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Your brother probably has Gluten sentitive enteropathy
or Celiac disease
. Swelling of body is a symptom of this disease because of less absorption of protein from the intestine. He needs to stay away from wheat, barley, rye, oats which contain gluten and also take less salt in diet. Try to avoid milk products if he is allergic to them as well. Since he is having pain, is there any redness and increased warmth of the skin on that area, if yes it could be inflammation of the tissue called cellulitis
which needs urgent medical attention. Doctor will need to prescribe diuretic
if edema if not relieved but usually relief is obtained following gluten free
diet. He can eat plenty of fresh fruits and vegetables, pulses, chicken, lean meat, eggs.