How intermittent fasting may protect brain health and help extend longevity – expert tips on how to begin and how long to fast for

“We found that indeed it was effective.”

Mark Mattson is a professor of neuroscience at Johns Hopkins University.

Scientific evidence of the benefits of intermittent fasting continues to grow. An October 2023 study conducted by the University of California San Diego in the US found that time-restricted feeding “rescues brain pathology and improves memory in mouse models of Alzheimer’s disease”.

Time-restricted feeding, or intermittent fasting, has gathered a growing following, especially in the past decade. It comes in a variety of guises: the 16:8 method, sometimes called lean gains, when you fast for 16 hours of the day and consume all your calories within an eight-hour window, so from noon to 8pm, say.

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Then there’s the 5:2 diet, in which you eat normally for five out of seven days in the week and restrict your calories to about 500 for the other two non-consecutive days.

The eat-stop-eat approach describes a 24-hour fast once or twice a week, so from supper one day until supper the next, for example.

There’s the alternate-day fast, with the clue in the name – you fast every other day.

And finally, there’s the more extreme “warrior diet” – fasting for 20 hours every day and eating a big meal in a brief window in the evening.

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Mattson’s personal approach is a variation on the 16:8 – the 18:6.

“I do not eat breakfast, I exercise in late morning, and I eat all of my food within a six-hour time window, between noon and 6pm.”

A reference to an early study on intermittent fasting was startling: it reported that the average lifespan of rats on a programme of alternate-day feeding increased by more than 80 per cent.

The cover of Mark Mattson’s book, The Intermittent Fasting Revolution.

But why is eating like this any better than eating a diet that begins with breakfast at 8am and ends with dinner 12 hours later, the way I eat – the way most of us do? And why, especially, when I have a healthy diet, with lots of fibre, five servings of vegetables a day and few ultra-processed foods?

The benefits of intermittent fasting go beyond what can be achieved with a healthy diet alone, says Mattson, who in 2022 published The Intermittent Fasting Revolution. This is especially the case especially where the brain is concerned.

Mattson explains why. Early in the development of Alzheimer’s, he says, “neurons battle to use glucose because they develop insulin resistance”. But these cells can still use and function well on the ketones which our bodies produce in a state of fasting, and ketones are “a more efficient fuel and also result in less oxidative stress/free-radical production”.

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In addition to prompting the production of a more efficient brain fuel, fasting leads to autophagy – from the Greek auto, self, and phagy, to eat (so essentially eating oneself) – which on its own may help to reduce the build-up of the toxic amyloid protein plaques, the pathological marker of Alzheimer’s , and could protect neurons from the stress of this protein build-up.

Fasting – and those resultant ketones – also stimulates brain cells to produce a protein called BDNF (brain-derived neurotrophic factor), says Mattson, which enhances learning and memory and the formation of new synaptic connections between neurons.

It also helps rid neurons of a build-up of molecular “garbage” by stimulating that all-important autophagy.

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Importantly, intermittent fasting can have anti-stress and anti-inflammatory effects on the brain – and both stress and inflammation are known to contribute to brain ageing.

To protect my brain from the ravages of the dementia my mother endured, I will do almost anything. But as a “grazer” who eats frequently at irregular intervals, I am not used to, or happy, with long windows without food. I feel “hangry” and faint; I get headaches.

The reason I might feel like that, says Mattson, is that it takes time – typically several weeks – “for your organ systems – including your brain – to adapt to an intermittent-fasting eating pattern. But you will definitely adapt, though perhaps with a little encouragement,” he promises.

How to approach intermittent fasting

1. Start gradually

Many experts advocate starting by building on your natural overnight fast, from a more usual 12-hour fast up to the 16:8, adding an hour or two to your fast every few days, eating breakfast as late as you can.

This go-slow approach will help you ease into fasting, Mattson says.

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2. Eat healthily

Don’t fill your stomach in those six or eight hours with empty calories and fast food. Aim for the most nutrient-dense foods.

If you are packing your meals into an ever decreasing window, make sure you pack them with flavour and make every calorie count.

3. Exercise lightly to start

Avoid strenuous exercise until you are comfortable fasting. Yoga is fine in the early experience of fasting; a run is probably not.

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