I've heard that food that contains wheat can produce soft stools in dogs... anybody else heard that? This Halla Foder contains no wheat.

I'm just thinking about trying it on my 2 year old bitch... she recently had puppies about 4 months ago. I've been trying to get her weight back on by feeding her little more than usual and she's been having soft stools... no scratching what so ever and her coat is coming back in. So I'm wondering if I should try brand or not or just stick with the old one?