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Just Four Days Of High-Fat Diet May Increase Inflammation, Study Finds

High Fat Foods And Their Impact On Health

Long-term <span>diet and obesity</span> are known to affect <span>inflammation</span>. A new study from the University of California, San Francisco suggests that even a few days of eating differently can change how strongly the <span>immune system</span> reacts, at least in mice.

The study was published in Nature on October 28. It was led by Sagar Bapat, a professor of pathology at UCSF and the paper’s corresponding author. Zewen “Owen” Jiang, who did the work as a graduate student at UCSF, was co-first author, according to UCSF.

The team raised mice on either low-fat or high-fat food pellets. They then applied imiquimod, a cream that triggers skin inflammation, to one ear of each mouse. Mice raised on high-fat food and made obese had severe reactions, while mice on low-fat food had mild ones.

Obesity has long been tied to more severe inflammation, but it wasn’t clear why. “We wanted to know whether it was the extra weight or simply the bad diet that was driving the stronger response,” Jiang said.

To find out, the researchers switched normal-weight mice from low-fat to high-fat food for just four days, then applied the cream three days later. These lean mice developed severe ear inflammation, just like the obese mice. In the other direction, obese mice moved to normal food for four days had much milder inflammation.

The paper’s conclusion is that the dietary state around the time inflammation starts, rather than obesity itself, determines how severe the disease gets.

Weeks later, the normal-weight mice were back on low-fat food and their inflammation had cleared. The researchers applied the cream again to the same ear. The reaction was far stronger than expected.

The researchers found that high-fat food drew rapid-response immune cells into the skin, which amplified the reaction. As the inflammation faded, memory T cells stayed behind in the ear. Together, these changes left the tissue primed for the next flare-up, UCSF reported. The paper also found that the response depends on CD4+ T cells, and that a protein complex called NLRP3 drives the diet-amplified disease.

The team saw a similar heightened response in the lungs after a few days on a high-fat diet.

Also Read: <a href="https://www.healthandme.com/health-wellness/psoriasis-understanding-the-skin-condition-and-ways-to-manage-flare-ups-article-156433812" data-type="tilCustomLink" target="_blank">Psoriasis: Understanding The Skin Condition And Ways To Manage Flare-ups</a>

“Long-term dietary habits absolutely matter for health, but our study unearthed a much more real-time influence of diet,” Bapat said. “Breakfast, lunch, dinner, they all can have a tremendous and rapid impact on the immune system.”

Jiang added a note of caution. “The diet of a laboratory mouse doesn’t map neatly onto what we eat, but it’s striking how quickly the immune system responds to what’s happening in the body right now,” he said. “Diet, exercise, sleep, they could all shape immune health in ways we don’t yet appreciate.”

<h2>What this does and doesn’t mean</h2>

This was a study in mice, and the high-fat pellets used in the lab are not the same as human meals. The findings don’t show that a single unhealthy meal will worsen a person’s skin or lung conditions. They do suggest that what is eaten around the time inflammation begins may matter more than researchers had assumed, and that the immune system may hold a memory of it.

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Long-term diet and obesity are known to affect inflammation. A new study from the University of California, San Francisco suggests that even a few days of eating differently can change how strongly the immune system reacts, at least in mice.What the researchers didThe study was published in Nature on October 28. It was led by Sagar Bapat, a professor of pathology at UCSF and the paper’s corresponding author. Zewen “Owen” Jiang, who did the work as a graduate student at UCSF, was co-first author, according to UCSF.The team raised mice on either low-fat or high-fat food pellets. They then applied imiquimod, a cream that triggers skin inflammation, to one ear of each mouse. Mice raised on high-fat food and made obese had severe reactions, while mice on low-fat food had mild ones.Is it the weight or the diet?Obesity has long been tied to more severe inflammation, but it wasn’t clear why. “We wanted to know whether it was the extra weight or simply the bad diet that was driving the stronger response,” Jiang said.To find out, the researchers switched normal-weight mice from low-fat to high-fat food for just four days, then applied the cream three days later. These lean mice developed severe ear inflammation, just like the obese mice. In the other direction, obese mice moved to normal food for four days had much milder inflammation.The paper’s conclusion is that the dietary state around the time inflammation starts, rather than obesity itself, determines how severe the disease gets.The skin rememberedWeeks later, the normal-weight mice were back on low-fat food and their inflammation had cleared. The researchers applied the cream again to the same ear. The reaction was far stronger than expected.The researchers found that high-fat food drew rapid-response immune cells into the skin, which amplified the reaction. As the inflammation faded, memory T cells stayed behind in the ear. Together, these changes left the tissue primed for the next flare-up, UCSF reported. The paper also found that the response depends on CD4+ T cells, and that a protein complex called NLRP3 drives the diet-amplified disease.The team saw a similar heightened response in the lungs after a few days on a high-fat diet.Also Read: Psoriasis: Understanding The Skin Condition And Ways To Manage Flare-upsWhat the scientists said“Long-term dietary habits absolutely matter for health, but our study unearthed a much more real-time influence of diet,” Bapat said. “Breakfast, lunch, dinner, they all can have a tremendous and rapid impact on the immune system.”Jiang added a note of caution. “The diet of a laboratory mouse doesn’t map neatly onto what we eat, but it’s striking how quickly the immune system responds to what’s happening in the body right now,” he said. “Diet, exercise, sleep, they could all shape immune health in ways we don’t yet appreciate.”What this does and doesn’t meanThis was a study in mice, and the high-fat pellets used in the lab are not the same as human meals. The findings don’t show that a single unhealthy meal will worsen a person’s skin or lung conditions. They do suggest that what is eaten around the time inflammation begins may matter more than researchers had assumed, and that the immune system may hold a memory of it.