A study that is bound to further exacerbate the “controversy” of high-fat diets (HFD) vs. low-fat diets (LFD) and their role in chronic inflammatory diseases (in this case psoriasis and lung inflammation). Yet, the study findings are unequivocal. Namely, even a brief (4-day) exposure dramatically exacerbated the inflammatory response to a skin irritant and imprinted some sort of “cell memory” so that when the subjects were primed again with a skin irritant, the inflammatory response was much worse compared to subjects kept on a low-fat diet, even when the challenge was initiated long after the initial exposure to the HFD. Interestingly, it was the diet, not how obese the subjects were at the time of challenge and re-challenge, that determined the severity of the inflammatory response. Feeding the subjects increased levels of glucose did NOT induce the inflammatory response nor did it imprint the inflammatory “memory” to be reactivated at subsequent inflammatory challenge. This study may explain why many people who are of normal weight or even skinny, often develop chronic inflammatory conditions, while others, who are obese, remain symptom-free despite their elevated BMI. It is all about the diet, we truly are what we eat. And last, but not least, the study tested whether weight loss drugs of the GLP-1 agonist category (Ozempic Wegovy, Mounjaro, etc) could prevent the inflammatory response. They did not, which is yet another indication that those drugs are little more than a symptomatic treatment, with no long term benefit for the underlying issue, which once again has been found to be inflammation.
https://www.nature.com/articles/s41586-026-11181-4
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Diet, not body mass, dictates disease
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“…Transient exposure to HFD during a narrowly defined peri-initiation window durably reshapes tissue immunity without requiring obesity. The consequence is not merely heightened acute pathology but a lasting change in local immune responsiveness that becomes evident months later after rechallenge, after return to LFD. These experiments identify dietary state, rather than accumulated adiposity, as the proximate determinant of disease amplification. Three compositionally distinct fat-enriched diets—HFD, MFD and WD—each amplified IMQ-induced type 17 skin inflammation, whereas glucose water alone did not. Conversely, transiently switching persistently obese mice from HFD to LFD during a corresponding four-day peri-initiation window attenuated disease. Semaglutide further sharpened this dissociation: GLP-1 receptor agonism improved glucose handling, reduced body weight and adiposity, and lowered circulating insulin and leptin, but did not attenuate HFD-amplified inflammatory responses. Although longer-term treatment with GLP-1 receptor agonists and related incretin-based therapies may improve established psoriasis in patients with obesity or type 2 diabetes44,45,46,47, our experiment addressed the distinct question of whether short-term semaglutide treatment blocks the additional amplification imposed by coincident HFD exposure. It did not, indicating that systemic metabolic improvement and diet-primed inflammatory susceptibility are separable. Whereas prolonged high-fat or Western-style feeding has previously been shown to exacerbate IMQ-induced and IL-23-driven inflammation48,49,50 and, with sustained exposure, promote spontaneous dermatitis23,24, as little as 4 days at inflammatory onset was sufficient here. HFD alone did not confer durable susceptibility to a later inflammatory challenge, indicating that dietary exposure must intersect with tissue inflammation to imprint the long-term phenotype. Our findings may also help explain a previous observation that leptin-deficient ob/ob mice did not exhibit increased IMQ susceptibility despite profound adiposity49. As leptin supports optimal TH17 differentiation51, its absence may limit engagement of the IL-1β–TH17 axis. Consistent with this possibility, transient peri-initiation HFD amplified IMQ-induced inflammation in WT but not ob/ob mice (Extended Data Fig. 2o).”
“…Scientists have long known that diet shapes the immune system. Now, a UC San Francisco team has found that even a brief dietary change can substantially change how the body responds to skin irritation, at least in mice. When scientists fed mice a high-fat diet for just a few days, the mice had a much worse reaction to an irritating cream. And the skin stayed on alert even after the mice returned to a low-fat diet and inflammation cleared, responding more strongly the next time it was exposed to the cream. The findings suggest that short-term diet may have just as much effect as body weight when it comes to inflammation. “Long-term dietary habits absolutely matter for health, but our study unearthed a much more real-time influence of diet,” said Sagar Bapat, MD, PhD, professor of pathology at UCSF and corresponding author of the paper, which appears in Nature on Oct. 28. “Breakfast, lunch, dinner — they all can have a tremendous and rapid impact on the immune system.”
“…“For many years, we’ve known that obesity is tied to more severe inflammation. But we wanted to know whether it was the extra weight or simply the bad diet that was driving the stronger response,” Jiang said. So, the team tested whether just four days on high-fat food was enough to trigger an over-active immune response. They switched mice that had been raised on low-fat food to high-fat food, and dabbed one ear with imiquimod three days later. The normal-weight mice developed severe ear inflammation just like the obese mice. Likewise, obese mice that had been switched to normal food for four days experienced much milder inflammation. Weeks later, after the normal-weight mice had returned to a low-fat diet and their inflammation had subsided, they got a second dose of imiquimod in the same ear that had flared before — and it triggered an outsized response. Jiang and Bapat found that high-fat food drew rapid-response immune cells into the skin, where they amplified the reaction to imiquimod. As the inflammation subsided, other immune cells, called memory T cells remained in the affected ear. Together, these changes left the tissue primed for the next time. The team found a similar kind of heightened inflammation in response to irritation in the lungs after just a few days of eating a high-fat diet. “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,” said Jiang. “Diet, exercise, sleep — they could all shape immune health in ways we don’t yet appreciate.”
