Increasing numbers of people in Britain seem to eat according to very clearly defined rules, from fashionable Clean Eaters to religious believers to professional sportspeople. In this third programme in the series How we Eat, Sheila Dillon talks to them about the rules they follow and why, sometimes, rules make life not only easier but more enjoyable. She meets vlogger Madeleine Shaw, an Instagram Star with 275,000 followers, whose 12-point eating philosophy includes the rule "Don't Eat Anything Beige". She talks to followers of the ancient Jain religion, who believe it's deeply wrong to eat root vegetables or anything raw. If they break the rules, there is a complex system of atonement. She visits a slimming class to discover the pleasures of eating according to a clearly defined plan and why iced Chelsea buns are evil. And she talks to professional athletes, a jockey and a boxer, about how they eat when they know that their entire livelihood depends on not gaining a single pound.