In June 1965 a 27-year-old Scot weighing 456lb stopped eating, didn't start again for 382 days, and the fat he was carrying kept him alive for every one of them. Angus Barbieri worked in his father's fish and chip shop in Tayport, across the Tay from Dundee. He had eaten his way past 32 stone. He checked himself into Maryfield Hospital for what his doctors intended as a short fast. It went well. He felt fine. He asked to carry on. The doctors agreed, warily, and let him go home, provided he came back in regularly for blood and urine tests. He lived on tea, coffee, sparkling water and vitamins. No food. A week became a month. A month became a season. The weight came off at about three-quarters of a pound a day. Day 100 came and went, then 200, then 300, with the hospital checking his blood every step and waiting for something to break. Nothing did. For long stretches his blood sugar sat at around 30mg per 100ml, about a third of normal, the kind of reading that has junior doctors reaching for a drip. He went about his days perfectly lucid. On 11 July 1966 he sat down to his first meal in over a year: a boiled egg and a slice of bread with butter. He weighed 180lb, under 13 stone. He had lost 276lb, very nearly 20 stone, and it went into the Guinness Book of Records as the longest fast in history. Five years on he was still around 14 stone, and he lived until 1990. His doctors wrote him up in 1973 under the driest title in medicine: Features of a successful therapeutic fast of 382 days' duration. His brain kept working the whole year, which is the part the textbooks of the day had no answer for. In 1967, in Boston, George Cahill's team supplied one. They ran fine tubes into the blood vessels draining the brains of three obese patients five weeks into a fast and measured what the brain was burning. It had switched to ketones, made in the liver from body fat, as its main fuel. The organ every textbook said ran only on glucose was running on fat, and running happily. So every thought Barbieri had that year was powered by the fat around his middle. A human body carries months of fuel and a brain built to use it. It was shaped by two million years of hunts that came good one week and failed the next, and it treats an empty plate as an ordinary Tuesday. Angus Barbieri had 382 of them.