What are the chief causes of unexplained weight loss?

When considering the cause of unexplained weight loss, it’s important to determine whether the person still has a good appetite or not, and reviewing the number of calories the person is actually eating. Appetite loss leading to decreased caloric intake is the usual problem. Causes of persistent loss of appetite include medication side effects, stomach, liver, and bowel disorders; depression; chronic pain; diabetes and cancer. Weight loss despite consuming plenty of calories can happen in people with an overactive thyroid gland (hyperthyroidism).