How do you tell if your dog is overweight? Some believe that if you can feel ribs then the dog isn't fat. This can be misleadingâ€¦internal fat can accumulate and push the ribs outward, so that they can be easily felt. Some types of mastiffs carry extra weight very well and donâ€™t look sloppy. Look at your dog from above. Some indentation behind the rib cage, indicates that your pet is at a desirable weight. You may hear owners referring to their fat dog as having "lots of substance". Substance and fat are NOT the same things. Just like in humans, extra weight = extra health risks. Heart problems, arthritis/joint problems, diabetes, high blood pressure, higher risk of heat stroke, respiratory difficulties and shorter lifespans. There could be a medical reasonâ€™s for your dogâ€™s extra weight such as hypothyroidism or cushing's disease.