Why do cooked potatoes weigh less than raw ones?

[Wee Kaz]

I am currently on the weight watchers diet which involves weighing your food so you can calculate the 'points valve' Can someone tell me why when I weighed a raw potato and it was just under 400g although once it was cooked it was just over 300g? Does anyone know why it decreases in weight and should I take it as 300g?

[ravenhair]

Potatoes have lots of water in them (as do most fruit and veg) so during cooking the water is released and normally evaporates. I'm afraid I can't answer your question about whether you should count the raw or cooked weight - maybe you could contact a Weight Watchers advisor or representative?