Start with condition, not with brands
The most valuable diet conversation begins with the dog, not the bag. Ask the vet to score your dog's body condition and tell you the target, because every feeding decision hangs off whether this dog needs to gain, lose, or hold steady. Then ask what that means in grams or measured cups of the food you actually feed — packet guides are written for an average dog who may be nothing like yours, and the difference between a level and a heaped scoop is a common hidden cause of slow weight gain.
Bring the exact food with you, or photograph the label: the vet can judge a diet far better from its composition and energy density than from a product name remembered approximately.
Life stage, activity, and change points
Ask whether the food still fits your dog's stage of life. A neutered adult needs fewer calories than the entire youngster he was at a year old; a senior dog may need more digestible protein to maintain muscle even as total calories fall; a dog whose walks have shortened after an injury can gain weight on an unchanged ration within weeks. Good questions include when to transition foods, how to make the change gradually over several days to protect digestion, and what stool, coat, and energy changes would tell you the new diet suits him.
If your dog has a sensitive stomach, itchy skin, recurring ear trouble, or joint stiffness, ask directly whether diet could be contributing and whether a structured trial — one change at a time, held long enough to judge — is worth doing.
Treats, extras, and the household problem
Ask how treats should be accounted for. For many dogs the meals are right and the extras are the diet: training treats, chews, the corner of several sandwiches, and food from more than one family member. A useful rule to confirm with your vet is keeping treats to a small, defined share of the day's food, taken out of the ration rather than added on top. Dental chews and long-lasting chews carry real calories and should be counted, not treated as fresh air.
If several people feed the dog, ask the vet to state the total daily amount plainly enough that it can be written on the fridge — one measured pot for the day solves most multi-feeder confusion.
Turning answers into a record
It is also worth asking what not to feed. Cooked bones can splinter, fatty scraps can trigger painful digestive upsets, and some everyday human foods — onions, grapes and raisins, and sweeteners found in sugar-free products — are dangerous to dogs even in small amounts. If your household shares food with the dog as a matter of affection, ask the vet for safe swaps that keep the ritual without the risk. Finally, ask how you will know the diet is working: expected stool quality, coat condition, energy, and weight trend give you a scorecard to judge by at the recheck rather than by the dog's enthusiasm alone, which every food passes.
Leave with numbers, not impressions: target weight, daily amount of the named food, the treat allowance, and when to reweigh. Diet changes should be judged at a recheck in a few weeks, not by eye at home. Recording the agreed ration, the target weight, and the recheck date in KinsLe's Pet Passport means that six months later you can see exactly what was decided and whether it worked.