Coeliac disease (also called gluten enteropathy) is a disorder of the small intestine characterised by sensitivity to gluten. In people with coeliac disease, eating gluten causes inflammation in and damage to the lining of the small intestine, resulting in diarrhoea, malabsorption, fat in the stool, and nutritional and vitamin deficiencies.

A gluten-free diet is the primary treatment for coeliac disease. Strict avoidance of wheat, barley, and rye (the three most abundant sources of gluten) usually improves gastrointestinal symptoms within a few weeks, although in some cases improvement may take many months. People with coeliac disease must remove all gluten-containing foods from their diets in order to relieve symptoms. Following a gluten-free diet has been shown to reduce the incidence of cancer, low bone mineral density, and infertility in persons with coeliac disease.

People with dermatitis herpetiformis may benefit from following a gluten-free diet. The cause of dermatitis herpetiformis is mainly an allergic-type reaction. Gluten-sensitivity enteropathy is found in 75 to 90% of people with dermatitis herpetiformis. Unlike coeliac disease, however, gastrointestinal symptoms are mild or absent. Strict adherence to a lifelong gluten-free diet can eliminate dermatitis herpetiformis symptoms and intestinal abnormalities, as well as reduce or eliminate the need for medication in most people. However, an average of 8 to 12 months of dietary restriction may be necessary before symptoms resolve. Not all people with dermatitis herpetiformis improve on a gluten-free diet. Preliminary studies indicate sensitivity to other dietary proteins may be involved.

Anecdotal evidence suggests that people with psoriasis may improve on a hypo-allergenic diet. Three trials have reported that eliminating gluten (as found in wheat, rye, and barley) improved psoriasis for some people. A doctor can help people with psoriasis determine whether gluten or other foods are contributing to their skin condition.

Preliminary evidence suggests that a gluten-free diet may help improve symptoms of rheumatoid arthritis. In one trial, 14 weeks of a gluten-free (no wheat, rye or barley), pure vegetarian diet, gradually changed to a lactovegetarian diet (permitting dairy), led to significant improvement in rheumatoid arthritis as evidenced by associated symptoms as well as by objective laboratory measures of disease.

HIV enteropathy, a complication of AIDS that is characterised by weight loss and chronic diarrhoea, may respond to a gluten-free diet. In a preliminary trial, men with HIV enteropathy experienced a reduction in the number of episodes of diarrhoea as well as significant weight gain while following a gluten-free diet.

For many years, researchers have been speculating that certain dietary proteins, including gluten, may contribute to the symptoms of schizophrenia. People with schizophrenia are more likely to have immune-system reactions to gluten than the general population, according to some studies. While clinical research findings have been inconsistent, some, but not all, people with schizophrenia may benefit from a gluten-free (and dairy-free) diet.