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 is food necessary? and why do we feel hunger?
We feel hunger because it is a body’s call to replenish or restore the reserved 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 body’s next requirement.
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.
The blood carries this glucose to provide instant energy to the body.
But if 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 into 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 between glucose and ATP formation, 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 using 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 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 the lungs, and water is excreted by the urine.
On the contrary, the plants breath in CO2 from 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. The action of the insulin hormone facilitates this.
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 Insulin’s support.
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 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 starvation, fatty acids stored convert to acetyl-CoA to produce energy through gluconeogenesis.
Similarly, amino acids also break down to produce acetyl-CoA to produce energy.
Hence a starving person looks lean and loses weight as the reserve substances are consumed to produce energy.