- A new study in mice suggests that a high sugar, moderate fat diet causes imbalance in the gut microbiome and promotes inflammation in the skin and joints.
- Switching to a balanced diet can reverse the inflammatory effects and increase microbiome diversity.
A recent study in mice led by researchers at the University of California (UC) Davis School of Medicine found that an imbalanced diet may further exacerbate inflammatory skin conditions by way of the gut microbiome.
The study appears in the Journal of Investigative Dermatology.
Psoriasis is an autoimmune skin condition that also involves inflammation. It manifests with itching, rashes, and scaly patches on the skin.
While psoriasis is fairly common, there is no permanent treatment. Around 30% of people with psoriasis may develop joint pain and swelling in the form of psoriatic arthritis.
Diet is known to influence the skin’s susceptibility to inflammation. It also plays a role in maintaining the homeostasis of the gut microbiome community.
The gut microbiota consists of trillions of microorganisms that, when out of balance, can make the body more susceptible to disease and infection.
For the present study, the researchers used a mouse model and split the mice into two diet groups: one group received a “chow diet”, while the other was fed a “Western diet.”
The study defines Western diet as “a high sugar and moderate fat diet”, as opposed to a chow diet, which is considered a standard, balanced diet for mice.
After 6 weeks of the respective diets, the researchers injected a number of mice from each group with DNA of the interleukin-23 (IL-23) cytokine protein. IL-23 is a protein involved in the inflammatory response, and it is linked to many inflammatory conditions.
The researchers then continued to feed the respective diets to the mice for an additional 4 weeks, for a total of 10 weeks.
At the 6-week mark, the researchers found that the mice eating a Western diet gained more weight compared with the mice fed a chow diet.
At the 10-week mark, the mice group that was fed a Western diet and injected with IL-23 DNA displayed skin inflammation — indicated by signs of red, scaly patches on their skin and ear swelling — along with joint inflammation.
In the chow diet-fed mice injected with IL-23 DNA, these signs were present to a lesser extent. The mice that did not receive the IL-23 DNA injection did not experience any of these symptoms.
Additionally, while the presence of IL-23 DNA promoted the expression of psoriasis-related cytokines in both diet groups, this was further exacerbated in the mice fed a Western diet.
These results suggest a Western diet heightens the functions of the IL-23 cytokine to increase inflammatory levels.
The study also raised a question of whether IL-23-mediated inflammation was linked to the gut microbiota, since both are influenced by diet.
The researchers examined the abundance and depletion of microbial species induced with high IL-23 levels in the mice following a Western diet. They found that these factors worked “in a synergistic manner” to lower the diversity of the microbiome.
In one experiment, they transmitted microbes between Western diet-fed mice injected with IL-23 DNA and a new, untested group of mice. After this microbial transmission, the new mice displayed higher levels of pro-inflammatory cytokines.
The study concludes that an imbalanced diet may cause microbial imbalance, which heightens the inflammatory effects that are already present with IL-23 overexpression.
“There is a clear link between skin inflammation and changes in the gut microbiome due to food intake,” said Dr. Samuel Hwang, lead study author and professor in the Department of Dermatology at UC Davis.
“The bacterial balance in the gut disrupted shortly after starting a Western diet and worsened psoriatic skin and joint inflammation.”
The good news is the effects of a short-term Western diet were not permanent and could be partially reversed.
After 6 weeks of a Western diet, some of the mice were switched onto a chow diet for the remainder of the 10 weeks.
They demonstrated a decrease in skin scaling, ear thickness, and levels of inflammatory cytokines compared with the mice that continued on a Western diet. They also showed a greater abundance of microbial diversity.
Antibiotics were also able to reduce skin inflammation in the Western diet-fed mice.
The study shows that an imbalanced diet could exacerbate the expression of IL-23, which leads to downstream effects of increasing inflammatory cytokines and can decrease microbial diversity.
Ultimately, these factors can cause skin and joint inflammation in the form of psoriasis. However, switching to a more balanced diet could ameliorate these effects of the condition.
“It was quite surprising that a simple diet modification of less sugar and fat may have significant effects on psoriasis,” noted study author Zhenrui Shi, a researcher in the UC Davis Department of Dermatology.
“These findings reveal that patients with psoriatic skin and joint disease should consider changing to a healthier dietary pattern.”
As an alternative, the researchers suggest the possibility of directly targeting the gut microbiota to address psoriasis.
Further research is needed to understand the mechanisms of the inflammatory cytokines and their interactions with the gut microbiome.