The short answer is yes, this warrants a doctors
visit. There are several reasons for this I will outline below. The first question I would have is whether the weight loss your dad experienced was intentional. Intentional weight loss is not concerning but unintentional weight loss suggests an underlying chronic disease. So if your dad has lost a few pounds after starting diet and exercise program, then good for him. In your dad's age group, unintentional weight loss and abdominal pain mean that he needs evaluated for a gastrointestinal cancer such as stomach cancer or colon cancer (colon cancer being more common). Other possibilities of entities that cause weight loss include a GI infection with a parasite, or an inflammatory bowel disease. Parasite infections in the United States are not that common and Inflammatory bowel disease usually begins much earlier in life. The first step is for you to schedule an appointment with your dad's primary care physician
so he can be evaluated. His doctor may order imaging such as an x-ray or CT scan of the abdomen, or perhaps a colonoscopy
. If anything is found, then he could be referred to a specialist. Good luck, I hope he feels better.