I have a friend who is repulsed by food he only eats bread…

He seems to have Obsessive-compulsive disorder (OCD) that is an anxiety disorder characterized by unreasonable thoughts and fears (obsessions) that lead you to do repetitive behaviors (compulsions). With obsessive-compulsive disorder, you may realize that your obsessions aren't reasonable, and you may try to ignore them or stop them. But that only increases your distress and anxiety. Ultimately, you feel driven to perform compulsive acts in an effort to ease your stressful feelings.
Obsessive-compulsive disorder often centers around themes, such as a fear of getting contaminated by germs. To ease your contamination fears, you may compulsively wash your hands until they're sore and chapped. Despite your efforts, thoughts of obsessive-compulsive behavior keep coming back. This leads to more ritualistic behavior — and a vicious cycle that's characteristic of obsessive-compulsive disorder.
The cause of obsessive-compulsive disorder isn't fully understood. Main theories include:
Biology. OCD may be a result of changes in your body's own natural chemistry or brain functions. OCD also may have a genetic component, but specific genes have yet to be identified.
Environment. OCD may stem from behavior-related habits that you learned over time.
Insufficient serotonin. An insufficient level of serotonin, one of your brain's chemical messengers, may contribute to obsessive-compulsive disorder. In addition, people with obsessive-compulsive disorder who take medications that improve the action of serotonin often have fewer OCD symptoms.
Obsessive-compulsive disorder treatment can be difficult, and treatment may not result in a cure. You may need treatment for the rest of your life. However, OCD treatment can help you bring symptoms under control so that they don't rule your daily life.
Main obsessive-compulsive disorder treatments
The two main treatments for obsessive-compulsive disorder are:
Psychotherapy
Medications
Which option is best for you depends on your personal situation and preferences. Often, treatment is most effective with a combination of medications and psychotherapy.
Sometimes, medications and psychotherapy aren't effective enough in controlling your OCD symptoms. In rare cases, other treatment options may include:
Psychiatric hospitalization
Residential treatment
Electroconvulsive therapy (ECT)
Transcranial magnetic stimulation
Deep brain stimulation