Thank you for wanting to keep him fit and trim, that is very important!!!
May I suggest you check out www.dogaware.com they have a listing of all the top dog food. Also a lot of good information. I use Innova or Wellness brands. If you feed a top quality food it would lessen the defecating. Sounds like Fit & Trim is going through him pretty fast, if he's going 3-5 times a day. Mine only goes twice, maybe three times if I feed her veggies. Also when you do feed a top grade food, you feed a little less.
I have a mini who gains weight looking at the bag. LOL So this is what I do. She is fed a little less than 1/3 of a cup of kibble twice a day, if she starts looking thinner I up the kibble. The morning feeding I include a Pet Tab (vit), Ester-C, a "squirt" of Grizzly Salmon oil and 1 tablet Vetri-Disc. Since your little man is bigger you of course would give him more kibble. If I am doing errands during the day I feed her less kibble, so this way she can have her stuffed frozen Kong to keep her occupied.
If she does start to gain weight, I split her regular kibble with Purina's OM. This way she gets the top food and a weight mangement food and still getting all of her nutrients. You could do the same with Fit & Trim and a top grade kibble.
Thanks so much for all your suggestions. I never knew that there were so many different quality dog foods around!! I just thought dog food is dog food but I stand corrected. My doxie loves to eat anything!! I have to watch him when we go for a walk because if there's anything that even resembles food he will try to eat it. Sometimes I think he is starving. He always gives me the very very sad eyes even after he has been fed. Thanks again for your help and a healthly new year to you!