DR MICHAEL MOSLEY: Even if you’re watching your waistline, you don’t have to starve for 36 hours like Rishi Sunak to reap the rewards of fasting

Whatever your view of his politics, when it comes to food the Prime Minister’s self-discipline is remarkable. Apparently, Rishi Sunak starts his week — every week — with a 36-hour fast: he stops eating at 5pm on a Sunday and consumes only black tea, coffee or water until 5am on a Tuesday.

Even though I’m a veteran faster, I’m impressed. Not so much by the fact that he embraces fasting; there’s plenty of research to show that if you’re otherwise healthy, there’s much to be gained by giving your body an extended break from food — and plenty of people now do this.

But few of us have the willpower to deny ourselves food for as long as he does.

I’ve tried pretty much every kind of fast and I’ve found that going for more than 24 hours without food is tough. (I’m also not sure it’s the best way to get the benefits of fasting, but more on that later.)

A few years ago, I completed a four-day fast for a TV documentary. It involved just water, sugar-less black tea and coffee, and one measly cup of 25-calorie soup a day.

It was tough, but effective health-wise: after four days I lost 3lb in weight, a significant portion of which was fat. My blood sugar levels also fell substantially, as did other biomarkers, such as insulin-like growth factor 1, linked to cancer.

Despite the benefits, I’m in no rush to do a prolonged fast again. I wasn’t as hungry as I expected and didn’t feel faint, but I was distracted by feeling uncomfortable and out of place. So hats off to Rishi for putting himself through a big fast every week.

Indeed, you could be forgiven for thinking that Mondays might not be the best day to ask Rishi to make crucial decisions about running the country if there’s a chance he may be preoccupied with hunger pangs.

But there is evidence that, when you get used to it, fasting can improve focus. Professor Mark Mattson, a neuroscientist at Johns Hopkins School of Medicine in New York, told me that our ancestors had to cope with periods without food, during which time they would have needed to be highly focused on the best way to get the next meal.

The theory that the fasting state triggers a heightened level of concentration is one reason why it really took off in the tech world a few years ago. That may be one of the reasons why Rishi does it.

People have been fasting for centuries for religious reasons — but increasingly research backs the health benefits, showing that the metabolic changes that occur when you give your body a rest from food can be beneficial.

A study by Harvard Medical School in 2020 found it can enhance the body’s defence against oxidative stress (damage caused to the cells by factors such as smoking and pollution).

Fasting also helps improve blood sugar control and can lower cholesterol levels and blood pressure.

It may also help brain function, with some studies suggesting it boosts the growth of new cells in the hippocampus, an area of the brain associated with learning and memory. Most impressively, it reduces chronic inflammation, which is not only linked to conditions such as arthritis, but many of the other diseases of ageing, such as heart disease and dementia.

Last week a study by Cambridge University showed that when volunteers were restricted to eating 500 calories a day for two consecutive days, the levels of arachidonic acid in their blood rose, which in turn helped reduce inflammation.

As well as lowering inflammation, another benefit of fasting is it gives your digestive system a break from food; this triggers your body to begin the important process of cellular ‘spring cleaning’, where cells are broken down and recycled.

Last but by no means least, fasting encourages your body to switch from burning sugar to burning fat as fuel — which is great news if you want to shed excess weight. A review of studies, published in the journal Nutrition Reviews in 2015, found that a one-day fast, once a week, for 12 to 24 weeks, reduced body weight by up to 9 per cent.

But most fasting research has been done on alternate day fasting, intermittent fasting (such as my 5:2 regimen), or time-restricted eating (TRE), where you eat within a certain window — for instance, you may start with a 14-hour ‘fast’, and only eat in a ten-hour window, then gradually extend it to a 16-hour fast, then perhaps 18 hours.

And when it comes to fasting, you can have too much of a good thing. Rishi’s 36-hour fast is just too tough for most people. It’s certainly not suitable if you’re pregnant, breastfeeding, under 18, have a chronic disease or history of disordered eating — and talk to a GP first if you have diabetes.

The eminent ageing expert, Professor Valter Longo, once told me: ‘A prolonged fast is an extreme intervention. If it’s done well, it can be very powerful in your favour. If it’s done improperly, it can be very powerful against you.’

There are, of course, lots of different ways to fast.

Go to a fasting clinic in Germany and you will probably be fed around 200 calories a day in comfortable surroundings. In Russia you get nothing but water, cold showers and exercise. But it doesn’t have to be that tough to be effective.

If you’re otherwise healthy, some form of fasting is a very good idea. And it’s great to know you don’t have to go full Rishi to achieve the benefits.

We must be brave enough to call out bad behaviour 

Earlier this week I was standing in a very long queue, patiently waiting, along with hundreds of others, to pass through passport control and enter France.

At one point I saw a couple of young men barge straight to the front of the queue. A few people tutted, but only one woman was brave enough to harangue them. But they ignored her and got away with it.

This, sadly, is all too common. I was too far away to join in, but I’d like to think I would have backed that woman. And that, according to a recent study by Bath University, is important — because if we don’t speak up to support the lone voices of people who confront bad behaviour, that leads to bad behaviour being normalised. 

Published in the British Journal of Social Psychology, the research involved showing volunteers scenes of anti-social behaviour — in some cases the people behaving badly were confronted and this was supported by other bystanders; in other cases, the confronter got no support. The volunteers were then asked what they thought — when there was no support for the confronter, they assumed this meant the behaviour they’d just witnessed wasn’t that bad.

As researcher and behavioural scientist Anna Tirion pointed out: ‘If no one says anything, it chips away at social norms that protect being kind and not causing harm. Over time people start to think a particular [antisocial] behaviour doesn’t matter.’ It takes courage to confront bad behaviour, but she suggests ways to safely do so and how to support those who are prepared to stand up and stand out.

‘It depends on the situation,’ says Anna Tirion. ‘If your face is visible to everyone, such as on the Zoom call we simulated in one of our studies, simply nodding might be enough to send that supportive signal. Otherwise, a verbal expression of support like ‘Yeah, you’re right’ should do it.’

She adds: ‘If you’re physically some distance away from the confrontation, you might want to go and stand next to the confronter before you say something so your whole body language expresses that support — if you feel safe to do so.’