As an example, let's say Max is a Chihuahua whose ideal weight should be about 6lbs. unfortunately, due to the extra snacking, Max weighs 7.2 lbs. For a dog of his stature, he would be considered obese. This puts extra pressure, not only on his spine, knees and other joints, but is also dangerous for his heart, liver, and kidneys.
The easiest way to decide how big is too big is the "bone test." From Max’s shoulders to his hips, feel both sides simultaneously. Your goal is to be able to appreciate each rib with a thin layer of fat over it. The same goes for the shoulders, hips and near the tail. If you can see the bones, the dog is underweight. From the side, you should see an obvious dip where the waist is. From the top, you should be able to see a curve in from the ribs to the waist and then back out toward the hips. If you can't see or feel the bones, chances are your dog is on his or her way to becoming very unhealthy.
The best way you can help your dog is regular veterinary care. Before making any changes to your dog's diet or starting them on an exercise program, as with humans, always check in with the doctor first. Exercise is key. You have to find a way to keep it fun and have a variety so that you and your dog don't get bored. Swimming is good because it will not put stress on any joints. Walking on different types of terrain, as done in a hike, is good for them as well. Fetch is always a good standby. If your dog is obese, they are more likely to have trouble breathing or to become overheated more quickly. It's important to keep an eye on them and to make sure they drink enough water.
Changing their food to a high-quality food without fillers or even to a diet food will help. Stick to the recommended amount based upon your dog's weight as noted on the bag. Break that amount into smaller meals. It may seem like more work initially, but you and your dog will both become used to the routine. If you have more than one dog, you should feed them separately if one is overweight so that the dog on the diet doesn't get overfed. Table scraps are always a no-no. Resist the cute puppy dog eyes!