The heart attack was first described in a medical journal in 1912, and the man who described it had trouble finding a second case. Doctors had been opening chests for 300 years. They had dissected kings, paupers, drunks and the obese, and the blocked coronary artery was a rarity you wrote up. A young Boston cardiologist started practising in 1911. He later said he did not see his first heart attack patient until 1921, and then they came in a flood. By 1950 it was the biggest killer in the United States. By 1960, in Britain. Victorian England ate butter, dripping, suet, bacon and cream, and smoked like a chimney, and the coronary ward did not exist. The Masai lived on milk, meat and blood, and the doctors who went looking in the 1960s could not find heart disease among them. So what arrived between the dissecting rooms of 1900 and the coronary care units of 1960? Crisco launched in 1911. Cottonseed oil hardened into a block that looked like lard. Margarine followed it into every kitchen. By 1960 a quarter of American fat came out of a seed press that had not existed in 1900. The seed oil goes into your blood on the LDL particle. It is the part of the particle that oxidises. The oxidised particle is what the artery wall takes in. The cholesterol was in the butter for a thousand years and the artery stayed open. Then the fat changed, and a disease nobody had heard of became the way most people die. The guideline blames the butter. The butter has an alibi going back to the Bronze Age.

In 1804 Thomas Jefferson sent thirty-three men to walk off the edge of the known map and find out whether America went all the way across. They came back two years later having lost one man, and the reason the rest lived is written in the journals in a word no dietitian uses: fat. The Corps of Discovery left St Louis in May, hauling a keelboat up the Missouri against the current, by rope, through mud to the waist. Nobody knew what was out there. The maps gave out at the Mandan villages. Beyond that was rumour: mountains that might be a day's walk across, rivers that might run to the Pacific, and animals the size of carts that nobody back east believed in. The men ate like no men have eaten since. Nine pounds of meat a day each, when it could be got. Four deer for the party, or a buffalo, every single day. Clark wrote that they consumed an immensity of meat. And by the autumn of 1805, on the high plains, they had learned the thing the plains people had always known. The buffalo in October carries inches of yellow fat down its back, and the men stripped it off and ate it before they touched the lean. They roasted marrow bones in the embers and sucked them like sweets. Charbonneau stuffed buffalo gut with meat and kidney fat and Lewis, a man who did not hand out praise, called it one of the great dishes of the frontier. They rendered bear grease into kegs and carried it over the Rockies like gold. Then came the winter on the Pacific. Fort Clatsop, rain for a hundred days, and the only game was elk, lean as rope after the mountains. The men lived on it and the journals turn dark: boils, bowel trouble, men laid flat with nothing left in them. The meat was plentiful. It was the fat that had gone. In January a whale washed up on the shore. Lewis sent a party through the surf and over a headland to buy its blubber from the Clatsop people, and when it came back he wrote that providence had been kinder to them than to Jonah, since it had sent the whale to be eaten rather than the reverse. The men came back to life on it. They crossed the Divide, found the river, saw the ocean, and walked home. One grave in 8,000 miles, three months in, a sergeant with a burst appendix. No scurvy in two years without a vegetable. The greatest expedition in American history ran on buffalo fat, bear oil, marrow and whale blubber, and its captains knew exactly what was keeping their men on their feet. Send the same thirty-three men out today with oats, lean turkey and a bag of lentils, and the only thing that reaches Oregon is the paperwork.

Six years of carnivore teaches you a second language, and half of every dinner party now needs subtitles. What I say, and what it means. "I'm not that hungry." I had 500 grams of mutton mince at lunch and food hasn't crossed my mind since. "I'll just have the steak." The biggest one. Fat on. Whatever was going next to it, put butter there instead. "I'm easy, whatever you're having." Whatever you're having had a face. "I'll eat later." Once. Enormously. Possibly standing up. "Just a black coffee, thanks." I've already had four eggs and I'm being polite. "Is there any more butter?" There is never enough butter, and we both know it. "Can I have the fat you've just trimmed off?" Yes, I'm serious, and no, it's not for the dog. "I'll bring something." I'll bring a cheeseboard and eat most of it. "No pudding for me." I had my pudding. It was the fat on the lamb. What other people say to me, and what it means. "Everything in moderation." I'm about to have a biscuit. "Where do you get your fibre?" I'm about to tell you about my bowels. "I could never give up bread." I have never tried. "Don't you miss pasta?" Please tell me you miss pasta. "Isn't that expensive?" I've never added up what I spend on snacks. "I'm on a bit of a health kick myself." There's a protein bar in my handbag. "Go on, a little bit won't hurt." I need you to eat this so I feel better about mine. "Have you tried intermittent fasting?" I skipped breakfast once in 2019 and I've been telling people since. "Doesn't it get boring?" I've had the same meal deal at my desk every weekday since the Olympics. "My doctor would have a fit." My doctor has never once asked what I eat. "I'm not judging." I'm judging. "Is that even healthy?" I've never asked myself that about my own lunch. "You'll be dead by sixty." Please don't prove me wrong in front of everyone. And one phrase that needs no translation at all, the one they land on once they've worked through the rest: "You look well, though."

In the winter of 1069 William the Conqueror put down a rebellion in the north of England by killing the animals. The people died afterwards, on their own. Three years after Hastings, Yorkshire rose against him with Danish help. William marched north, bought off the Danes, and then decided the region would never trouble him again. He did not need a battle. He split his army into small bands and sent them through every valley between the Humber and the Tees. Their orders were to destroy what kept people alive. They slaughtered the cattle, the sheep and the plough oxen. They burned the stored grain and the seed corn. They broke the ploughs. Then they left, in midwinter. A monk who wrote the history of those years, and who admired William, could not excuse it. He recorded that the survivors ate horses, dogs and cats, and then each other. Some sold themselves into slavery for a meal. He put the dead at 100,000. The corpses lay unburied on the roads, because there was no one left with the strength to dig. Sixteen years later the King's surveyors rode through the same country compiling Domesday Book. Against village after village in Yorkshire they wrote one word. Waste. William is said to have confessed it on his deathbed as the sin that weighed on him most. It became the standard method. Sherman used it in Georgia. The United States Army used it on the Plains, against the bison. Every commander who has wanted to break a people for good has understood the same thing. You do not have to fight them. You only have to get to the herd first.

Try making sunflower oil at home and you'll understand everything wrong with seed oil. To make butter, you pour cream into a jar and shake it for ten minutes. To make dripping, you roast a joint of beef. It makes itself. To make olive oil, you crush olives and the oil runs out. To make sunflower oil, you squeeze a sunflower seed as hard as you like, and nothing comes out. Corn is about 4% fat. Nobody has ever bitten into a corn on the cob and had oil run down their chin. To get oil out of seeds like these, a factory crushes them, washes them in a petrol-based solvent, cooks the solvent off, treats the oil with caustic soda, bleaches it with clay, then steams it at around 240 degrees until it stops smelling. Every fat people ate for two million years could be made with your hands, a fire and a knife. Seed oil needs a chemical plant and a fire certificate. If your great-grandmother couldn't have made it in her kitchen, it has no business in yours.

In 1931 a dentist from Cleveland found a valley in Switzerland with 2,000 people, no doctor, no dentist, no policeman, almost no tooth decay, and a cow on every hillside. Weston Price had spent his career looking at rotten mouths in Ohio and wanted to know what a mouth looked like before the shop arrived. The Loetschental had no shop. One road in, closed by snow for months. The diet was raw milk, raw butter, raw cream and raw cheese, off cows that climbed to the high pasture in June and came down in September. Rye bread was baked once a month in the village oven and eaten with cheese cut as thick as the bread. Meat was Sunday. He examined thousands of teeth with no toothbrush in the valley and found decay in 3 of every 100. The Swiss government's own records showed no death from tuberculosis in the valley at a time when it was killing the rest of the country. The first butter after the cows reached the summer grass was deep orange, and the valley carried it to church to give thanks for it. He went down the mountain to the towns the railway had reached, where the shop sold white flour, sugar and tinned food, and found rotten mouths and the tuberculosis ward. Same people. Same mountains. Same cows, a train ride apart. The entire medicine cabinet of the valley was a cow on a hill, and it ran a 97% success rate on teeth without a single qualification between them.