Obesity: Obesity is just as dangerous for Cavalier King Charles Spaniels (dogs) as it is for humans. Fat Cavalier King Charles Spaniels (dogs) are a higher risk in surgery, more prone to injury, as well as to metabolic disorders such as diabetes, and have more stress on their heart, lungs, liver, kidneys, stomach, intestines, and joints. Consult your vet about a reasonable diet for your Cavalier King Charles Spaniel (dog).