Fasting Wasn't Invented for Weight Loss

Somewhere along the way, two people could say "I'm fasting" and mean completely different things.

One might be fasting to pray.

Another might mean her eating window closed at 7 p.m.

Same word.

Very different reasons.

As a Christian, fasting doesn't feel particularly new to me. It's all through the Bible. David fasted. Esther called for a three-day fast without food or drink. Jesus fasted for 40 days in the wilderness. Daniel's experiences inspired what many Christians now call the Daniel Fast, which involves restricting certain foods rather than completely abstaining from eating.

Christians still fast in different ways today. Some abstain from food while drinking water. Some fast for part of a day. Some follow a Daniel-style fast. Some Christian traditions observe fasting or abstinence during Lent.

But the underlying idea isn't let me see if I can lose five pounds.

You're setting something aside for a reason.

And Christianity is hardly alone in this.

Muslims fast from dawn to sunset during Ramadan. Judaism includes fast days such as Yom Kippur. Fasting also appears in Hindu, Buddhist and other religious and spiritual traditions, with different rules and meanings.

Humans have been deliberately stepping away from food for a very long time.

What changed wasn't fasting. It was the question we started asking about it.

Instead of only asking why are you fasting?, we started asking:

What happens to your body when you do?

And that's where things get really interesting.

Modern intermittent fasting can sound almost mathematical.

16:8.

Fast for 16 hours. Eat within eight.

There's 14:10. Alternate-day fasting. The 5:2 approach. Time-restricted eating.

The practice that once revolved around prayer, religious observance or communal tradition became something you could track on your phone.

And researchers became interested too.

Studies have looked at whether restricting when we eat might affect weight, blood sugar and other aspects of metabolic health. Some trials have found modest benefits, although results vary and researchers are still studying the longer-term effects.

Then one scientific word made fasting considerably more fascinating.

Autophagy.

Autophagy literally means "self-eating," which sounds far more alarming than it is.

Think of it more like cellular recycling.

Cells have ways of breaking down damaged proteins and worn-out components and reusing some of that material. Autophagy is part of the body's normal cellular maintenance system.

Scientists had observed the process decades ago, but they didn't fully understand how it worked.

Then Japanese scientist Yoshinori Ohsumi started experimenting with yeast.

And this is where the story takes a turn I love.

He starved the yeast cells.

That helped him observe autophagy and eventually identify genes essential to the process.

His discoveries were so important that in 2016 he received the Nobel Prize in Physiology or Medicine for uncovering key mechanisms of autophagy.

Yes, there really was a Nobel Prize.

But there's an important distinction.

Ohsumi did not win a Nobel Prize for intermittent fasting.

He didn't prove that fasting for exactly 16 hours activates a magical cellular cleaning cycle.

The Nobel Prize recognized his discoveries about how autophagy works.

The fasting connection came partly from the fact that nutrient deprivation is one of the conditions that can influence this cellular recycling process.

That's still fascinating.

We just don't need to add anything to it.

This is one of those places where the internet likes a much cleaner answer than science can currently give us.

You've probably seen charts claiming:

12 hours: this happens.

16 hours: autophagy begins.

24 hours: now you're really cleaning house.

Human biology isn't quite that punctual.

Much of what we know about fasting and autophagy has historically come from cells and animals. Measuring the process in living humans is much harder.

But research is moving.

A 2025 exploratory study followed 121 adults with obesity and found evidence suggesting intermittent time-restricted eating may influence autophagic activity after six months. The findings were interesting, but the researchers also emphasized that more work is needed.

So yes, there is a real relationship between nutrient availability and autophagy.

What we don't have is a universal stopwatch telling every person exactly when some cellular cleanup switch flips.

Autophagy is also a normal process happening in the body already.

You don't unlock it like a secret level in a video game.

Potentially, yes.

And we don't have to oversell it for that to be interesting.

Research suggests time-restricted eating and other forms of intermittent fasting can help some people with weight management and certain measures of metabolic health, particularly among people with overweight or obesity.

Sometimes there's an incredibly practical explanation too.

If your kitchen closes after dinner, you may simply stop eating the random handful of crackers at 10:37 p.m.

A defined eating window can also make eating feel simpler for some people.

No counting every calorie.

No complicated meal system.

Just:

I eat during these hours.

But fasting isn't automatically superior to every other way of eating, and restricting your eating window doesn't make the food inside that window irrelevant.

Timing matters.

So does what you eat.

This is probably my least favorite thing wellness culture does.

We discover something potentially useful and immediately ask:

How much further can I take it?

If 14 hours might be beneficial, maybe 18 is better.

If 18 is good, what about 24?

Then somebody online hasn't eaten since Tuesday and suddenly your perfectly reasonable overnight fast feels inadequate.

There is no medal for having the shortest eating window.

For some people, time-restricted eating fits naturally into life.

For others, it creates headaches, irritability, low energy or an unhealthy preoccupation with food.

And fasting isn't appropriate for everyone. Pregnancy, breastfeeding, diabetes and certain medications or medical conditions can change whether fasting is appropriate. Anyone with an eating disorder or history of disordered eating should be particularly cautious.

Your body and circumstances still matter.

I find it interesting that modern fasting focuses so heavily on what happens inside the body.

Insulin.

Ketones.

Metabolism.

Autophagy.

Those are worthwhile questions.

But people were fasting long before we could measure any of them.

They understood fasting through a completely different lens.

What happens when I deliberately go without something?

What does hunger make me notice?

What am I making room for?

What does it mean to practice restraint when I could simply eat?

Science has added another fascinating layer to that story.

It hasn't necessarily replaced the older ones.

Fasting wasn't invented by the wellness industry.

Neither was going without breakfast.

What changed was our ability to look inside the body and begin understanding what happens when food isn't constantly coming in.

And somewhere in that story is a Japanese scientist staring at starving yeast cells and discovering something remarkable about the way cells recycle themselves.

A discovery that eventually earned a Nobel Prize.

Not for skipping breakfast.

Not for 16:8.

Not for proving that longer fasts are better.

For helping us understand one of the extraordinary systems cells already possess.

Thousands of years before we understood any of that biology, people were fasting anyway.

For faith.

For discipline.

For reflection.

For reasons bigger than the number on a scale.

Maybe modern science hasn't made fasting a new idea at all.

It's simply allowing us to see an old practice differently.

Let's make sense of it.

-Tami