Swapping a Western diet for a healthy, balanced diet may reduce skin and joint inflammation while improving gut health in people with psoriasis, a new study in mice suggests.
In the study, a Western diet caused immune cells to migrate into mice skin and joints, where they released inflammatory proteins that caused redness and swelling in the skin around the ears and digits. It also reduced the diversity and amounts of beneficial gut bacteria.
Switching from a western diet to a healthy diet significantly improved redness, swelling, and beneficial gut bacteria quantities within a short duration.
The study, “Short-Term Western Diet Intake Promotes IL-23-Mediated Skin and Joint Inflammation Accompanied by Changes to the Gut Microbiota,” was published in the Journal of Investigative Dermatology.
Psoriasis is an inflammatory disorder of the skin.
It occurs when skin cells called keratinocytes begin to grow and multiply uncontrollably, forming dry, thick, red silvery scales that appear on the scalp, back, knee or elbow. Psoriasis can also affect the joints and eyes and currently has no cure.
Diet potentially contributes to psoriasis severity since rodent studies show that diets rich in saturated fat cause psoriasis flare-ups, while low saturated fat diets prevent them. More recent studies show that Western diets, typically high in sugar and saturated fat, promote skin inflammation.
Diet also influences the types and quantities of bacteria in the gut.
A western diet encourages gut bacteria imbalances, causing a rapid decline in the diversity and quantities of beneficial gut bacteria – gut dysbiosis – leading to inflammation and poor immunity.
Since diet influences skin inflammation and gut dysbiosis, a team of researchers used a mouse model of psoriasis to investigate how diet affects skin and joint inflammation in psoriasis and whether gut dysbiosis plays a role in its severity.
For six weeks, the researchers fed mice a Western diet or a healthy diet. After six weeks on the diets, they injected mice with an inflammatory protein – interleukin (IL)-23 – causing them to develop psoriasis-like skin and joint symptoms. Mice maintained their diets (Western or healthy) for an additional four weeks.
Mice eating the Western diet developed severe ear swelling, redness, and skin scaling after ten weeks. In contrast, mice eating a healthy diet experienced significantly milder ear swelling, skin redness and scaling.
Western diet-fed mice also had significantly higher numbers of inflammatory immune cells and proteins in their skins and joints than those fed the healthy diet indicating that the Western diet worsened psoriasis-related skin and joint inflammation.
Furthermore, when their gut bacteria were analysed, the researchers found that compared with the mice fed healthy diets, Western diet-fed mice had lower bacteria diversity and high quantities of bacteria species associated with obesity, such as Firmicutes.
“There is a clear link between skin inflammation and changes in the gut microbiome due to food intake,” Sam Hwang, Professor and Chair of Dermatology at the University of California – Davis Health and senior author on the study, said in a press release. “The bacteria balance in the gut disrupted shortly after starting a Western diet and worsened psoriatic skin and joint inflammation,” he added.
The researchers went on to test if switching from a Western diet to a healthy diet could reduce skin and joint inflammation and restore gut bacteria balance. To do this, they fed mice a Western diet for six weeks before injecting them with IL-23 to initiate psoriasis-like disease. The. Mice were then divided into four groups, a group that continued the western diet for another four weeks and a group that switched to the healthy diet for the same duration.
Interestingly, switching from a Western diet to a healthy diet for four weeks significantly reduced ear swelling, skin redness and scaling, and the quantities of inflammatory cells and proteins in skins and joints. It also altered the gut bacteria composition, increasing diversity and reducing the amounts of Firmicutes.
“It was quite surprising that a simple diet modification of less sugar and fat may have significant effects on psoriasis,” Zhenrui Shi, lead author on the study, said. “These findings reveal that patients with psoriatic skin and joint diseases should consider changing to a healthier dietary pattern,” she added.
The study highlights the link between diet, gut health and skin and joint inflammation in psoriasis. A healthy diet promoting gut health may be beneficial in reducing psoriasis severity.
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