June 25, 2018
Dietary interventions, used in conjunction with standard medical therapies, can help adults with psoriasis or psoriatic arthritis reduce disease severity, according to a literature review from the Medical Board of the National Psoriasis Foundation.
The new board recommendations, written by Adam R. Ford, BS, from the Keck School of Medicine at the University of Southern California in Los Angeles, and colleagues, were published onlineJune 20 in JAMA Dermatology.
The researchers identified 55 relevant observational and interventional dietary studies representing 77,557 participants, including 4534 patients with psoriasis. The quality of the studies was evaluated on the basis of the Newcastle-Ottawa scale for observational studies and the Cochrane Risk of Bias Tool for interventional studies.
Low-Calorie Diet Highly Recommended for Some
The board found strong evidence to recommend a hypocaloric diet, which means one's calorie intake is less than the amount burned, for overweight and obese patients (body mass index, ≥25 kg/m2) with psoriasis.
In these patients, "a hypocaloric diet [800-1400 calories per day] leads to significant improvements in psoriasis severity, dermatology quality of life, and weight loss, compared with patients consuming a regular diet," Ford and colleagues write.
Laura Ferris, MD, PhD, director of clinical trials from the University of Pittsburgh Medical School's dermatology department in Pennsylvania, told Medscape Medical News that an 800-calorie daily diet will seem too hard to sustain for most, but the evidence that reducing calories helps disease severity is important.
"It gives us a solid foundation to tell patients what is uncomfortable to say and what they don't want to hear, which is you need to lose weight, not just because it's good for your health, but because it's actually going to help your psoriasis or psoriatic arthritis," said Ferris, who was not part of the study team.
Gluten-Free Trial Period for Some
Ferris said she often gets questions about what foods can help with psoriasis, followed by "should I go gluten-free?"
Psoriasis is linked to a more than 2-fold increased frequency of celiac disease. Among patients with psoriasis who tested positive for gluten sensitivity, a gluten-free diet led to significant improvements in clinical severity and in skin biopsy findings after 3 months, the authors write.
Therefore, the board recommends (with a weak evidence level) a gluten-free diet trial for 3 months, but only in patients with a positive blood test for gluten sensitivity.
However, they do not recommend universal screening for gluten sensitivity in adults with psoriatic disease because of the high rate of false positives. Good candidates include those with a first-degree relative with celiac disease or patients with active gastrointestinal symptoms.
The board does not recommend oral fish oil supplementation because it was not effective at doses and durations studied. It could not recommend for or against intravenous fish oil because of limited evidence.
They also note that patients should consult with a healthcare provider before taking supplements because many supplements have adverse effects or contraindications.
Recommendations for Those With Psoriatic Arthritis
For patients with psoriatic arthritis, which affects about one third of patients with psoriasis, the reviewers gave a weak recommendation for adding vitamin D and a hypocaloric diet in overweight and obese patients.
The recommendation for a hypocaloric diet can help patients with a body mass index of at least 25 kg/m2, according to the review. The duration to see benefit ranges from 16 weeks to 6 months, the authors write.
"Specifically, patients starting treatment with tumor necrosis factor blockers (etanercept, adalimumab, or infliximab) are significantly more likely to achieve minimal arthritis disease activity and to experience weight loss after a 6-month hypocaloric diet than after a regular diet," they write.
Ferris said that's one thing that jumped out at her with this study: it's not just the skin that seems to get better, but the joint disease as well, with a low-calorie diet.
"That means I really have good, concrete evidence to give my patients," she said. "I'm not just another doctor nagging them to lose weight."
Ford and colleagues found that although oral vitamin D supplements seem to be ineffective in improving skin disease severity, they may help for psoriatic arthritis.
"I think this is something that could be considered for patients with psoriatic arthritis," Ferris said. "That's a fairly easy thing to do."
The researchers note that it remains unknown whether a gluten-free diet can help improve psoriatic arthritis severity.
Patients Motivated to Try Dietary Changes
Evaluating the evidence behind dietary interventions is important because the subject is rarely discussed in patient visits, the authors say. Yet, such discussions could pay off because studies show that "patients with psoriasis are highly motivated to carry out dietary changes because these interventions are perceived to be natural, safe, and patient initiated," they write.
The authors emphasize that dietary changes should supplement medical therapies and not replace them.
"That's particularly important with psoriatic arthritis because delayed treatment of psoriatic arthritis can result in permanent, irreversible joint damage," Ferris said.
Multiple authors report various financial relationships with companies. A complete list of disclosures is available on the journal website. Ferris has disclosed no relevant financial relationships.