Getting off Atkins, help!?

So, I was on Atkins for about 3 months and I have finally come to the realization that this is not a healthy and effective way to lose weight and KEEP it off. I was not excercising when I was on it. I decided about a week ago to discontinue that weight loss program and start getting active! I have started working out 4-5 days a week for about an hour a day. I joined a gym and signed up for a personal trainer today but I'm EXTREMELY concerned of packing weight back on after changing my eating habits so drastically. Does anyone know a safe, effective way to change my diet without gaining back a lot of weight. I know I will gain back some, I just don't want to gain tons. Any help will be appreciated. Thanks!!