Clinical Review

The Impact of Diet on Psoriasis

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Ketogenic Diet

As obesity and weight gain are factors associated with psoriasis, some patients turn to diets that restrict calories with the goal of losing weight to improve their symptoms. One 2015 case report studied a patient who restored her response to systemic treatment of psoriasis following an intensive 4-week, calorie-restricted ketogenic diet.11 The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet. Animal studies have shown the diet to have anti-inflammatory effects, including lowering levels of proinflammatory cytokines and reduced fever.12 In the 2015 case report, the rapid and consistent weight loss experienced by the patient because of the ketogenic diet was thought to be the cause of the restoration of treatment effectiveness,11 which is interesting, since the role of the ketogenic diet was not to supplement any deficiencies but to move the patient to a physiologic state that was once again receptive to treatment. This finding suggests that a variety of diets could improve psoriasis symptoms, so long as they do not cause inflammation or reduce overall body mass. One study of patients on a calorie-restricted diet over 8 weeks did see a trend of patients on the diet showing improvement in both their PASI scores and Dermatology Life Quality Index, though the improvement was not statistically significant.13 To determine if the ketogenic diet has a significant association with psoriasis improvement, controlled, large-population studies should be performed in the future with age, sex, and weight-matched controls, which may be difficult to do. Further studies looking at the association between weight loss and psoriasis also could be another direction.

Vegetarian Diet

Both vegetarian and vegan diets have been evaluated for their efficacy in relieving symptoms of chronic inflammatory disorders. Although the 2 diets are similar in avoiding consumption of meat, fish, and poultry, vegan diets often have additional food restrictions, including avoiding eggs, honey, and dairy products. One study noted the impact of these diets on patients with a variety of skin conditions following a period of fasting. It was observed that some patients with psoriasis saw an improvement in their symptoms during the period when they were eating a vegetarian or vegan diet, which was attributed to a return to normal levels of activity of neutrophils, extrapolated from serum levels of lactoferrin.14 Vegetarian diets have been shown to be associated with higher ratios of anti-inflammatory to proinflammatory adipokines compared to omnivorous diets,15 as well as lower expression levels of proinflammatory genes in the gut microbiota and lower expression levels of IgE.16 Perhaps the anti-inflammatory impacts of the diet affected the symptoms of psoriasis. The benefits of a vegetarian diet also have been attributed to the high amount of potassium consumed,17 which is used in the body to synthesize cortisol, a common treatment for psoriasis. Potassium supplementation has been shown to raise serum cortisol levels in patients.6 Although additional studies are needed to discern the significance of potassium in the vegetarian diet, both hypotheses are reasonable explanations for the observations seen in these studies.

Vitamin D and Other Nutritional Supplements

Because it is not always feasible for patients to alter their diets, many have turned to dietary supplements as an alternative method of treatment and lifestyle change. Two of the more prominently represented nutritional additives in the literature are fish oils and vitamin D.18 Supplemental vitamin D is a prohormone that can be endogenously converted to its active 1,25-dihydroxyvitamin D.19 Vitamin D plays important roles in the regulation of calcium and magnesium in the bones as well as the maturation and differentiation of keratinocytes in the skin.16 Topical vitamin D analogues are standard treatments for psoriasis, as they are used to modulate the immune system to great effect.20 Some patients with psoriasis present with vitamin D insufficiency,21 and it stands to reason that oral supplementation may be a treatment option. There have been multiple studies assessing the efficacy of oral vitamin D for the treatment of psoriasis; however, in the only randomized and placebo-controlled trial, there was only a slight nonsignificant improvement in the group supplemented with vitamin D.20 Another small, open-label study reported remarkably improved PASI scores in 9 vitamin D–supplemented, dietary calcium–restricted patients.22 The lack of recent, large-sample studies makes it hard to draw notable conclusions from these studies.

The polyunsaturated fatty acids found in fish oils also have been considered as a treatment option for psoriasis.23 Millsop et al20 conducted an analysis of the literature reviewing the efficacy of fish oil in the treatment of psoriasis. Twelve of 15 compiled trials showed an improvement in psoriasis, ranging from slight improvements from baseline levels of the disease to statistically significant decreases in PASI scores (P<.05). It is notable that the amount of fish oil given in these studies varied widely, but the amount given did not necessarily correlate with strength of impact.20 For example, Mayser et al,24 Bittiner et al,25 and Grimminger et al26 each performed prospective, double-blind studies with docosahexaenoic acid and eicosapentaenoic acid (the omega-3 fatty acids found in fish oils), and all 3 studies saw improvements in the omega-3–treated group vs the control group. The doses of the oils, however, ranged from as low as 1.2 and 1.8 g daily of docosahexaenoic acid and eicosapentaenoic acid, respectively, to 4.2 g daily of each fatty acid.24-26

Studies also have shown little to no improvement in the use of fish oil to treat psoriasis. One such study was conducted by Soyland et al27 in 1993 in Norway. Utilizing a prospective, double-blind, placebo-controlled design over 4 months on 145 patients with moderate to severe psoriasis, researchers evaluated the treatment effectiveness via PASI scores; subjective reports from the patients; clinical manifestations; and factors such as cellular infiltration, desquamation, and redness. The results were mixed, with the placebo (corn oil) group having less redness and cellular desquamation and the fish oil group showing less cellular infiltration. In the other categories, there was no significant difference between the 2 groups, and researchers concluded there was no significant benefit to treating psoriasis using fish oil vs corn oil.27 As with many of the other diets, there have been no recent, large-scale studies performed on the effect of fish oil supplementation on psoriasis; however, of the studies we reviewed, none showed fish oil supplementation to have a significant negative impact on psoriasis.


Dietary modifications have a complex multifactorial effect on psoriasis, often dependent on the variations of psoriasis and the lifestyle of the patient, including level of exercise, activities such as smoking and drinking, and genetic susceptibilities to conditions such as obesity. Thus, it is difficult for one diet to have a significant impact on psoriasis symptoms that applies to the majority of individuals. However, it appears that certain foods or nutritional supplements can be modified from all diets for general improvement. Foods with systemic anti-inflammatory effects, such as olive oil and fish oil, seem to be beneficial in treating psoriasis. As an extension, a gluten-free diet may help psoriasis patients with celiac disease by reducing the inflammatory environment of the body. On the opposite side of the spectrum, proinflammatory foods such as dietary fat and alcohol should be avoided.28

In general, larger and more recent population-based studies are needed to add to the literature on this subject. Nationwide voluntary web-based surveys such as the NutriNet-Santé study in France may be one way to quickly amass large quantities of data ( Identifier NCT03335644). Participants are recruited through multimedia campaigns and return online questionnaires annually for 1 decade. A subset of participants also contributes biologic samples and participates in clinical examinations. This type of data gathering would capture many variables, provide a large sample size, and perhaps shed light on regional differences in diet and lifestyle that could then be targeted with treatments.


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