About Energy And Nutrition

How food is used as a source of energy in the body

By Philip Bailey

What is food?

Food is a mixture of chemicals. All food comes from living organisms, so chemicals present in food are similar to those needed by our bodies. Food is classified into five main groups, all of which are needed by the body.

1. Carbohydrates
2. Proteins
3. Fats
4. Minerals
5. Vitamins

Carbohydrates are the body's immediate energy source so it is important to have a large daily intake of carbohydrates. They can be found in bread, potatoes, rice, pasta and maize. Carbohydrates are large molecules, so they have to be broken down by the various enzymes (enzymes are biological catalysts) found in the stomach and small intestine. Once they have been broken down into smaller molecules they can be absorbed into the blood stream through tiny capillaries, which cover the small intestine. Once the carbohydrates are in the blood stream they can reach the body cell requiring energy, a nerve cell in the brain for example. (The brain uses one fifth of the energy in the food you have eaten).

Structure of a carbohydrates
Structure of a carbohydrates (glucose)

Proteins are mainly used for construction work in the body (they are not an energy source, but the body can produce energy from proteins as a last resort but this is extremely dangerous and can kill you), building new cells, muscle cells for example. The most important use for proteins is for construction of DNA the genetic material, which contains the instructions for every cell in the human body. Proteins are also large, complex molecules, which are broken down in the same way that carbohydrates are. Once the protein (there are many different proteins) is in the blood stream it firstly goes to the liver, which transforms the protein into the correct protein, which is most urgently needed by the body. Most protein that we eat in our food is not used at all by the body and is past straight out in the next bowel movement, this mainly applies to people in the western part of the world who eat too much protein rich food for the body to handle. Proteins are found in meat, egg, soya, pulses and beans.

Structure of a protein
Structure of a protein (cystein)

Fats are the second energy source for the body; they are most commonly stored under the skin. Fats are more correctly called lipids. The body uses lipids as an energy store as when you exercise you will soon expand the energy in the carbohydrates, so you then use the lipids as an energy source. Lipids are classed as a high-energy source as they contain more energy than the same mass of carbohydrates. If too many saturated lipids are in you diet (saturated lipids come from animal fat), they will build up in the blood vessels and put an undue strain on the heart muscle, leading to a heart attack. There are many sources of lipids, a few are; animal fat on meat, peanuts and oils.

Structure of a lipid
Structure of a lipid (triglyceride)

Minerals are only needed in small amounts by the body. They help chemical reactions in the body. An important mineral is calcium, which is used for bone construction.

Vitamins are also needed in small amounts as they also help various chemical reactions in the body. There are many sources of vitamins, which include vegetable marmite*. Vitamin D is synthesised in the body by the presence of sunlight.

*Marmite is the only food to contain a certain vitamin B5 that is needed to help brain growth.

Water is needed, but not as a food. Water is the biological solvent used for all chemical reactions in the body and for making blood plasma, which one of its functions is a coolant as burning food produces a lot of heat. Milk is the perfect food as it is a mixture of all the above food types, which is why the mother naturally supplies it for the rapidly growing baby.

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