I fed my old chubby dog Science Diet Light until she passed at 17 years a couple months ago. Kept her within a pound or two of her ideal weight.
I also have seen good success with rx diet Science Diet metabolic mobility - get some joint supplements in there since most overweight dogs have some arthritis issues as well. I had a Weimaraner patient lose 25# in a few months easily just by switching the food.
Purina Overweight Management is another one, is also rx only.
But yes, measure out the food, make sure not stealing the others, and feed less of the one you had her on.
Usually I tell clients to decrease overall amount of food 20% to start, cut treats out or in half, and feed veggies instead of table scraps. If that isn't working, then go to diet otc food, and if that isn't working then rx diets.
9/10 they are just feeding them too much, but their metabolisms differ just as ours.
Hypothyroidism can play a role sometimes in middle-age/older pets but usually they are just fat. But if weight gain was sudden then have a T4 checked.
