Psoriasis is a T cell mediated inflammatory skin disease characterized by hyperproliferation and reduced differentiation of epidermal keratinocytes. In severe cases, the disease can result in an insufficient nutritional status which may even be promoted by nutrient-drug interactions. Both the general diet and single food components have been suggested to play a role in etiology and pathogenesis of psoriasis. Fasting periods, vegetarian diets, and diets rich in omega-3 polyunsaturated fatty acids from fish oil have all been associated with improvement in some studies. The most likely explanation is the reduced amounts of arachidonic acid and the increased eicosapentaenoic acid intake resulting in a modulated eicosanoid profile. However, only one of four controlled studies showed a benefit of omega-3 fatty acids compared to placebo. Some psoriasis patients are gluten-sensitive and may benefit from a gluten free diet. The active form of vitamin D exhibits anti-proliferative and immunoregulatory effects and has been shown to be useful in the treatment of psoriasis.