In irritable bowel syndrome (IBS), patients experience gastrointestinal symptoms without any visible damage to the digestive tract.

Many patients with IBS believe that specific foods, like gluten or wheat, trigger their symptoms, prompting them to exclude these foods from their diets without consulting a dietitian or their doctor.

Unsurprisingly, about a third of IBS patients develop disordered eating habits and perceptions about food that may cause symptoms in and of themselves, such as orthorexia, or an unhealthy preoccupation with healthy eating.

This may cause a "nocebo effect," where patients experience symptoms due to their beliefs and expectations about a substance they assume is causing their issues but is actually inert – a "nocebo."