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.

‘It isn’t a diet, it’s a lifestyle’: the benefits of intermittent fasting

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.

How intermittent fasting and exercise helped Hong Kong banker lose 32kg

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.

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”.

9 intermittent fasting errors, from eating too little to exercising too much

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.

A decade of intermittent fasting – see how one health coach did it

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.

Weight loss, better skin: 7 health benefits of vegetable broth

2. Eat healthily

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