Fatty diets cause inflammation, impair cognitive function
A preclinical study led by the Walter and Eliza Hall Institute (WEHI) has found that even a few meals high in saturated fats can cause inflammation in the body, despite physical symptoms potentially taking years to appear. The landmark findings, published in the journal Immunity, are understood to be the first to show how rapidly the foods we eat can impact our gut defences.
About one in three Australians currently lives with chronic inflammatory disease — such as coeliac disease, inflammatory bowel disease and rheumatoid arthritis — but how this inflammation arises and causes disease remains largely unknown. Dr Cyril Seillet, a senior author on the new paper, said its findings could help pinpoint how chronic inflammation occurs at the source.
“We’ve shown that every meal we consume actively shapes our gut health,” Seillet said.
“The more saturated fats we eat, the more inflammation that builds up — gradually weakening our gut defences and increasing our susceptibility to chronic inflammation.
“But this inflammation build-up is initially silent, remaining hidden in our bodies until years later, where it can present as chronic inflammation.”
Researchers were able to detect microscopic changes to the gut health and function in mice even after a few high-fat meals, despite the mice lacking any visible symptoms of inflammation, such as weight gain.
“This shows how easily inflammation can develop without immediate warning signs,” Seillet said.
“While occasional high-fat meals won’t impair your gut protection barrier, a consistent diet that is high in saturated fats is laying the foundation for chronic gut inflammation to present in future.”
The researchers also found that short-term exposure to high-fat diets can reduce the production of interleukin-22 (IL-22), a crucial protein that helps control gut inflammation. This means that high-fat diets are a double hit to our gut barrier, said first author Le Xiong — because they not only promote inflammation, but also disable the body’s ability to fight it.
“IL-22 is a critically important protein for gut health and protection. Without it, the gut loses its ability to prevent inflammation,” Xiong said.
“It took only two days of consuming high-fat foods for the mice to lose their IL-22 stores and have an impaired gut function.
“Despite their gut protection capabilities being stripped away, the mice still looked healthy — highlighting how gut health can be compromised long before any visible symptoms appear.”
The researchers were able to rebuild the gut function of the mice in the study by restoring their IL-22 levels, highlighting the potential of creating a therapeutic intervention that can also restore gut health in humans. But they want to first focus on ways to naturally boost IL-22 level — and have already observed that unsaturated fats, like those found in nuts and avocados, can boost the protein’s production. This shows the importance of incorporating unsaturated fats into our diets.
The news comes after a separate study, led by The University of Sydney, linked fatty, sugary diets to impaired brain function, building on a growing body of evidence showing the negative impact of high-fat, high-sugar (HFHS) diets on cognitive ability. Published in the International Journal of Obesity, the research is the first to test in humans the relationship between HFHS diets and spatial navigation, which is the ability to learn and remember a path from one location to another.
The research team recruited 55 university students aged between 18 and 38, each of whom completed questionnaires capturing their intake of sugary and fatty foods. They also had their working memory tested in a number recall exercise, and their body mass index (BMI) recorded.
The experiment itself required participants to navigate a virtual reality maze and locate a treasure chest six times. The maze was surrounded by landmarks that participants could use to remember their route. Their starting point and the location of the treasure chest remained constant in each trial.
If participants found the treasure in less than four minutes, they continued to the next trial. If they failed to find the treasure in this time, they were teleported to its location and given 10 seconds to familiarise themselves with that location before the next trial.
A seventh trial removed the treasure chest from the virtual maze but asked participants to find and mark its former location based purely on memory. Those with lower levels of fat and sugar in their diets were able to pinpoint the location with a higher degree of accuracy than those who consumed these foods multiple times a week.
“After controlling for working memory and BMI, measured separately to the experiment, participants’ sugar and fat intake was a reliable predictor of performance in that final, seventh, test,” said research leader Dr Dominic Tran.
The research found that HFHS diets have a detrimental effect on some aspects of cognitive function. It is likely that these effects centre on the hippocampus — the brain structure that facilitates spatial navigation and memory formation — rather than acting across the entire brain.
“The good news is we think this is an easily reversible situation,” Tran said. “Dietary changes can improve the health of the hippocampus, and therefore our ability to navigate our environment, such as when we’re exploring a new city or learning a new route home.”
Tran said we already know that eating too much refined sugar and saturated fat hastens the onset of age-related cognitive decline in middle age and older adults, but this research “gives us evidence that diet is important for brain health in early adulthood — a period when cognitive function is usually intact”.
Tran acknowledged that the sample group used in this research was not representative of the wider population, as it’s likely the participants were a little healthier than the general population.
“We think, if our sample better represented the public, the impact of diet on spatial navigation would likely be even more pronounced,” he said.
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