University debate: "Carbs are the body's preferred fuel. Ketosis is the emergency generator." Dietician: "Give the body carbohydrate and fat together and it burns the carbohydrate first. That's what preferred means." Anthropologist: "And if I add a whisky?" Dietician: "It burns the alcohol before anything." Anthropologist: "So whisky is the body's preferred fuel." Dietician: "Obviously not. Alcohol goes first because the body can't store it and can't leave it lying around." Anthropologist: "Good. Hold on to that. How much carbohydrate can you store?" Dietician: "About 500 grams. Liver and muscle." Anthropologist: "2,000 calories. One day. And fat?" Dietician: "It varies." Anthropologist: "A lean person carries 80,000. Two months. So the body burns first whatever it has least room for. You've just explained that to me using whisky, and then called it a preference when it's bread." Dietician: "The brain needs glucose. 130 grams a day." Anthropologist: "On your diet. Offer it ketones and it takes up to two thirds of its energy from them, and the liver makes what's left. How much glucose is in your whole bloodstream at this moment?" Dietician: "Around 5 grams." Anthropologist: "A teaspoon. Much more than that damages blood vessels, so the body drops everything to clear it. I've seen bouncers treat people that way. I wouldn't call them preferred." Dietician: "Ketosis only appears when you're starving. That is an emergency." Anthropologist: "It appears within a day of the carbohydrate running out, fed or not. Where was the starch in northern Europe in January, for half a million years? You've filed every winter our species ever had under emergency." Dietician: "Nobody is in ketosis as a normal state." Anthropologist: "Every newborn is. Within days of birth, on breast milk, with half its calories from fat. The fastest brain growth in nature runs on your back-up system." Dietician: "Then why do people feel dreadful when they cut carbs?" Anthropologist: "For about a week. Take a leg out of plaster after forty years and it won't feel marvellous on the stairs either." Moderator: "Closing statements." Anthropologist: "The mains runs out by tomorrow lunchtime. The generator has two months in the tank and was switched on at birth. I'd ask which one the house was built around."