Just a quick link, check out:
As the title suggests, it has a whole lot of pictures of what 200 calories looks like.
When you are doing the 5:2 diet, it helps to be able to quickly picture how much you can have.
As a girl, on your fast days you should be aiming for 500 calories, so 2.5 of any of these pictures over the entire day. As a boy, you get 600 calories, so 3 whole pictures worth.
Choose badly and you get one lump of butter, half a burger from MacDonalds and a blob of peanut butter.
Or you could have a huge stir fry of veggies.