Why do I weigh the least in the morning?

I weighed myself last night before going to bed and was 180 lbs. Woke up this morning, weighed again and was 175 lbs. This has always seemed to hold true, but I thought about it for the first time today. Nothing had changed. I was wearing the same clothes, and did not move the scale. I even repeated the measurements to be sure, both at night and the morning.

The usual explanation given is that you haven’t eaten yet, therefore, the stomach is empty and you weigh less. Seems ok until you consider that mass must be conserved. So, since I didn’t… how do I say this… “Drop the kids off at the pool” where did those five pounds go?

Through total water loss overnight, including vapour from your lungs. See here.

Well, that was quick. Thanks.