Switching diet promotes healthy skin and joints, say scientists

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Around 30% of patients with psoriasis also develop psoriatic arthritis with symptoms such as joint pain, stiffness and swelling.

“The Western Diet (WD), in particular, can lead to a rapid and detrimental impact on microbial community and function, contributing to systemic inflammation and other metabolically compromised phenotypes,” ​the authors write.

Among the numerous factors known to influence gut microbiota composition, dietary composition has repeatedly been shown to be one of the most critical modifiable factors regulating the gut microbiota.”

Changing the odds

Tests have shown that a diet rich in sugar and fat induce spontaneous skin inflammation and therefore increase the odds of developing psoriasiform dermatitis (PsD). Gut microbiota is known to play a key part in controlling inflammation. Disruption of gut microbiome by external factors, such as a poor diet, promotes overproduction of harmful pathogens, destabilizes the immune system, and subsequently leads to inflammatory disease.

“Perturbation of the gut microbiome by environmental factors such as diet promotes the overgrowth of harmful pathobionts, disrupts immune homeostasis, and leads to the development of inflammatory diseases,” ​they explain.

The team used a mouse model to study the effects of WD on microbial imbalance (dysbiosis) and associated skin and joint inflammation. They also analysed whether dietary changes could reverse symptoms of dysbiosis.

Study protocol

The study included two groups of mice that were exposed to a short-term WD or Chow diet (CD) and subsequently injected with 10 μg of interleukin-23 minicircle DNA (IL-23 MC DNA) – a protein linked to inflammatory autoimmune reactions – to induce psoriasis-like skin and joint conditions. The effects of IL-23 exposure were analysed and the results recorded.

Initial findings revealed the CD-fed group developed psoriatic inflammation but presented no other noteworthy symptoms. However, the second group (fed a WD) developed severe gut problems and the majority perished after two weeks. The IL-23 MC DNA dose was halved as a result, to ensure the WD-fed mice would tolerate treatment.

After a further six weeks on their respective diets the two groups were injected with IL-23 MC DNA or with a control. Their diets were maintained for another four weeks.   

Dietary symptoms

The researchers noted that after six weeks (before MC DNA delivery) the mice on the WD gained more weight than CD-fed mice and at 10 weeks WD intake led to higher weight gain in the control group. There was no significant weight gain in the IL-23 MC DNA treated mice.

Erythema (skin rash) and scaling were observed in the WD + IL-23 MC DNA group but were considerably milder in the CD + IL-23 MC DNA group and absent in the control. The control group also exhibited the least amount of ear swelling.

The data suggests that a WD can lead to increased intestinal permeability (or leaking gut), which has previously been observed in autoimmune diseases, including psoriasis. A loss of microbial diversity was also observed in WD-fed mice. Thus, the authors surmise that modulating gut microbiota was a viable option to help regulate intestinal permeability and control psoriatic inflammation. 

Restorative effects

Crucially, the researchers observed that a more balanced (CD) diet helped reduce gut dysbiosis and helped restore some balance to the gut microbiome.

Mice that were switched from a WD to a CD after 10 weeks had less scaling and reduced ear and epidermal thickness, compared with those that remained on the WD.

The researchers therefore concluded that the proinflammatory effects of a WD could be partially reversed with dietary changes.

Source: Journal of Investigative Dermatology

Authors: Zhenrui Shi, Xuesong Wu, Clarissa Santos Rocha, Yu-Jui Yvonne Wan, Satya Dandekar, Samuel T. Hwang

“Short-Term Western Diet Intake Promotes IL-23-Mediated Skin and Joint Inflammation Accompanied by Changes to the Gut Microbiota in Mice”

doi.org/10.1016/j.jid.2020.11.032

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