Prof Longo thinks this may be because they have learnt that they are naturally resistant to cancer and diabetes, and tend not to be terribly careful about their diets.“They smoke, eat a high-calorie diet, then they look at me and say, 'Oh, it doesn’t matter, I’m immune.’ I think they would rather take the 85-year life and do what they want than the 100-year life and have to be restricted.” Fasting lowers levels of IGF-1 and also appears to switch on a number of DNA repair genes.Although most of the great religions advocate fasting (devout Muslims finish fasting for Ramadan this weekend), I have always been sceptical about the medical benefits and followed the standard advice, namely “never skip a meal and never crash-diet”.The reasoning behind this is that people who skip meals tend to eat high-fat snacks when they get hungry, while those who crash-diet lose weight fast but what they lose is mainly water, with some fat and muscle thrown in. At this year’s event there were more than 7,000 runners aged over 50, and seven who were over 80.Oddly enough, when the mice are examined, scientists are often unable to find a cause of death. One of the links between fasting and longevity seems to be a hormone called insulin-like growth factor 1 (IGF-1).As Prof Longo explained, IGF-1 and other growth factors keep our cells constantly active.
But Prof Longo warned me that fasting is not for the faint-hearted, and is safest done in a specialised centre or under supervision.
When crash-dieters give up, as invariably they do, they pile on the pounds, mainly as fat. The most impressive competitor, however, had to be Fauja Singh, also known as “the turbaned tornado”. The Fast Diet by Dr Michael Mosley and Mimi Spencer at the Telegraph Bookshop. His lifestyle is nothing like that of the average marathon-runner.
He is a strict vegetarian, so he is not getting muscle-building protein from fish or meat.
Like his genetically engineered relatives, he should live to the equivalent of 120, maybe even 180.
Laron mice are largely immune to heart disease and cancer, and when they die it is usually of natural causes.
“This,” he proudly told me, “is a dwarf or Laron mouse.