This article is intended solely for informational purposes. It is not meant to be taken as, and should not be construed, as medical advice. Any changes to your lifestyle or diet should be done in consultation with your doctor or health care professional.

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 — about 15 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 and assorted other debris that have accumulated in our cells, waiting to be disposed of.

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 clogging accumulated debris out of our cells — a win-win situation.

But in a day or two, you start noticing a problem. You’ve run out of twigs and sticks, or run low on them. (You’ve burned the ones that are readily available.) (And your body has 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. But not healthy cells. It finds broken, malfunctioning senescent cells, deactivates them and begins cannibalizing them.

The body now has fuel again, 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.

Apoptosis 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.

This 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.

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.