The human body is a super-efficient machine, and like all machines, it needs fuel to function. To perform daily functions like breathing, walking, talking, sleeping, and working out, your body takes up energy from its fuel sources. Even when one is asleep, the body works to repair itself, the lungs still process air, the heart still supplies blood – the human body is indeed a miraculous machine that literally never rests until it rests six feet under the ground! So, it is indeed interesting to understand what is the amazing fuel that powers this wonder machine.
The food one eats, is a potential energy source. Once consumed, the body works on breaking down this food (carbohydrates, fat, and protein) and leads it through several different metabolic pathways. The by-products of these metabolic processes that break down food are:
- Carbon dioxide
- Adenosine triphosphate, a.k.a ATP
We all know what the first two are and what they do, but let’s take a look at ATP and how this becomes the most important by-product of metabolism.
What is ATP?
If you think of your body as a reserve bank, then ATP is its operational currency. All the energy we need in order to function throughout the twenty-four hours in a day (whether simple or complex tasks) is supplied by ATP molecules. ATP is also the only molecule that fuels muscle fibers with enough energy to be able to put up with muscle contractions.
Now, what are the sources of this ATP, and how does the body respond to each of these food sources? This becomes an important question if you want to understand how different macroelements are processed in the body vis-a-vis their use for energy production. So here’s how the body treats Carbohydrates, Fat, and Protein as energy sources:
Carbohydrates – the ’24-hour ATM’
Carbohydrates are very friendly, simple sugars that are broken down into glucose (the body’s choicest fuel) almost instantly – which is why a sports drink or chocolate bar can make you feel recharged as soon as you consume them. This energy can also be used for safe keeping (storage) – glucose is the body’s main energy source, and it can also be stored in the liver and muscles as glycogen. When you exercise, muscle glycogen gets converted back into a form of glucose that can only supply energy to the muscle fibers. The liver, too, converts glycogen back into glucose and releases it into the bloodstream to maintain blood sugar levels. This makes carbohydrates the most readily available and the go-to source of ATP production in the body.
Fat stores – your ‘Fixed Deposits’
Fat is the richest energy source in the body as it provides 9 calories per gram of energy, compared to 4 calories per gram coming from every gram of carbohydrate and protein. During workouts, stored fat in the body’s fat tissues (adipose tissue) is broken down into fatty acids which are released into the blood and subsequently taken up by the muscles for energy production. This doesn’t happen as instantly as carbohydrate metabolism though.
Protein – the ‘Compound Interest’
The human body does not essentially store protein like it does for fat and carbohydrate. Protein is broken down into amino acids that serve the purpose of building, maintaining, and repairing the body’s tissues, and support some physiological processes.
So there it is, folks. All the important sources of fuel for our complex vehicle. There is no best or worst source of fuel. Each of the sources have their own place in our journey.
Author credits – Nida Aziz