Professor Cynthia Kenyon, a US genetisist, has discovered that the carbohydrates we eat like bananas, potatoes, bread, pasta, and cakes directly affect two key genes that govern youthfulness and longevity.

But what Professor Kenyon found out was why ­drastically reducing calories has such a remarkable effect.

She discovered that it changed the way two crucial genes behaved. It turned down the gene that controls insulin, which in turn switched on another gene, which acted like an elixir of life.

‘We jokingly called the first gene the Grim Reaper because when it’s switched on, the lifespan is fairly short,’ she explains.

The ­second ‘elixir’ gene seems to bring all the anti-aging benefits.

Professor Kenyon has changed her diet as a result of her research.

‘Carbo­hydrates, and especially refined ones like sugar, make you produce lots of extra insulin. I’ve been keeping my intake really low ever since I discovered this.

‘I’ve cut out all starch such as potatoes, noodles, rice, bread and pasta. Instead I have salads, but no sweet dressing, lots of olive oil and nuts, tons of green vegetables along with cheese, chicken and eggs.

‘I’ll have a hamburger without a bun and fish without batter or chips. I eat some fruit every day, but not too much and almost no processed food. I stay away from sweets, except 80 per cent chocolate.’

She is adamant it will be well worthwhile. ‘You could have two completely different careers if you could stay healthy to 90,’ she says. ‘How fascinating that would be.’

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Mr. Bruening also sums up what is needed to live a long healthy life very clearly:

* Be good to everybody. The more you do for others, the better you’ll help yourself.
* Everyday is a good day, and make it that way.
* Watch your diet and avoid overeating.
* Keep the mind and body busy.