It's 6.30pm, and so far today Dave Fisher has eaten 150g of prawns, a skinless chicken leg, 50g of raw peas, and a few handfuls of blackberries, strawberries, blueberries and nuts. Dinner is yet to come, and will consist of a lean chicken breast and a small salad. In total, he will have ingested around 1,600 calories, perhaps a 1,000 fewer than a typical Western man of similar height and age.
Fisher, 51, is not trying to lose weight, though weight loss is the inevitable result of the dietary regime he began 20 years ago. At 5ft 10in and 10st 8lb he is lean rather than skinny and says he appreciates food far more than he did when he was eating a lot more of it. He eats so little every day because he wants to be healthy well into old age, and because he thinks it could be the key to unlocking 20 or 30 years of extra life.
"There are two goals to a calorie-restricted diet," says Fisher. "One is maximum lifetime expansion. The other is an improvement in health in the meantime, and reducing the chances of succumbing to the diseases of ageing – heart disease, cancer and so on. I think it's worth doing for either goal."
Fisher is one of a growing number of calorie restrictors who believe, to put it simply, that less food can equal more life. Calorie restriction (or CR) may sound faddy and Californian but it has certainly piqued the interest of scientists. Last week, scientists announced the conclusion of a 20-year study by a team at the University of Wisconsin on rhesus monkeys. It is the best known of a plethora of animal experiments that are testing the claim that very low-calorie diets can improve health and extend life. And like most of them, it has produced striking results in their favour.