Yup- 1 syn per 20 calories is a good guide for non-sw food but this doesn't take into account free food. So use it for sweets, biscuits and crisps, but it goes out of the window when counting actual food- eggs, meat, veg, fruit, readymeals, etc. e.g. an egg is about 70 cals but free on SW
It may be helpful for you to get a food directory from the on-line bookshop, eBay or a friend if you know anyone who goes to class. This way you can take the guesswork and estimation out of it
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