We are aware of the negative health consequences in humans, so why is it ok for our pets to be overweight? That's correct: it's not.
We don't see overweight animals in the wild, only in captivity (our captivity). A fat cat or dog would be lunch to predators in the wild.
I impart a huge amount of importance to weight loss in obese pets. Pets that are overweight have a much higher incidence of diabetes mellitus, cardio-pulmonary disease, arthritis (at least clinically affected with arthritis), and even skin issues (fat pets can't groom themselves properly).
Based on ideal weight, vets can calculate (or simpler: find a table in a book) a pet's daily energy requirements.
For example, a dog's RESTING ENERGY REQUIREMENTS (RER, the energy expended while the dog is at rest) is calculated in this manner: (30 mutiplied by body weight in kilograms) + 70.
This would equal the RER in kilocalories (kcal) per day.
A few examples: If your dog should lose weight, the RER is multiplied by 0.8-1.
A neutered dog would consume 1.6 times RER.
A working dog should consume 2-5 times RER, depending of course, on the type of work (a dog sitting at a computer desk all day doesn't require that many calories).
Talk to your vet about counting calories for your pet.
Over 50% of the pet population is consider overweight, a large percentage of those obese.