Diet books come and go. The latest craze in eating plans comes from French doctor Pierre Dukan, and its followers are full of praise. "It works!" they say. "Hurrah!" Of course it works. It's protein-based and protein, unlike fats and sugars, isn't laid down as lardy slabs in the body. We use protein, not least to build muscle, or we convert it into blood glucose. It's simple science.

Nevertheless, my own favourite diet guidance doesn't come from science fact, but science fiction. Oryx and Crake, the dystopian novel by Margaret Atwood, relates the life and history of Snowman, who is slowly starving to death: "He knows that if he doesn't balance out the protein with starches and that other stuff – carbohydrates, or are those the same as starches? – he'll start dissolving his own fat, what's left of it, and after that his own muscles. The heart is a muscle. He pictures his heart, shrivelling up until it's no bigger than a walnut."

There it is, banting and its dangers, plainly and graphically explained. Atwood is an unlikely diet guru, but sound and succinct all the same.