When we eat, we eat for three reasons. The first reason is that we eat to stay alive. Without food our bodies would cease to function. The next two are to build and repair each part of the body as well as consuming different types of foods to get each part of the body to function efficiently.
The energy that is used for intense physical effort will come from carbohydrates. Carbohydrates are stored on the body in the liver and in the muscles. They come into your body through natural sugars such as fruits and juices, refined sugars like honey and soft drinks and finally as starches such as potatoes pasta and bread.
The next major source of energy for the body during exercise is the fat that is around the outside of the body. Fat, per gram, supplies a ton more energy for you than a carbohydrate does. One crazy fact about this is that according to scientific studies the amount of energy that a lean active cyclist at 150 pounds has in him is equivalent to if the cyclist weighed 275 pounds but only had carbohydrates in them. For the common person there is so much energy from fat in them each day that they need not worry at all about stocking up on fat before a race or ride. Besides any leftover protein or carbs converts to fat.
The proteins your body needs play a different but still vital role in cycling. Proteins bother build up and repair the body. They can be found in fish, meat, eggs, dairy products as well as in some vegetable products. In situations where there is extreme demands on the body, the protein in a body can also be burned to produce energy.