How do we mechanically burn calories into body heat.
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The process to create energy is cells taking the calories and oxygen then when the body breaks those bonds and creates new ones it creates more bonds then it breaks which releases energy from the energy stored in those bonds some is lost as heat and other is used for the function of those cells
We don’t actually burn them. Essentially, all of your cells need nutrients to survive, and they need to convert the chemical energy in food into energy they can use for their specific purposes.
So broadly speaking, you ingest food, the acids in your stomach break the food down, the cells in your small intestine absorb nutrients and water from the food, and your blood carries those nutrients around to all of your cells.
Inside each cell there’s a process that happens called cellular metabolism, which is a pretty complex series of chemical reactions. Those chemical reactions produce energy for each of your cells to use.
Simply put, no process is 100% lossless (except for a few oddities like superconductors that are neat science but often have little practical use). Chemical processes, muscle contractions, etc. all lose some of the energy put in as a result of this fact. In engineering, we usually want to avoid this, but in biology, it can be very useful. This is also why you shiver when you’re cold. And well, that takes energy, which we measure in calories.
Your body has a bunch of enzymes that break down molecules like glucose in a series of controlled steps. The process involves using up oxygen, and the end products are water and carbon dioxide, so it is technically burning.
In some of the steps, enough energy is released that some of it can be stored in a molecule called ATP, which is what your body uses as a battery to power its other processes. The rest of the energy is lost as heat, same as in any other process.
You can look up glycolysis if you want to see all the steps.
In one sentence – Mitochondria take the chemical energy from nutrients and convert it into an electrical voltage, which they then convert into ATP and heat.
Nutrients enter the Krebs cycle. This produces NADH and FADH, which are high-energy electron donors. Those high energy electrons get passed along the electron transport chain in the mitochondria and eventually end up given to oxygen, where they have less energy.
The energy ‘lost’ is used to power pumps that push H+ ions out of the mitochondria. This creates a electro-chemical gradient of H+ ions (more outside than inside the mitochondria) and because they’re ions, they’re electrically charged – so it’s a *voltage;* electrical potential difference. They want to diffuse back into the mitochondria, so they do, along an enzyme called ATP Synthase.
The electrical potential energy is converted back into chemical energy in the form of ATP, and a little bit is ‘lost’ as heat, because the enzyme is not 100% efficient.
The mitochondria can also intentionally increase heat production by ‘uncoupling’. It gets a new protein called Uncoupling Protein to make a hole in the membrane for the H+ ions to flow through. This means that instead of ‘some energy goes to ATP, some is heat’ *all* of the energy from the H+ ions moving turns into heat, but you can’t make ATP.
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