The one change that matters most

If you ignore everything else we ever tell you, do this one thing. Seed oils.

Sunflower, rapeseed, soybean, corn oil, and the blends sold as vegetable oil. Seventy years ago almost nobody cooked with them, because they are hard to make. Most of them are not pressed the way olive oil is. Making them takes heat, solvents, bleaching and deodorising, and the result is an oil that did not exist in a kitchen anywhere in the world until the last century. Now it is in almost everything on a shelf, from the bread to the mayonnaise to the granola with "wholesome" written on the front.

Bear calls it the most successful substitution in the history of food, and he means it as an accusation. Butter, dripping, olive oil and tallow were swapped out of our diets on advice that is now argued over by the very people who gave it, and most of us never noticed the swap happen.

The fix is a cupboard clear-out. Butter, ghee, olive oil, and the fat that comes off the meat. Read the back of the packet on anything in a box, and if the oil is in the first five ingredients, that is the thing to put back. Fake milk gets the same treatment: oats and water and a gum and, yes, an oil.