How do we get energy from food? How do our body burn the food to get energy? Information on carbonhydrates and fats.
Every activity of your body is carried on by its cells. Since your cells are alive and doing things, they must be using energy. Food provides the energy needed by all the living cells in your body. All of this food comes directly or indirectly from green plants. However, the sun is the real source of the energy in food. Green plants absorb radiant energy from the sun and change it into chemical energy, which is stored in the food that they make. You know that chemical energy is a form of potential energy. Before chemical energy makes things happen or does work, it must be set free by a chemical change.
One way to release chemical energy is by oxidation. During this chemical change, one or more elements oxidize, or combine with oxygen, to form compounds called oxides. At the same time, chemical energy is released and changed into heat or sometimes other forms of energy. For example, fuels such as coal and oil have chemical energy stored in them. By burning, or oxidizing, some kind of fuel, a stove gets energy to warm a room, while a locomotive gets energy to pull a train.
The food that you eat is fuel for your body, which gets oxygen from the air you breathe into your lungs. Both food and oxygen are carried by the blood to every living cell in your body. When food is oxidized in your cells, chemical potential energy is released and changed into kinetic energy that your body needs. Probably all the cells give out heat energy that keeps your body warm. Muscle-cells use energy to make your body move. Both heat and muscular energy are forms of kinetic energy.
Your body gets energy from food in somewhat the same way that a stove or a locomotive gets energy from fuel. However, there is not a little fire burning in each cell of your body. Burning is rapid oxidation with high temperature and flame.
It takes place in the firebox of a stove or a locomotive. Except in the muscle cells, oxidation of food in the body takes place slowly, somewhat like the rusting of iron. Some people think that all the food they eat is oxidized in the stomach, the lungs, or even the heart. You know why this idea is not correct. Of course, the cells in these organs are oxidizing the food that they need. But every living cell in the body must have energy. So all the cells oxidize food to get energy from it.
Carbohydrates and fats produce large amounts of energy when they are used as fuels by the cells. So these fuel foods are often called energy foods. Proteins will also supply energy, but their main use is to provide the body with building materials. Fats and carbohydrates are made of just three elements—carbon (C), hydrogen (H), and oxygen (O). Proteins contain the same elements together with nitrogen (N). When any of these kinds of food is used to produce energy, the carbon and hydrogen each combine with oxygen.
Each living cell uses food and oxygen to get the energy needed to carry on its activities. Then the cell gets rid of the used materials and takes in more food and oxygen from the blood. Most of the oxidized food has no further use in the cell. So the cell gives it out into the blood. Oxidized carbon is a gas, carbon dioxide (C02). This gets out of the blood through the lungs and is breathed out into the air. Oxidized hydrogen is water (H20). So the water formed by the oxidation of food is just added to all the other water in the body.
You can now understand how breathing helps your body use food. From the air you breathe in, your body gets oxygen to combine with food in the cells and release the energy that they need. In the air you breathe out, your body gets rid of carbon dioxide formed in the cells when food is oxidized. Perhaps you have heard breathing called respiration. Scientists use this word to mean the chemical change in which cells get energy from food by using oxygen and giving out carbon dioxide.