Food is a vital necessity for all humans and animals to live in.
It is also true that all of us strive every day to achieve our food.
But why food is necessary? and why do we feel hunger?
We feel hunger because it is a body’s call to replenish or restore the reserve food. The food inside the body is used for the supply of energy. So what we ate previously gives us energy now and what we eat now gives us energy in the next requirement of the body.
But the body has a very alert mechanism to use the food resources very scarcely. This helps us survive in times of lack of food.
When we eat food, it releases into the blood the reserve supply of glucose from the liver. This glucose is carried by the blood to provide instant energy to the body. But in case we don’t have food, it releases very scarcely and hence we feel weak and lethargic.
How we get Energy from Food
It is well described in biochemistry, In short, we can say that food is broken down to basic units like glucose. This glucose is converted to energy in the cell mitochondria.
1. Food breaks down to glucose, amino acids, and fats in the digestive system.
2. The Glucose molecules reach the cells and tissues by the blood. In the cells, food breaks down to produce ATP.
This ATP (Adenosine triphosphate) is the end energy molecule.
There are many intermediary steps in between glucose and ATP formation and they are outlined at the bottom.
We will concentrate on the basics of how this energy is formed here.
Glucose is a carbohydrate (CH2O), which means it has carbon (C), hydrogen (H) and Oxygen (O) in the structure. This structure is formed in the plants by the process called photosynthesis.
This photosynthesis is a process happening in the green leaves under the influence of sunlight. The light energy from sunlight is captured to form carbohydrates by the use of carbon dioxide (CO2) and water (H2O).
So, in other words, we can say that the energy (photons) from the sun is captured in carbohydrate form. When we eat these carbohydrates in the form of sugar, starch (potato) etc, this energy is released into the body cells.
During this conversion, the carbohydrate molecules are broken down back into carbon dioxide (CO2) and water (H2O).
So we breathe out the above-released CO2 by lungs and water is excreted by the urine.
On the contrary, the plants breath in CO2 by leaves and absorb water by roots to form these carbohydrates.
Thus energy from sunlight is taken by plants and given to us. In this process, CO2 and H2O are involved as principal intermediates.
How food is converted to energy the procedure in detail
a) The food we eat consists of carbohydrates, proteins, fats, etc. This gets digested in the gut to glucose, amino acids, and fatty acids respectively.
b) Glucose is stored in the liver as glycogen. Even, the amino acids that help in building protein and fatty acids are also stored. This is facilitated by the action of the insulin hormone.
c) In case of need, glycogen in the liver breaks down to glucose and is released into the blood. This is facilitated by the hormone glucagon released from the pancreas.
d) This glucose in the blood is absorbed into every tissue and the cells with the support of Insulin.
e) Inside the cell, glucose breaks down into two molecules of acetyl-CoA.
f) These Acetyl-CoA molecules enter into mitochondria and undergo a process called KREB’s cycle.
g) There each acetyl-CoA produces 2 more molecules of ATP by breaking down to the water (H2O) & carbon dioxide (CO2).
h) Overall each glucose molecule produces 32 ATP in our body.
h) This ATP acts as energy and fuels all the body movements, processes and also biochemical reactions.
Thus food is converted to energy in our body by the breakdown of glucose from it. This happens in the presence of oxygen inside the mitochondria. So mitochondria are called powerhouses of our body cells.
The oxygen required for the production of energy is captured from the lungs by the blood. Oxygen is needed on an immediate basis and continuously while glucose is produced even from the reserve supply.
Also See: How Energy is used in the body.
Interestingly, in the case of starvation, fatty acids stored convert to acetyl-CoA to produce energy by a process called gluconeogenesis.
Similarly, amino acids also breakdown to produce acetyl-CoA to produce energy.
Hence a starving person looks lean and loses his weight as the reserve substances are consumed out to produce energy.