So I was freaking out the other day about a really miniscule gain (3lbs isn't much, but I'm trying to win a Biggest Loser competition that ends on the 13th; I'm apparently in the running for cash prizes, so every pound counts at this point if I want some extra $$!), and I thought about something -- I just finished taking an antibiotic for a little bacterial infection... could that be why my body is having a mini freakout?

I gained 8 pounds in as many days when I was on an antibiotic last fall despite being completely on plan. And yes, antibiotics can make you retain water. Tooke me like a week to lose that water weight too.

It's more likely to be the infection than the antibiotic (infection = immune response = swelling and water retention). Some antibiotics might mess with the bacteria in your intestines, which could affect fluid balance as well.

Either way, it's likely water weight.

No, it was the antibiotic that made me gain or the effects of it. I went up exactly a pound each day I was on it and hadn't gained any with the urinary tract infection I had which I didn't even know I had but was found in a routine test. Did some research on this antibiotic and a common side effect is weight gain. Temporary and water yes, but weight nonetheless.

Yeup.

This is one of the many reasons I don't take antibiotics unless it's absolutely necessary. In Laymen's terms - Antibiotics destroy ALL your gut flora. Not just the critters we don't want running around. ALL of the critters. Some of those bugs do a good job of cleaning up your insides and killing things like yeast that can cause inflamation and water retention. You need your gut flora for a billion reasons.

You need to recolinize yourself ASAP. I make Kefir at home, but if you can't stomach that you can buy it commercially or eat yogurt with live cultures.