What is the science behind early losses?

[Flossyfloof]

I know lots of people lose several lbs in the first couple of weeks. I don't think I will be one of them
It cannot be fat thought can it? For 5lbs which seems quite normal, you would be expending 17,500 more calories than you consumed; is that possible?
If not, how does it work?

It's the sudden change in diet, you lose a load of fluid as well.

Though 5lb isn't a huge first week loss, I mean it's perfectly decent, but I've seen people lose 10 in their first week and I know I can (just over target) lose 3 or 4 if I stick to it properly.

Bloody hell, 5lbs would be a miracle for me!

Many moons ago in A level biology I was taught it was to do with losing glycogen stores in the liver, apparently that can be several kgs worth. I have no idea if it is true or not though!

"Bloody hell, 5lbs would be a miracle for me!"

Not for a first week if you're following it 100% and are totally overhauling what you eat.