The question of what to eat permeates our daily lives. It rings especially true when you’re living with a chronic disease like psoriasis. When April Armstrong, M.D., MPH, sees patients, many ask what factors they can control when it comes to managing their disease – particularly their diet.
“One of the most common things I hear is, ‘I’m trying this diet, but it’s not really working. What other diets do I try?’” she says.
To get at the heart of this question, Armstrong led an effort among fellow members of the National Psoriasis Foundation’s medical board to comb through the scientific literature on the relationship between food and psoriasis. What resulted is a paper on diet recommendations for people with psoriatic disease published in JAMA Dermatology in August 2018.
The review draws from data on more than 4,500 people living with psoriasis across 55 studies, providing the most comprehensive picture yet for what scientific evidence reveals about which foods and supplements most significantly affect disease severity.
The authors are quick to point out, however, that medical treatments still lead the way in tackling psoriasis, and evidence has shown that the primary role of diet is to help mitigate disease symptoms in some patients.
“There is what’s called a reporting bias – people who try something that works for them are going to speak more loudly than if it didn’t.” Armstrong says. “That gives you a perception that it works for lots of people.”
Calorie counting can help … for some
The paper’s strongest recommendation is to reduce caloric intake if you are overweight or obese.
The link between weight and symptom severity among psoriasis patients is well established. In part because of body fat’s pro-inflammatory role, overweight or obese individuals face a host of issues – ranging from more severe symptoms to reduced treatment response – when trying to manage their disease.
The review recommends using weight loss to help mitigate these factors through what is known as a hypocaloric diet. In this case, “hypocaloric” refers to weight loss driven solely by consuming a smaller number of calories, rather than by exercise, surgery or changing nutrient portions, such as carbohydrates.
“Weight loss will undoubtedly help your heart, but we certainly know that it can help your psoriasis too,” says Mark Lebwohl, M.D., a member of NPF’s medical board and co-author on the paper.
Of all the non-medical interventions overweight or obese people can receive, researchers gave evidence for hypocaloric diets their highest grade. Data on how weight loss affects people with a healthy weight, though, remains lacking.
Not quite making the grade
Gluten-free diets, originally intended for people with celiac disease or gluten sensitivity, have skyrocketed in popularity in recent years. Armstrong and Lebwohl agree that it isn’t uncommon for patients in the clinics to inquire about eliminating gluten.
While the authors strongly recommend gluten-free diets for people who face both celiac disease and psoriasis, they do not recommend the diet for anyone who has not tested positive for markers for celiac or gluten sensitivity.
Based on the lack of quality evidence for other supplements, such as selenium, fish oil and vitamin B12, the paper does not currently recommend them for psoriasis patients.
While topical vitamin D has been established as an effective treatment for psoriasis, there is little high-quality evidence to support the role of orally taking vitamin D to improve psoriasis, and the authors don’t recommend using it for prevention or treatment in adults with normal levels of vitamin D. Among patients with psoriatic arthritis, the paper suggests patients try one month of supplementation in addition to regular treatment.
Further evidence needed
In addition to offering diet recommendations, the authors highlighted some directions for future research. A hypocaloric diet in one study isn’t always the same as a hypocaloric diet in another, says Adam Ford, co-author on the paper and M.D. candidate. Diets mentioned in the study varied from 1,400 calories a day to a meager 800 calories.
“There’s a lot of questions that still need to be answered, besides just getting to the bottom of these different supplements,” he says. “Even then, we still have a lot of work understanding the mechanisms by which improvements in psoriasis happens."
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