Polymyositis (pol-e-mi-o-SI-tis) is a rare muscle disease that usually affects adults. A few studies that looked at small numbers of people with polymyositis over a number of years found that a gluten-free diet was linked to symptom reduction.
Without stronger evidence, though, having polymyositis doesn't mean you need to eliminate gluten from your diet — unless you also have celiac disease, which may be more common in people with polymyositis than in the general population.
In celiac disease, an abnormal immune system reaction keeps your small intestine from absorbing gluten, which is a protein in wheat, rye and barley. Eating these grains invariably causes digestive distress, as does eating processed foods containing gluten. A gluten-free diet is the basic requirement for living with celiac disease.
If you have polymyositis and you develop persistent iron deficiency anemia with weight loss and frequent bouts of diarrhea, your doctor may recommend testing for celiac disease.