It always worries me to hear about a dog with a distended stomach as this could indicate bloat. Bloat (Gastric Dilatation) may or may not involve stomach torsion (twisted stomach). It may be that your dog's stomach is not twisting. Common symptoms are attempts to vomit (usually unsuccessful) and may continue to try to vomit, dog just doesn't seem like themselves, a hunched up posture, anxiety and restlessness, a distended stomach that is tight like a drum, gums may be dark red in early stages and white or blue in later stages. These are the most common symptoms and the list goes on. If you believe your dog has bloat they should be seen immediately. Simethicone products like gas-x may help while you take him into the vet.
You can read more on bloat here.
Parasites can sometimes cause a distended stomach and lead to a loss of appetite as well though we usually see abnormal stools with parasites. If your dog may have ingested a bone or sharp pointed object, it may have punctured the gastrointestinal tract. You can read about this here:
Cushing disease can cause a bloated stomach as well. You can read about this condition here:
I suggest smaller meals with water provided at meal time, and slowing down his eating with moistened food will also help preven gulping air when the dog eats too fast. Prevent exercise for an hour after eating and drinking The exercise can cause the stomach to twist which of course can be deadly. If he tends to gulp large amounts of water from the pool while exercising, you may need to limit this activity to help prevent bloat.
I would definitely discuss this problem with your vet. He may decide that with the problems you are already seeing, that tacking the stomach in place to prevent the stomach from twisting might be in your dog's best interest.
I hope this information is helpful to you.