Irritable bowel syndrome (IBS) affects about 10 to 15 percent of adults in the United States, according to estimates by the American College of Gastroenterology. Irritable bowel syndrome is a group of intestinal symptoms that occur together. Symptoms can include: Abdominal cramps, bloating, gas, constipation, etc. Although different triggers affect different people, a variety of factors can trigger them. symptoms, including alcohol.