The most detailed description of an English peasant's larder was written by a man who lived among them in the 1370s, and there is no meat in it. William Langland, Piers Plowman. Hunger arrives at the ploughman's door in early summer and demands to be fed. Piers lists everything he has until the harvest comes in: - 2 green cheeses - A little curds and cream - An oat cake - 2 loaves of beans and bran, baked for his children - Parsley, leeks and cabbages Then he lists what he has not got, and swears to it: - No salt bacon - No eggs to fry - No chickens - No geese - No pork He owns a cow and a calf. They are for milk and for rent, and they are not for eating. Piers is no beggar. He is the hero of the poem, the honest working ploughman with his own half acre. And this is the 1370s, the decades historians call the golden age of the English labourer, when wages were the best they had been in 300 years. Langland then complains about the labourers who have done well out of the plague. They have started turning their noses up at cabbage and yesterday's pottage, and demand fresh meat, hot, fried or baked. Every source agrees on this. The medieval poor ate plants because plants were what they had, and the moment a penny was spare it went on meat.

Americans of the 1800s ate meat three times a day in quantities that would get a modern dietitian struck off, and their doctors described heart attacks as a rarity. The folk memory says otherwise. Pioneers lived on cornbread, beans and hardtack, meat was a Sunday luxury, and it is only fat modern America that gorges on red meat and pays for it in the cardiac ward. That is the story underneath every guideline: go back to eating like your ancestors, meaning less meat. Their ancestors kept diaries. When Lewis and Clark crossed the continent between 1804 and 1806, the Corps of Discovery ran on game. Clark, 13 July 1805: "We eat an emensity of meat." He gave the daily requirement for the party as 4 deer, or an elk and a deer, or 1 buffalo. When the hunting was good it came to as much as 9lb a man a day, for men hauling boats upstream. The tally for the whole journey runs to 1,001 deer, 375 elk, 227 bison, 43 grizzly bears and 190 dogs, which they bought from the tribes and, Clark excepted, came to prefer. The expedition carried an emergency food, 193lb of dried portable soup, and the men loathed it. The one time the whole party went down sick was in September 1805, on the far side of the Rockies, when the game ran out and the Nez Perce kindly fed them dried salmon and camas root. The captains' journals spend days on the consequences. Sacagawea, about 17 and carrying a baby on her back, ate what the soldiers ate the whole way there and the whole way home. The men who supplied the fur trade lived the same way on wages: the Hudson's Bay Company's standard daily ration for a working man on the plains was 8lb of fresh buffalo meat. Settled America ate the same way with cutlery. Pork was the national staple, salted down by the barrel. By the 1840s Cincinnati was packing so many hundreds of thousands of hogs a year that the country called it Porkopolis, and after 1865 the Union Stock Yards in Chicago did the same for beef on a scale the world had not seen. Frances Trollope, who spent two years living in Cincinnati and never forgave it for the pigs in the streets, reported in 1832 that ham and beefsteaks appeared "morning, noon and night", alongside an extraordinary amount of bacon. When Wilbur Atwater, the founding father of American nutrition science, ran the first proper dietary surveys in the 1890s, he found the average American eating 147lb of meat a year. The average Italian ate 24. Atwater found labourers having beefsteak for breakfast and put the vigour of the American workman down to it. All of it was cooked in lard, butter and tallow, because there was nothing else to cook in. And William Osler, the most celebrated physician in the country, writing the standard medical textbook in 1892, described angina as a rare disease. The 20th century is where the lines cross. Beef eaten per head peaked in 1976 and has since fallen by about 40%. Butter and lard collapsed. Vegetable oil went from nothing to the biggest single item in the nation's fat supply, and chicken breast replaced the steak. Americans, in other words, did what they were asked. They followed the advice for more than 40 years, more faithfully than any population has ever followed a diet. Frances Trollope would not recognise a single thing on the modern plate. She would not recognise the people sitting in front of it either.

Journalist: "You're selling raw milk at the farm gate. Unpasteurised. That's a public health hazard." Dairyman: "What's pasteurising for?" Journalist: "Killing dangerous bacteria." Dairyman: "From where?" Journalist: "The milk." Dairyman: "The muck, the bucket and the cow. It came in when town milk was from sick cows in sheds behind the pub, carted warm for a day and topped up at the pump. They couldn't clean the dairy, so they cooked the milk." Journalist: "And you think you're above all that." Dairyman: "I think I'm inspected. The herd's TB tested. A man comes twice a year and goes through the parlour with a torch. The milk goes to a lab 4 times a year. One bad result and I'm shut that afternoon." Journalist: "People have been made ill by raw milk." Dairyman: "By dirty milk, same as dirty anything. 2 summers ago near 300 people in this country went down with E. coli. It was lettuce, out of a sandwich. How's the campaign against salad going?" Journalist: "Salad doesn't carry the same risk." Dairyman: "Salad doesn't carry a label. Every bottle I sell has a warning on it by law. Find me that on an energy drink, a vape or a bag of rocket." Journalist: "So you accept it's risky." Dairyman: "I accept I'm the only thing in your fridge that's been made to say so. My customers drive 40 minutes past 3 supermarkets, read the warning and buy 6 litres. Best-informed shoppers in Britain." Journalist: "The experts advise against it." Dairyman: "The experts advised margarine. People round here have drunk this for a few thousand years. I'll give the experts time to settle down."