As it turns out, obesity also affects the lungs.
Not only that your dog will have hard time moving and breathing with all that extra load, research in humans has described actual changes to the lungs themselves.
The problem includes changes in elasticity of the lungs and chest tissues.
There are many ways in which we're hurting our dogs by letting them get obese. This is just another one.
Source article:
How Obesity Affects Your Pet's Lungs