I'm not very keen on diet foods bought from pet stores, or even the perscription ones.
I have Akina on a weight loss diet that myself and her doctor came up with from one of her text books.

Speak with your doctor about this diet first, to see if he/she approves of it for your dogs particular situation.

This meal is ment to be fed in small portions several times through out each day, along with GOOD exercise!

1/4 a pound of meat protein source. (Ex, Chicken, Lamb, Beef, etc) I personally use Wysong canned 100% Rabbit, because that's what I have around, and it's less work for me.
2 cups Carrots
2 Cups Green Beens
1/4 Cup Cottage Cheese
Daily Multi-vitamin
Dicalcium Phosphate.