DALLAS, Sept. 27 (UPI) — People with chronic diarrhea, constipation or painful bloating may be suffering from celiac disease, a condition that affects millions, a U.S. researcher says.

Dr. Prabhakar Swaroop, a gastroenterologist at the University of Texas Southwestern Medical Center in Dallas, says celiac disease is a digestive disorder affecting people sensitive to gluten, which is found in wheat, rye, barley and oats.

In people with celiac disease — including Elisabeth Hasselbeck of ABC’s “The View,” and political commentator and sports journalist Keith Olbermann — the immune system responds to gluten by attacking the small intestine and wiping out tiny fingerlike protrusions called villi, which help absorb nutrients into the bloodstream.

More than 2 million people in the United States have been diagnosed with celiac disease.

“It is often difficult to diagnose because its symptoms are similar to other digestive diseases and conditions such as Crohn’s, irritable bowel syndrome, ulcerative colitis and intestinal infections,” Swaroop says in a statement. “A gluten-free diet is the only treatment for people with celiac disease. Sticking to the diet is a lifetime requirement because eating any gluten will cause more damage.”