To follow the book, only buy products where the sugar is not fructose, such as natural yoghurt, and get your minimal sugar a day eating fresh fruit. Labels can try to confuse you, for example by listing sugar three different ways. If they give you g per 100g, that is obviously a percentage, but g per 200g would not be, for example.
Personally, I go by amount, in the sense that I would not eat jam on my toast, but I'd eat a small amount of chilli jam on my steak from time to time. The % is the same, but I eat so little chilli jam that I figure it's not enough sugar to worry about SO LONG as I do even that rarely ( I usually use this rule when trying to work out what to eat in a restaurant, not to excuse eating sugar at home ). If a product has 50% sugar and you eat a tea spoon, that's better than a soft drink being 30% sugar ( or even 10% ) and you drinking a litre.
