What would cause a hamster to be fat one day and skinny the next?

Someone switched hamsters overnight.

Bulimia. Check for a large puddle of vomit hidden in the back of the cage.

Are there a bunch of hamster babies running around?

Dehydration.

Is it just in the front? They do store food in their cheeks.

Have you been keeping up with his Botox injections?

He might have emptied his food pockets, causing him to look drastically smaller than the last time you saw him.

Maybe it took a MONUMENTAL crap?

A workout with Chuck.

Maybe he ran a marathon on his exercise wheel.

A very large bowel movement.

Could it have had babies and eaten them?

What if it was suffering from edema?

Is he wearing all black clothing today? Black is very slimming.

Poor @buckyboy28, we’re not being very much help, are we? I bet you didn’t realize your question would be feeding a straight line to a bunch of comedians.

Good one, @elijahsuicide.

Not that there weren’t some serious answers here, but still.

You might be able to save this by furnishing a few pertinent details. For instance, is the hamster male or female, young or old, alone in the cage, behaving unusually in any other way, getting any different food, etc.? There are folks around here who do know animals and might be able to help.

Speaking of edema, maybe if it is a she, it was PMS.

A REALLY bad case of kidney stones?

My maternal grandmother’s sweet and sour cabbage soup would have the opposite effect. Skinny today, gasbag tomorrow

We’re doing a fine example of following the guidelines everyone.
I’m amazed that it took four responses before someone tried to help.

Rabbits might have babies overnight and then eat them before anyone is the wiser. If your hamster has a boy hamsters in the cage with it or is new from the pet store then that might be the sad truth. I don’t know if that happens with hamsters but I hope it didn’t.

@mrswho You may be on to something there. Hamsters, bunnies, and other critters will eat their young, especially first-time mothers. I had a doe bunny recently that ate three litters in a row until I ate her.

decomposition.

I’ve bred hamsters, they very rarely will eat more than one before you figure it out. And it’s usually the smallest. This was probably not the case.

Time dilation at work. Did you sleep near a black hole? Seriously, I agree with @bob_: dehydration.

@asmonet…omg, you’ve bred hamsters?!?

HAMSTER WHORE!!! Ewwwwwwwwwwwwwwwwwwwwwwww!!!

You’re jealous. :)

maybe