Effects of Vegetarian Diet on Psoriasis Symptoms

In Healing Psoriasis: The Natural Alternative, Dr. John Pagano highlights the importance of a high intake of vegetables in the fight against psoriasis. Also several other books recommend diets emphasizing plant-based foods to people with psoriasis. So, what's the deal? Let's find out!

Studies Associate a High Vegetable Intake with a Decreased Incidence of Psoriasis

An observational study published in the Journal of Translational Medicine in 2015 found an inverse association between the incidence of psoriasis and fruit intake, and a positive association between the incidence of psoriasis and consumption of red and processed meat. What's more, the Psoriasis Area and Severity Index (PASI) scores and C-reactive protein (CRP) levels, which were used to assess the severity of psoriasis in this study, were negatively correlated with the consumption of fruit and vegetables (and a few other food groups) and positively correlated with the consumption of red and processed meats. Similarly, an observational study conducted in Norway and published in the British Medical Journal documented a decrease in psoriasis symptoms with an increase in fruit and vegetable consumption in men (but interestingly not in women). In yet another observational study, published in the British Journal of Dermatology, researchers found a statistically significant inverse association between psoriasis risk and the intake of carrots, tomatoes and fresh fruit. They also observed an association between psoriasis risk and the intake of green vegetables, but only with borderline statistical significance.

But correlation does not necessarily imply causation. Therefore, in addition to the observational studies described above, we should look at some interventional studies. In one such study, a vegetarian diet, preceded by a 2-week fast, resulted in significant symptom relief in some psoriasis patients. This study also looked at the impact of a vegetarian diet on other chronic inflammatory disorders, including atopic eczema, but the positive effects were only observed in psoriasis patients.

Possible Mechanisms Behind the Benefits of Vegetarian Diets

Psoriasis is considered an inflammatory disorder that is characterized by high serum levels of various pro-inflammatory cytokines. It has been proposed that the inflammatory reaction that triggers psoriasis flare-ups results from an interaction between innate immunity (mediated by antigen-presenting cells and natural killer T lymphocytes) and acquired immunity (mediated by T lymphocytes). Vegetables and fruits are rich in antioxidants, which have anti-inflammatory properties and which may therefore help fight the inflammatory reaction that triggers psoriasis symptoms. In addition, vegetarian and vegan diets are typically low in arachidonic acid, an omega-6 fatty acid that is abundant in meat, especially fatty red meat. When oxidized by certain enzymes, arachidonic acid is transformed into a variety of products, some of which mediate or modulate inflammatory reactions.

Why a Pescetarian Diet Might Be Better Than a Strict Vegetarian Diet

After reading about the potential anti-psoriasis effects of a high vegetable intake above, you might be tempted to embrace a strict vegetarian diet. However, going pescetarian, rather than vegetarian, might make more sense (a pescetarian diet includes fish and other seafood, but not the flesh of land-based animals). In a study published in the European Journal of Clinical Nutrition, patients with psoriasis were asked to eat 170 grams of white fish daily for a four-week run-in period, after which the subjects were randomly assigned to one of two groups: the first group continued with the white fish diet while the second group received 170 grams of oily fish daily for six weeks. An improvement was observed in those who followed the oily fish diet (the white fish diet had no statistically significant effect on psoriasis severity). The authors concluded that regular consumption of oily fish that are rich in anti-inflammatory omega-3 fatty acids – such as mackerel, sardines, salmon, pilchard, kipper or herrings – might be useful in the treatment of psoriasis.

References:
1. L. Barrea (2015). Nutrition and psoriasis: is there any association between the severity of the disease and adherence to the Mediterranean diet? Journal of Translational Medicine, Jan 27, 13:18.
2. G. Kavli et el (1983). Psoriasis: familial predisposition and environmental factors. British Medical Journal, 291(6501): 999-1000.
3. L. Naldi et al (1997). Dietary factors and the risk of psoriasis. Results of an Italian case-control study. British Journal of Dermatology, 134(1), 101-106.
4. H. Lithell et al (1983). A fasting and vegetarian diet treatment trial on chronic inflammatory disorders. Acta Derm Venereol, 63, 397-403.
5. M. Wolters (2005). Diet and psoriasis: experimental data and clinical evidence. British Journal of Dermatology, 153(4):706-14.
6. P. Collier et al (1993). Effect of regular consumption of oily fish compared with white fish on chronic plaque psoriasis. European Journal of Clinical Nutrition, 47(4), 251-4.

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