Why do I weigh less in the morning than I do at night

I’m currently trying to lose weight. Actually, my wife and I have a bet going on who can lose weight the fastest. My goal is 30 pounds, and hers is 20.

I’ve been weighing myself everyday. I’ve noticed that, if I weigh myself at night, right before I go to bed, and weigh myself again first thing in the morning (usually after my morning piss), I can weigh up to 3 to 4 pounds less than I did the previous night. Typically, by the end of the day, it’s back up to were it was before, sometimes slightly less.

I doubt my piss weighs that much. How do I lose that much weight at night? Where does it go? Into my mattress? I’ve heard the term “water weight” bandied about. Is that what it is?

You’re constantly losing water from your skin surface due to evaporation. Since you’re not taking anything in overnight, you see a net water loss. Have a drink in the morning, and the tide comes back in.

It might. Between taking a leak, and the evaporation that Ethilrist speaks of, you could easily be loosing 3-4 pounds. That’s only about a half-gallon of liquid.

Evaporation! Of course!

I’m relieved. I thought I must have been sweating buckets in bed.

Yep. When you go backpacking, if you use a down sleeping bag you’re supposed to hang it up for a while in the morning so it has a chance to dry out from all the water you gave off during the night.

You will also be losing some weight during sleep as some of your fat or other tissues is converted to carbon dioxide through respiration and exhaled in that form. However, since you are resting, the amount of weight loss this way will be relatively slight, and I would agree that the majority of the weight loss during the night will be due to urine/perspiration.

We also exhale a fair amount of water vapor as we breathe. All that fog that appears when you breathe on a cold window? That much comes out with each breath. It adds up over 8 hours.

You also lose water vapor each time you exhale.

Not to mention that scales might be more sensitive to the slight loss, as opposed to the slight gain, showing 2-3 lbs as something more.