weight gain during TOM

I know this might sound like a stupid question but why do we gain weight week before TOM ( time of month ) ? is it just hormones or our body getting ready?

Your uterus swells before you have your TOM. Remember that your uterus is a muscle. It retains water and other fluids and then releases most of that during That One Miserable week. I avoid salt as much as possible and don't gain during or before TOM. In fact, I just lost 3 pounds this past week alone and I have my TOM. I used to gain at least 3 lbs every month and then a couple of days later it would be gone. Everyone is different. Some women don't gain at all, some gain 1 to 5 pounds. I drink lots of water and stay away from salt which seems to work for me. It doesn't help with cramping and I do still feel a little bloated but its not nearly as bad as it used to be. I also have fibroids so you would think it would cause massive bloat etc. But once I cut out the salt I haven't had any problems.