protein is the most important building material for muscles, hormones, enzymes and the immune system.
Proteins are formed from building blocks known as ‘amino acids’. All the body’s proteins are made up from various combinations of the same twenty different amino acids. Of the twenty amino acids, eight cannot be made in the body and have to be ingested with your food. These are valine, leucine, isoleucine, threonine, methionine, phenylalanine, tryptophane and lysine. These are known as the essential amino acids and you should ensure that you are consuming the recommended daily allowance of all eight of these amino acids. As a sports participant, the essential amino acids valine, leucine, and isoleucine are of particular importance as these are used when your body uses protein as an energy source
Fats, vits and minerals
Fat
Fat is also used for energy. It is a concentrated energy source and an important part of our diet as it provides fat soluble vitamins and essential fatty acids as well as energy to help fuel endurance exercise. However fat intake should be relatively low and should comprise no more that 25-30% of total energy intake - with less than 10% coming from saturated fat. Many foods contain fats, including oil, butter, dairy products, meat and nuts.
Vitamins and minerals
Vitamins and minerals are essential for converting other food sources into energy and are vital for maintaining the overall good health of the body. Vitamins and minerals can be obtained from all natural food sources, including fruit and vegetables, red meat and dairy products.
Glucose is the body’s preferred energy source during exercise and any excess glucose not immediately required by the body is stored as glycogen in the liver and muscles. However, glycogen stores have a limited capacity. An average person can store only 250–300 g of glycogen. With training and a proper diet containing lots of carbohydrate, this can be increased to about 600 g but this is still relatively little. So, glycogen stores need to be topped up regularly to ensure the body has sufficient energy readily available.
Amino acids derived from protein are used for tissue growth and repair. The body does not store amino acids as an energy reserve and they are not a major source of fuel during exercise.However if you are energy deficient, muscle tissue may be broken down to provide energy.
Fatty acids are used as the main alternative energy source to glucose, particularly during lower intensity endurance exercise, but the body cannot convert them into energy as quickly as it can carbohydrates. The body stores excess fatty acids as fat around the major abdominal organs and under the skin. These stores have an unlimited capacity and can continue storing excess fat eventually leading to clinical obesity.
Excess glucose and amino acids can also be converted to fat and stored by the body.
To use energy from food, glucose, fatty acid and, under certain cirumstances, amino acid molecules, are used to make a high-energy molecule called adenosine triphosphate (ATP). Your body then uses ATP for all its energy dependent processes
