In 1977 a young chemist who went on to lead the first women up Annapurna proved that the chemical America had been putting on its children's pyjamas to stop them catching fire could cause cancer, and it had been going to bed with American children for years. Her name was Arlene Blum. In 1972 the United States made it law that children's sleepwear had to resist flame. There was already a fabric that did that on its own: wool chars and puts itself out. The industry kept its cheap synthetics and treated them instead, and the chemical it chose was called Tris. Blum was a doctoral student at Berkeley with a habit of climbing very large mountains between experiments. She worked with the biochemist Bruce Ames, who had invented a quick test for whether a chemical damages DNA, and they put Tris through it. It failed. It was already known to cause cancer in animals, and it did not stay on the cloth: children who slept in it passed its breakdown products in their urine. The paper went into Science in 1977, and that April the government banned Tris-treated children's clothing. The industry swapped in a close relative, chlorinated Tris. Blum and Ames showed that one was probably carcinogenic too, and it came out of children's sleepwear as well. Then she went climbing. In 1978 she led an all-women team to the summit of Annapurna, the first Americans ever to stand on it, and two of her climbers, Vera Watson and Alison Chadwick-Onyszkiewicz, died on the mountain. Decades later she came back to Berkeley and found high levels of flame retardants in the blood of her own cat. Then she found that the chlorinated Tris taken out of children's pyjamas had gone into the foam of the country's sofas and into baby products, because of a 1975 California furniture rule demanding foam that could survive a naked flame for twelve seconds, and the cheapest way to pass it was to soak the foam in chemicals. It took until 2013 to get the rule changed. "Our work has shown that there's not an additional fire-safety benefit," she said. Wool never needed any of it. It has been putting itself out since the first sheep was shorn.

1774: they blew tobacco smoke up drowning victims' backsides to revive them, and the kits hung along the Thames like lifebuoys. 1863: they sold cocaine wine as a daily tonic, and a pope pinned a gold medal on it. 1898: they sold heroin as a cough medicine, and spooned it into coughing children. 1918: they sold radium water as a health drink, and the millionaire who drank 1,400 bottles was buried in a lead-lined coffin with most of his jaw gone. 1921: they put lead in petrol, and Britain kept it in the pumps until 2000. 1930s: they X-rayed children's feet in shoe shops, and kids queued to watch their toes wiggle on the screen. 1940s: they rubbed mercury teething powder into babies' gums, and about 1 in 500 of those babies was poisoned. 1946: they sold cigarettes on the line that more doctors smoked their brand, and put a man in a white coat on the advert. 1949: they gave the lobotomy a Nobel Prize, and doctors went in through the eye socket with an ice pick. 1952: they sold a cigarette filter made of asbestos as the greatest health protection in smoking history, and smokers drew it into their lungs with every puff. 1957: they sold thalidomide to pregnant women for morning sickness, and around 10,000 babies were born with missing or shortened limbs. 1960s: they sold margarine as the heart-healthy fat, and spread trans fat on a generation's toast. 1996: they sold OxyContin as barely addictive, and started an overdose epidemic. 1999: they sold Vioxx for sore joints, and pulled it five years later after tens of thousands of heart attacks. 2026: they're selling seed oil as the heart-healthy fat, and it's in almost every packet in your kitchen. Every one of these came with an expert's blessing and the same total certainty. The people telling you which fat to fear today sit in the same chairs as the ones who put radium in the water and a doctor on the cigarette packet, and they're every bit as sure. "The experts recommend it" has the longest body count in medicine.

Customer: "Your pork chops any good? The ones I get are like cardboard." Butcher: "They're like cardboard because the pig was built to order." Customer: "Built?" Butcher: "Bred. In the seventies the advice came down that fat was killing people, so the pig industry bred the fat off the pig. Took about twenty years. Backfat halved. A 1970s chop had a thumb of fat on the edge and marbling through the middle. Yours has a rind of nothing and a muscle that's never been near a lard cell." Customer: "That sounds like progress." Butcher: "Taste it and tell me. The fat was the flavour. The fat was what stopped it drying out in the pan. They bred the dinner out of the animal to meet a guideline, and then wondered why nobody cooks pork any more." Customer: "My mum's chops were lovely." Butcher: "Your mum's chops came off a different pig. Same breed name, different animal underneath. They changed the pig and never changed the recipe, so your mother's twenty minutes under the grill turns a modern chop into a roof tile." Customer: "Can you still get the old sort?" Butcher: "Rare breeds. Tamworth, Gloucester Old Spot, kept by people who ignored the memo. Slower to grow, more fat on, and a chop that tastes like 1975. That's what this is." Customer: "Why did the industry go along with it?" Butcher: "Because the supermarket buys the lean one. And the supermarket buys the lean one because a man in an office told the country fat was poison. Fifty years on the country's fatter than it's ever been and the pig's thinner than it's ever been. One of them got the advice wrong." Customer: "Four of those, then." Butcher: "Leave the rind on, let it brown, and don't apologise to anyone for the fat. The pig had it put back on purpose."

Customer: "Why did mutton disappear? My gran talked about it like it was Sunday itself." Butcher: "Because you stopped wearing wool." Customer: "What's wool got to do with it?" Butcher: "Everything. For a thousand years this country kept sheep for the fleece. The wool paid the rent. A ewe was clipped every summer for six or seven years, and when she'd given her last fleece she gave you Sunday dinner. Every leg of mutton was a sheep that had already paid for herself." Customer: "And lamb?" Butcher: "A luxury. You'd no more eat a lamb than burn a five-pound note. That's seven fleeces walking into the oven." Customer: "So what changed?" Butcher: "The jumper went plastic. From about 1960 a fleece was worth less every year until it was worth nothing, and today a farmer gets roughly what it costs him to shear her. Nobody keeps a sheep seven years to collect two pound a time, so they bred her for the one thing left that paid." Customer: "Meat." Butcher: "Fast meat. Lambs that fatten by four months and leave before they've cost anything. Inside one generation the sheep went from a wool animal with a dinner at the end to a dinner in a hurry that grows a coat nobody wants." Customer: "And the old ewes?" Butcher: "Still coming off the hill every autumn, and still the best eating in this shop. Five years of grass and heather in the fat, meat the colour of beef, and she's never seen a bag of feed in her life. Grass-fed is the label people pay double for on a steak. On her it's just Tuesday." Customer: "Why's she half the price, then?" Butcher: "Because nobody asks. A leg feeds eight, low oven, four hours, and the gravy off it will make you forget lamb was ever invented. The old boys who come in for it never bother with anything else." Customer: "My gran used to say the fat was the point." Butcher: "Your gran was right about most things. The jumper went to plastic and the roast went with it, and nobody noticed they were the same sheep. You can undo the whole thing in one shop. I've got the leg. The jumper's your problem."

In Britain your cat has a legal right to the diet her body was built for, and you have a leaflet telling you to eat the opposite of yours. The law says a cat must be given a suitable diet, and a suitable diet for a cat is meat, because she cannot make her own taurine and goes blind without it. The law says a zoo lion must be fed like a lion, so the keepers throw in whole carcasses with the bone and the hide still on. The law says a zoo gorilla must be fed like a gorilla, so when the biscuits made them fat the keepers took the biscuits away and gave them leaves. The law says a dog must be given a suitable diet, and an owner who fails it can be prosecuted. The farm vet balances a dairy cow's ration to the gram, because too much grain twists her stomach. The horse is kept on grass and hay, because one sack of oats too many cripples him. Every one of those animals is fed by the same rule, that a body should get what its species evolved to eat. Then there is you. Your official plate is a third starch, a third fruit and vegetables and a corner for meat, drawn by a committee, and the hospital, the school and the care home all serve it. No law says a human must be fed like a human. Every animal in Britain is protected from the wrong diet except the one who wrote the protection.