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How fasting shocks the body into being healthier

Probably best not to think too much about food when fasting for days at a time.

Probably best not to think too much about food when fasting for days at a time. Photo: Getty

When we humans were on the primeval plains, hunting and scavenging, we went days without food.

New research suggests that we not only managed this deprivation, but thrived in the short term.

How does this relate to humans today?

What our knuckle-dragging selves perceived as going hungry, we call fasting.

And in recent years many of us have adopted fasting to lose weight and improve our metabolic health.

Or at the least we’ve given it a go. But most of us are not that keen on fasting for days at a time. It’s too hard.

So, instead, many people have adopted ‘intermittent fasting’. This is where we only fast in a window of hours during the day.

Some adopt the 5-2 method: Eating five days, fasting for two with limited calories.

Research is finding health benefits to this approach, particularly as a protection against type 2 diabetes and other metabolic issues. See our 2021 report here.

And for those who stick at it, there is weight loss to be had.

But it tends to happen slowly. Which is healthy if not exciting.

But a lot isn’t known about what goes on at a molecular level when we fast. What are the benefits we don’t know about? What are the hazards?

How the body responds when we go without food

New research from Queen Mary University of London has found that the body “undergoes significant, systematic changes across multiple organs during prolonged periods of fasting”.

In other words, the body adapts when there’s no food to be had. And many of these adaptations are good for us.

“Potentially health-altering changes” is how the researchers describe it.

But they only start to kick in when you’ve gone three days without food.

How does that help most of us?

The researchers say their findings “provide a road map for future research that could lead to therapeutic interventions”.

This would include people who may benefit from fasting but cannot undergo prolonged fasting.

How so?

The insights “could lead to the development of fasting-mimicking treatments for individuals who cannot undergo traditional fasting, offering new avenues for managing various health conditions”.

A fast-mimicking diet tricks the body into thinking it’s going without food.

The reported benefits are astonishing. Read our report from 2022 here. And read about the latest research, published this week, here.

The new study

According to a statement from Queen Mary University: The researchers followed 12 healthy volunteers taking part in a seven-day, water-only fast (which should only be attempted under medical supervision).

The volunteers were monitored closely to record changes in the levels of about 3000 proteins in their blood before, during and after the fast.

As expected, the researchers observed the body switching energy sources – from glucose to fat stored in the body – within the first two or three days of fasting.

The volunteers lost an average of 5.7 kilograms of both fat mass and lean mass. After three days of eating after fasting, the weight stayed off.

But get this: The loss of lean (muscle) was almost completely reversed, but the fat mass stayed off.

For the first time, the researchers observed the body undergoing distinct changes in protein levels after about three days of fasting.

This indicated a whole-body response to complete calorie restriction.

Overall, one in three of the proteins measured changed significantly during fasting across all major organs.

These changes were consistent across the volunteers, “but there were signatures distinctive to fasting that went beyond weight loss, such as changes in proteins that make up the supportive structure for neurons in the brain”.

In other words, the brain gets a boost when the body is under duress.

Previous studies have reported positive changes in mood and perceived work performance among short-term fasting people.

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