In first year medical school, I drew the Krebs cycle by hand. Every step. Every molecule. Every carbon atom shuffling its way through the mitochondrial matrix like it had somewhere important to be. I thought it was genuinely fascinating. I also thought I would never need to know this again the moment the practical exam was over.

I was correct for approximately thirteen years.

Then my own cells stopped making energy properly and suddenly the Krebs cycle was the most relevant thing I had ever memorized. Funny how that works.

Here is the biology class you slept through, taught by someone who drew all the molecular structures, forgot them immediately, and had to learn them again the hard way.

Your cells are running a factory you've never thought about

Every cell in your body contains hundreds to thousands of mitochondria. You probably remember them as "the powerhouse of the cell," which is the one fact that survives the great purge of high school biology knowledge. What you might not remember is what that actually means at the molecular level, because your teacher said ATP and your brain said nap time.

ATP is adenosine triphosphate. It is the actual currency your body runs on. Not calories. Not macros. Not whatever vibes your wellness app is tracking. ATP. Every single thing your body does, thinks, feels, or fights off requires it. Movement. Cognition. Immune function. Hormone production. Healing. All of it runs on ATP, produced in a three-step process that is frankly more interesting than it sounds, which I admit is a low bar.

Step one: glycolysis. Happens in the cytoplasm. Breaks glucose down into pyruvate. Nets 2 ATP. Respectable but not impressive.

Step two: the Krebs cycle. Runs in the mitochondrial matrix. The one I drew seventeen times in first semester. Extracts electrons from the pyruvate and passes them along. Nets another 2 ATP. Still not the main event.

Step three: the electron transport chain. This is where things get interesting. Running along the inner mitochondrial membrane, using the electrons from step two and the oxygen from every breath you take, this chain produces up to 34 ATP. A healthy cell at full capacity generates approximately 38 ATP from a single glucose molecule.

That is the number your entire life runs on.

What happens when the factory breaks

The electron transport chain is where most of your energy comes from. It is, not coincidentally, also where things go wrong first.

In 2023, NIH researchers published findings identifying a protein called WASF3 that physically disrupts the assembly of the respiratory complexes running this chain. They found it significantly elevated in muscle tissue samples from ME/CFS patients compared to healthy controls. When WASF3 levels were experimentally reduced, mitochondrial function improved.

This is not a fringe theory. This is the National Institutes of Health publishing in one of the most prestigious scientific journals on the planet.

Separately, research has confirmed that chronic stress causes direct oxidative damage to the mitochondrial membrane. Measurable, structural damage to the machinery itself. The HPA axis dysregulates, cortisol patterns flatten, oxidative stress accumulates, and the ATP factory takes hits from multiple directions simultaneously.

And then there is long COVID. Over 65 million people worldwide are currently living with it. Researchers have now documented that ME/CFS and long COVID share the same mitochondrial damage signature. The same disrupted respiratory complexes. The same measurable reduction in ATP output. The same exhaustion that no standard workup has been able to explain.

The explanation exists. It just requires looking past the basic things on the standard panel. Mostly because we don't have tests for the mitochondria just yet. 

The part your doctor probably missed, and honestly, why would they have looked

Mitochondrial dysfunction does not show up on a basic metabolic panel. It does not show up on a CBC. It does not show up on a TSH. The tests your doctor ordered were not designed to find this, and ordering them was not negligence. It was a system doing exactly what it was built to do, which is check the obvious things quickly and move on to the next patient.

Normal labs mean the things that were tested were normal. Full stop. They do not mean you are fine. They mean we stopped looking before we got to the interesting part.

I spent years inside that gap. The specific loneliness of being told by objective data that nothing is wrong while your body insists otherwise is something I would not wish on anyone. The data was not lying. It was just incomplete.

So what do you do with this

Fatigue is not one thing. It is not a personality trait. It is not anxiety wearing a trench coat. It is not what happens when you need to go to bed earlier or drink more water or take up yoga, and if one more person suggests yoga I am going to need a moment.

It is a signal. Signals have sources. Sometimes the source is mitochondrial. Sometimes it is hormonal, immune, neurological, or some combination of three things quietly compounding while you white-knuckle your way through another Tuesday.

The Krebs cycle I memorized in medical school and promptly forgot turned out to be one of the most clinically useful things I ever learned. It just took my own body falling apart for me to remember why.

If you want to figure out which categories are driving your fatigue, start with the Fatigue Quiz.

Because the answer exists. It has always existed. Someone just needs to go find it.

If you want to figure out which categories are driving your fatigue, start with the Fatigue Quiz. Five minutes. It covers the four most common drivers. It is not the whole picture. It is a very good place to start. Take the Fatigue Quiz.

Board certified in family medicine, professionally exhausted, aggressively solutions-oriented.