My last supper as a mortal took place on Hallowe’en at Florent, a French diner in New York’s meat-packing district. The parade was in full swing and waiters in drag served tables of clowns. Olivia Newton-John (emphasis on John) circa Physical in leggings and an off-the-shoulder T-shirt recommended the steak frites with green beans followed by cheesecake and ice cream. It all sounded good to me.

I love food and have never really taken much interest in the calories it contains. I vaguely remember that Tic Tacs have two calories (Tic Tac two) but I could be wrong and, until recently, I haven’t given a monkey’s. For the past 10 years, I have weighed 12 stone 5lb, give or take a few pounds. I’m 41, 5ft 11in and neither thin nor fat. I’m a small large. I eat an average amount for my size – about 2,500 calories a day.

My body mass index (BMI), the calculation many doctors use to assess weight, is 24.4, the high end of normal. Add a few pounds and I would be overweight but I’d have to slap on well over a stone to be “obese”. Most importantly, I weigh less than most of my male friends. Now, this laissez-faire attitude to food is going to stop. From the stroke of midnight I am going to retrain my body to live on 1,800 calories a day on a diet that, a growing body of evidence is showing, will increase my life span, reduce my chances of serious diseases like cancer and may even give me a shot at cheating death.

In 1991, Dr Roy Walford, an expert on ageing and a Korean-war veteran, was sealed inside Biosphere 2 with seven other “crew” members. Among other delights, the 3.14-acre site contained a rainforest, an 850-square-metre ocean with a coral reef, and mangrove wetlands. For two years, they were supposed to support themselves on food they would grow themselves, to test the feasibility of setting up such sites on distant planets. The crew found they could not grow enough food and the experiment almost had to be cancelled. Solving the food dilemma led to an experiment that convinced Walford he had found a way to extend human life.

Walford convinced the crew to follow a nutrient-rich diet of between 1,400 and 2,000 calories a day. Within six months the crew’s weight had, unsurprisingly, fallen 14% – but they also showed dramatic falls in blood pressure, cholesterol, blood sugar and insulin. Did the Biosphere contain the fountain of youth?

Walford certainly thought so. He was not the first scientist to investigate the anti-ageing effects of calorie restriction (CR). Studies going back as far as 1934 had shown that rats fed a severely reduced-calorie diet, while maintaining vital nutrient levels, lived twice as long as other rats. But after Biosphere 2, Walford was to become CR’s greatest proselytiser.

In his bestseller, Beyond the 120-Year Diet, Walford notes that average life spans have been increasing for the past 100 years, but humans’ maximum life span – the maximum number of years anyone has lived – has remained steady at around 110 years.

Even the Bible pegs us out at around that number. Adam may have lived for 930 years, but for the rest of us, according to Genesis 6:3, “[man] also is flesh: yet his days shall be an hundred and twenty years”.

Walford died in 2004 at the age of 79 through complications from amyotrophic lateral sclerosis (ALS), often referred to as “Lou Gehrig’s disease”. Evidence is growing that CR fights off many serious diseases that strike in middle age. Ironically, ALS is one of the few shown to have been accelerated by CR. But his book, first published in 1986, and research have inspired a hardy band of would-be immortalists.

This year, the Calorie Restriction Society annual meeting was held in San Antonio, Texas, home of the Alamo. There’s a last-ditch feel to this affair too. About 40 people, half of last year’s number, have turned up. It’s not hard to see why. Most people want to be thin, youthful and live for ever, but CR is no easy way to do it.

A week into my diet I am constantly hungry.

I plan my next meal as I eat my last. In my room there is an ad for the hotel shop: “Food so close to your suite, you can almost hear those chocolate cookies calling your name.” Man, are they calling. In New York I have been surviving on porridge, leaves and raw fish. I feel like Gollum. Round the corner from the conference venue is a joint called Fatty’s Burgers. Mmmmm.

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