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 value' 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?

[Pinotage]

I'd guess the water content evaporates during cooking.

[darth vader]

boiled or baked?

if baked then it's down to water loss

[xyzzyplugh]

Peeling? :-)

[Cathy]

I don't know about why a potato weight less, but if you're doing the weight watchers thing, I wouldn't worry overly much about it. Just use your common sense. If it's a medium sized baked potato it will be 2 1/2 points, if it's large 4 points. The weights they give you are more of a guide when it comes to something like this. I think the idea of it is to get you into good eating habits. Anyway, this is how I've been doing it, and I've lost 2 1/2 stone. Good Luck, I hope it works for you.