Carbohydrates (CHO) are a group of substances found in both plant and animals, composed of carbon, hydrogen and oxygen in the ration of 1:2:1. Foods providing carbohydrates are the cheapest sources of energy in the world. The foods rich in carbohydrates are bread, cereals, rice and potatoes, which is why we should be consuming these as part of our everyday diet. Other foods containing carbohydrates include beans, pulses, fruits, some vegetables, milk and dairy products.
In modern times carbohydrates tended to be dismissed as of little importance in the diet. For athletes this could not be further from the truth since the 1980’s the importance of carbohydrates in our diet has been recognised by nutritionists. Carbohydrates (CHO) is now put forward in preference to fat as a major source of energy and nutrients in our diet.
Carbohydrates (CHO) can be split into two categories – sugars and starches. Sugars are made up of small molecules consisting of one or two sugar units, whereas starches are made up of hundreds of sugar units joined together.
Regular exercisers and athletes should aim to achieve an intake of carbohydrates between 60-70% of the total energy intake. Alternatively, requirements can be calculated based on body weight and activity levels. Depending on activity levels requirements range from 5-10g per Kg of body mass of carbohydrates per day. The daily intake recommended for a footballer to maintain muscle mass during several days of intensive training is 500-600g or 8 -10g per Kg of body mass.
The simplest forms of carbohydrates are the sugars, which can be either single units known as monosaccharides or double units known as disaccharides. The next group is oligosaccharides that consist of chains of 3 to 10 units. Finally, there are polysaccharides, which are longer and more complex chains of sugars.
Carbohydrates are an essential nutrient which has important roles to play in the body. These include:
Acting as a major source of energy for the body and brain.
Forming structural elements of some cell membranes and cell walls.
Carbohydrates are a major source of fuel for the body. However, they are a fairly limited fuel source and constitute only 1-2% or roughly 2,000Kcal of the body’s overall energy stores. The major storage sites for carbohydrates are the liver and the muscles, and it is stored within these as glycogen. The remaining carbohydrates are found in the form of plasma glucose.
The other source is exogenous carbohydrates, which is consumed in the form of monosaccharides, disaccharides, and polysaccharides. Once consumed these carbohydrates are broken down and absorbed in the small intestine. From here they travel to the hepatic portal vein and into the liver.
Unlike fat, the body can store only a relatively small amount of glycogen. The total store of glycogen in an average body (weighing 80Kg) amounts to about 500g; approximately 400g in the muscle and 100g in the liver. This equates to about 1,600 to 2,000Kcal of stored energy (as each gram of glucose provides 4Kcals). This is enough to power just 2 hours of high intensity exercise. For this reason maintaining a carbohydrates rich diet is essential for athletes as glycogen stores can quickly become depleted. The upper limit for glycogen stores is around 15g per Kg of body mass and so the capacity for an 80Kg individual could be as much as 1200g. Therefore getting the dietary intake of carbohydrates correct is very important to optimise glycogen stores, especially for athletes and exercisers. The more glycogen that is available the longer exercise can continue before fatigue sets in.
There are both catabolic and anabolic pathways involved in the metabolism of carbohydrates. A catabolic pathway breaks down a complex material into simple molecules with the release of energy. An anabolic pathway builds simple molecules into complex materials of living tissue. Catabolism is therefore the opposite of anabolism.