Psoriasis is a chronic cutaneous disease associated with immune-mediated inflammation. The disease has a complex etiology, with factors such as genetics, smoking, alcohol use, diet, and stress all believed to be implicated in its appearance and severity. Specific factors, including increased body mass index and weight gain, have been associated with a higher prevalence of psoriasis and are risk factors for the disease. Because psoriasis varies in severity and incidence, patients often can experience a substantial negative impact on their quality of life, with increased incidences of anxiety and depression.1 Because diet is an accessible and controllable variable, many patients choose to alter their diets to help relieve symptoms of the disease. This article aims to review and summarize the existing literature for possible relationships and correlations between diet and psoriasis.
Because diet is a factor contributing to psoriasis, it is a lifestyle change that patients often make. In a 2017 survey of 1206 patients with psoriasis, 86% reported modifying their diets.2 Furthermore, when patients were compared with control individuals of the same sex and of similar age, it was shown that those with psoriasis consumed statistically significant lower amounts of sugar, whole-grain fiber, dairy products, and calcium (P<.001). The survey also found that patient diets included significantly more fruits, vegetables, and legumes (P<.01). Although no single diet was adhered to by patients, 40% did report attempting a specialized diet to improve their psoriasis. The most common diets were gluten free (35.6%), low carbohydrate/high protein (16.6%), and Paleolithic (11.6%). In addition to these diets, the Mediterranean diet and a vegetarian diet were both among those reported to improve psoriatic symptoms. Finally, certain foods stood out as more frequently reported to affect symptoms, particularly fish oil, fruits, vegetables, and water, which were all reported by at least 10% of respondents to positively affect their psoriasis. Reductions in consumption of alcohol, gluten, nightshades, and junk foods were associated with skin improvements in at least 50% of patients.2 These baseline differences in diet informed our search of the literature and showed that dietary changes can serve as an important adjunct to treatment for many patients.
Mediterranean Diet
The Mediterranean diet consists of a high amount of fruits, vegetables, nuts and legumes, cereals, and olive oil, while restricting consumption of red meats, dairy products, and alcohol (besides red wine) at meals.3 Adherence to the diet has been associated with a reduced risk for cardiovascular diseases,4 rheumatoid arthritis, and Crohn disease,3 among others, possibly because the diet contains a high proportion and variety of foods that contain antioxidants and anti-inflammatory compounds, including the monounsaturated fatty acids (MUFAs) in olive oil and the polyphenols in fruits and vegetables. Consumption of both MUFAs and highly anti-inflammatory nutrients has been associated with reduced prevalence of risk factors for chronic inflammatory diseases, and consumption levels of MUFAs in particular have been reported to be a predictive factor in psoriasis severity.3
Recent studies have tried to quantify an association between consumption of the Mediterranean diet and psoriasis. One cross-sectional study in 2015 evaluated 62 patients with psoriasis for their adherence to the Mediterranean diet and psoriasis severity.4 Utilizing a 14-question evaluation, the study found that patients with a higher severity of psoriasis, as evaluated by a psoriasis area and severity index (PASI) score and C-reactive protein levels, had a lower adherence to the diet. Notably, consumption of extra-virgin olive oil was found to be an independent predictor of PASI score, and consumption of fish was an independent predictor of C-reactive protein levels.4
A second cross-sectional questionnaire study found similar results in a larger population of 3557 patients. The same association between patients with severe psoriasis and low levels of adherence to the Mediterranean diet was reported.3 Although neither study showed a causal relationship between the diet and psoriasis severity, both did report the potential impacts of proinflammatory and anti-inflammatory foods. General foods and nutrients listed by the studies as having anti-inflammatory properties include MUFAs; fish; vitamins A, C, D, and E; and omega-3 fatty acids.3 Because of the large number of confounding factors in dietary studies that rely on questionnaires, it is hard to definitively label the Mediterranean diet as beneficial topsoriasis. However, individual components of the diet may be used as predictors of psoriasis severity, and the diet itself may be used in tandem with other treatments for psoriasis.
Gluten-Free Diet
Celiac disease is an inflammatory enteropathy caused by an immune reaction to the protein gliadin, which is found in foods containing gluten, such as wheat.5 Immune system assault on the intestinal enterocytes leads to the stripping away of villi, negatively affecting nutrient absorption. Multiple studies have reported an association between having psoriasis and having celiac disease as well as the reverse, including a 3-fold increased risk of celiac disease for patients with psoriasis in a 2017 meta-analysis.6 Even if patients with psoriasis did not have celiac disease, studies have found that a notable percentage of patients with psoriasis have elevated antigliadin IgA antibody levels.7 Many hypotheses have been proposed to explain this association. One article suggested that the malabsorption associated with celiac disease predisposes patients to vitamin D deficiency, which is a contributing risk factor for psoriasis.8 Other explanations involve common immune cells involved in the response to both diseases and a shared genetic background between the 2 diseases.8 As a gluten-free diet is standard for patients with celiac disease, it stands to reason that IgA could be used as a serum biomarker for patients who also could see improvements by adopting the diet.
This result could help explain the proportion of respondents to the 2017 survey who experienced improvements to their psoriasis if the gluten-free diet was in fact not triggering the inflammatory effects that a regular diet would, which also may help to explain the mixed results that the gluten-free diet has had as a treatment for psoriasis. One 3-month study of patients who were positive for antigliadin antibodies found that the majority (82%) experienced a decrease in antibody levels and affected skin area after following a gluten-free diet. Only half the patients had been diagnosed with celiac disease prior to the study, lending credibility to the idea that antigliadin antibody could be used as a marker for patients with psoriasis who would benefit from a gluten-free diet.9 Other case studies have reported no improvement of psoriasis following implementation of a gluten-free diet,10 despite the patients having elevated gliadin antibodies or celiac disease. More studies are required to discern the exact nature of the benefits of a gluten-free diet on psoriasis; however, it does serve as a promising option for patients with both psoriasis and celiac disease.