Fluid moves constantly from inside your arteries and veins to the spaces between tissue cells and back again. How hydrated you are, what you’ve eaten, your activity level and where you are in your menstrual cycle (along with a host of medical issues) can all affect this flow. Around to your period, or when you’ve eaten lots of salt, you may retain extra water in your tissues, which can cause bloating—yup, even 5 pounds’ worth. Pounds easily gained are easily lost, too: If you drop a couple lbs in a day or two, it’s just water weight.

READ MORE: What Is Water Weight?