I donated more than 20 years ago and have gained weight and lost hair. And that's my story and I'm sticking to it!

OK, the reality is that after more than 15 years of monitoring living donation issues I've not heard of a relationship between weight gain and kidney donation. While medical research has shown things like higher levels of proteinuria and blood pressure associated with donation, weight gain has not one of the associated factors.
As Fr. Pat suggests, try the Facebook group to see if you can get more information, although it may be anecdotal.
Let us know if there's anything else we can to do help.