How Autophagy Works – and Why It’s Beneficial for Longevity

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by Nils Osmar. Updated Novembe 19, 2022. Medical disclaimer.

Imagine that you’re alone in the woods, and it’s freezing outside –– and the temperature is dropping steadily. You need heat to survive. You have some matches, but no fuel.

Then you notice that there actually is some fuel nearby: twigs and branches and sticks littering the forest floor. So you gather them up, put them in a pile and start a fire. 

This is similar to autophagy, a process the human body goes through when we’re fasting. We feel hungry, and we need a few grams of protein to fuel our basic life processes. We need protein — somewhere around 15 or 16 grams — to stay alive. But there’s no protein coming in. 

Then we notice that there actually is a protein source nearby: all the viruses, bacteria, protein fragments, and other debris that has accumulated in our cells waiting to be disposed of.

“Burning” cellular debris

So our body goes through our cells collecting this random junk, then puts it in a big pile and “burns” it, converting it into amino acids. It then assembles them into proteins that can keep our heart beating and other life processes operating till we start eating again.  

So far so good. Autophagy is humming along, keeping us healthy even without food. And it’s cleaning potentially harmful accumulated debris out of our cells — a win-win situation.

Running 0ut of fuel

The twigs and sticks fuel the fire and keep you warm for a while. But in a day or two, you start noticing a problem. You’ve run out of debris to burn, or or running low. You’ve burned the ones that are readily available — just as, when you’re fasting, your body will by that time have burned all the easy-to-find debris in your cells. The fire is burning low, and it’s still cold outside. 

So you decide to cut down a tree, and use the wood for fuel to keep the fire burning. You choose an old, half-dead tree to cut down, so as to do minimal damage to the forest.

This is similar to apoptosis, a phenomenon that kicks in two or three days into a fast, when the body starts killing its own cells for fuel. It does not prioritize getting rid of healthy cells. It finds broken, malfunctioning senescent cells, deactivates them and begins cannibalizing them.

The body now has fuel again, a rich supply of amino acids it can assemble into proteins — and as a bonus, has cleaned out its senescent cells, the cells that trigger autoimmune problems and illness.  

In a nutshell, autophagy “takes out the cellular trash.” During autophagy, the body starts scouring the interiors of our cells looking for items to use as fuel. The items found include things like viruses, bacteria, and various types of useless clutter which have accumulated in the cell over time — junk that is “overflowing the trash bins” of our cells.  

Burning this readily available “kindling” keeps our bodies happy for a while, but eventually the “trash” will be emptied, and we’ll have run out of available items to use.

Deep autophagy clears out senescent cells

Apoptosis (deep autophagy) occurs later in a fast, and involves the actual deaths of old, broken, poorly functioning senescent cells. Fasting for three days or more should move you deeply into apoptosis.

Killing off our old, decrepit, toxic, half-dead may sound harsh, but it’s great for the body, because senescent cells are the ones that trigger allergies, autoimmune reactions, and even conditions like multiple sclerosis.

And the cells that are “killed” weren’t really fully alive in a biological sense… they were broken, malfunctioning cells, lingering and accumulating in the body but carrying on no essential functions.

Longer fasts have greater benefits

Apoptosis doesn’t happen in a short fast, but can occur in a longer one, if you’re fasting for three days or more. People are sometimes concerned about fasting destroying muscle tissue when deprived of nutrients. Recent evidence suggests that muscle is actually the last thing to go, i.e., that the body conserves muscle tissue during fasting and prioritizes getting rid of debris such as skin tags first. We may lose a very small amount of muscle mass but it’s easily regained at the end of the fast. 

Fasting versus dieting

The question gets raised now and then of whether it’s better to fast or just diet. If our only lens is weight loss, they’re fairly similar. But viewing things in terms of autophagy clarifies that fasting has long-term health benefits that go far beyond those of cutting calories. We could spend our lives “dieting” but never go into deep autophagy, and never experience the clearance of senescent cells from our bodies.

Other roads to autophagy

There are foods and supplements which can enhance this process and deepen autophagy. One example is spermidine, found in foods such as green peas, mushrooms, natto and wheat germ. It can also be intensified by exercising (particularly if we exercise when fasting), and by drinking green tea, white tea.

I view all of these as adjunct, not primary, ways or activating autophagy. The key mechanism for cleaning “junk” out of our cells is depriving ourselves of nutrients for a time. This mechanism is “highly evolutionarily conserved”, meaning it’s been a part of the biology of virtually all complex life forms on Earth almost since life began on our planet.

Water fasting is the gold standard, but for those who have trouble fasting or should not fast for medical reasons, doing a fasting mimicking diet is an alternative. I write about FMDs, and a type of FMD that I’ve done several times, on this page.



Not medical advice

This article is not intended as, and should not be taken as, medical advice. I’m not advising that people eat any particular diet or take any particular supplements, just reporting on what I’m doing. All supplements can have side effects; I would encourage people to research both possible benefits and side effects before starting on any supplementation regimen.  See full Medical Disclaimer

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