But it's silly to keep chomping away on cakes and crisps and fizzy pop and getting bigger and bigger. Someone realises they're diabetic, they change their eating habits, have sweetner instead of sugar, take a packed lunch to work instead of eating stuff out of vending machines. Someone realises they're intolerant of wheat or lactose, they minimise their intake of it. Someone realises they smoke too much, they try to quit or at least cut down. It involves big lifestyle changes but they know it will make their lives better or at the very least stop them getting/feeling worse. Any sensible person knows they don't need a whole 14inch pizza and a portion of chips for dinner for one. That you don't reward sticking to a diet for a day with a cream cake the next day. That a Bic Mac has calories even if you eat it while walking and order a diet coke with your meal.