“This is the beginning of something . . . it could be genuinely revolutionary.” Horizon’s “Eat, Fast and Live Longer” was an hour long documentary presented by the doctor and producer Michael Mosley.1 He had wanted to find out how to “live longer, stay younger, and lose weight in the bargain.”

The programme began with the world’s oldest marathon runner finishing in London—and gave the implication that he had reached the age of 101 in full health, with no signs of heart disease and taking no drugs, because of his diet, which was mainly fresh fruit. We can’t alter our genes, said Mosley, but we can choose what we eat. He said that in the United States “truly remarkable” research was linking diet and longevity.

During the great depression, he explained, life expectancy actually rose. Meanwhile in recent animal experiments severe food restriction had been found to increase life expectancy. With obesity and type …