In direct contradiction to current thinking on nutritional guidance for psoriasis, study data published in The Journal of Dermatology reported that “psoriasis was associated with high body mass index (BMI) and a low intake of red meat.”

The prospective study included 70 adult patients with psoriasis showing plaque-type scaly erythema (46 men), diagnosed clinically and histologically. A subset of 17 patients with psoriatic arthritis was also identified.

The investigators point out that effect of the Japanese diet, consisting primarily of rice, soy-based miso soup, and fish and other products from the sea, may contribute to psoriasis as much as the Western diet high in fat and red meat. Consistent with Western studies, the investigators found a direct correlation to high BMI in patients with psoriasis but in a startling reversal of food factors, Japanese patients with psoriasis also consumed greater amounts of fish and pulses (nutrient-dense edible seeds from legumes) and lower quantities of red meat, compared with control patients.

The authors suggested the reasons for these differences could simply reflect natural ethnic preferences or intentional modifications designed to reduce the severity of existing psoriasis symptoms.

Both the high-fat Western diet and the high consumption of sweeteners in the Japanese diet are associated with insulin resistance. Japanese patients with psoriasis also consumed higher than normal amounts of sugar and artificial sweeteners known to promote inflammation compared with control patients, while the authors observed that patients from US cohorts tended to consume lower than normal amounts of sweeteners.

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The authors observed that a diet high in confectionary substances including baked goods, candy, and sugar-sweetened sodas and low in consumption of fruits and vegetables has been associated with high levels of pro-inflammatory adipokines such as leptin. Increased sugar intake may aggravate the severity of psoriasis and increase the risk for cardiometabolic disorders that often also occur in these patients.

At the same time, intake of beta carotene and vitamin A and consumption of green and yellow vegetables was greater among Japanese patients with psoriatic arthritis compared with people who did not have psoriatic arthritis. The researchers suggested this may contribute to psoriasis pathology through mechanisms involving rapid acceleration of osteoblast differentiation and ossification of mesenchymal stem cells.

“The significance of these results in the pathogenesis of psoriatic skin and joint lesions” suggest the need for further study, the investigators wrote.

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Reference

Yamashita H, Morita T, Ito M, et al. Dietary habits in Japanese patients with psoriasis and psoriatic arthritis: Low intake of meat in psoriasis and high intake of vitamin A in psoriatic arthritis. J Dermatol. 2019 Sep;46(9):759-769.