What the Body Does When It Eats Less — I Was Sceptical for a Long Time

"Should I try intermittent fasting?"

I was sceptical about this question for a long time. I have shifted somewhat, and I want to set down what happened in between.

Why I was sceptical

Many of the people who come to me come with anxiety or with symptoms on the autonomic side. In them I often see how the body answers when blood sugar swings.

When blood sugar falls, the body sends signals such as adrenaline to bring it back. The heart runs, hands tremble, sleep grows shallow. Adding one more swing to someone already on edge was something I was wary of. (The Body Does Not Hold an Exact Number)

That thought still holds. It just was not the whole account.

There was another layer on the cell side

Studying the ageing side, I came upon this. Cells have a device that clears away what has grown old or broken inside them. It is called autophagy.

This clearing does not run all the time — it switches on and off. And what holds that switch is the cell's energy situation.

When nutrients are plentiful a pathway called mTOR switches on and halts the clearing. When energy runs short a pathway called AMPK switches on and starts it. What is striking is that the two send signals to different sites on the same protein, working in opposite directions.

A cell is set up to build while it is well fed, and to tidy when it is short.

The survival switch and the clearing switch are joined

This is the part I found interesting.

Inside the cell are proteins that decide whether it lives on or clears itself away. Bcl-2 works toward survival, Bax toward clearing.

And that same Bcl-2 is also holding autophagy down. The protein that starts the clearing, beclin-1, is ordinarily bound to Bcl-2; when stress comes that bond loosens and the clearing begins.

Living on and clearing away share the same site on the same protein. I read that as the body not treating the two separately.

In mice, lifespan increased

There is a study from 2018. In mice, weakening only the bond between Bcl-2 and beclin-1 so that the clearing ran a little more actively lengthened lifespan and reduced age-related changes in kidney and heart.

One gene was altered, only the clearing went up, and lifespan changed — as evidence of cause it is fairly strong.

They were mice, though. I would rather not blur that.

In people there is still no way to measure it

This is the weak place in the account.

There is no established way to measure how much of this clearing runs in a person. Measuring it properly means briefly blocking the breakdown step, which cannot be done in people, and it moves differently from organ to organ within the same person.

So figures of the sort "go without food for so many hours and the clearing switches on" have never been confirmed in people. Most of them came over from animal work.

And in trials with people, the ways of eating less did not differ much from one another. Dividing the hours or reducing the whole amount comes out about the same.

So where I now stand

This account joins an old idea — that a mild stress rather wakes the body's own maintenance and repair. But a condition always attaches: it holds when the stress is mild and periodic, and runs the other way when it is severe or drawn out.

So I see it this way. Rather than one way of eating less being better than another, what settles the answer is the state that person is in.

For someone on medication that lowers blood sugar, someone already underweight, someone pregnant or nursing, I do not advise it. And for someone whose blood sugar genuinely swings widely I remain wary. The reason I was sceptical at the start is still there.

What changed is only that it narrowed from "wary for anyone" to "wary for whom." I am not in the business of recommending it. With someone already doing it, or thinking of it, I would rather look together at the conditions under which they do.

When to see a doctor first

If you are on medication that manages blood sugar, speak with whoever prescribed it before changing when you eat. If cold sweats, trembling hands or a fading feeling have come while going without food, tell me that too.

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Sources

• An account that intermittent fasting does not work the same for everyone and carries risk for those who need blood sugar managed — Seoul National University Bundang Hospital
• A study in which weakening only the Bcl-2–beclin-1 bond in mice lengthened lifespan and reduced age-related lesions — Nature, 2018
• A piece setting out how two pathways working in opposite directions, when energy is short and when it is plentiful, switch the clearing on and off through the same protein — The EMBO Journal, 2011

Written by Dr. Heo Ji-young (Ph.D. in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)