Certain saturated fats that are common in the modern Western diet can initiate a chain of events leading to complex immune disorders such as inflammatory bowel diseases, say US medicos in the journal Nature. The researchers, from the University of Chicago, say the finding helps explain why once-rare immune-mediated diseases have become more common in westernized societies in the last half century.
Importantly, the researchers found that concentrated milk fats, which are copious in processed and confectionary foods, alter the composition of bacteria in the intestines. These changes, the researchers say, can disrupt the delicate relationship between the immune system and the largely beneficial mix of bacteria in the intestines. The emergence of harmful bacterial strains in this setting can unleash an unregulated tissue-damaging immune response that can be difficult to switch off.
"This is the first plausible mechanism showing step-by-step how Western-style diets contribute to the rapid and ongoing increase in the incidence of inflammatory bowel disease," said study author Eugene B. Chang.
Why would milk fat - a powdered substance that remains when fat has been separated from butter and dehydrated - trigger inflammation when polyunsaturated fat did not? The researchers traced the answer to the complex mix of hundreds of bacterial strains that reside in the bowels.
Chang and his co-researchers found that an uncommon microbe called Bilophila wadsworthia was preferentially selected in the presence of milk fat. Previous studies had found high levels of B. wadsworthia in patients with appendicitis and other intestinal inflammatory disorders, including inflammatory bowel disease. "That piqued our interest," Chang said. "These pathobionts, which are usually non-abundant, seem to be quite prominent in these diseases."
He added that while B. wadsworthia levels were almost undetectable in mice on a low-fat or unsaturated-fat diet, the bacteria made up about 6 percent of all gut bacteria in mice fed a high milk-fat diet. "Here we show how the trend in consumption of Western-type diets by many societies can potentially tip the mutualistic balance between host and microbe to a state that favors the onset of disease," Chang said.
Much of the recent progress in understanding the biology of inflammatory bowel disease has focused on gene variants that can increase risk. But the new study puts the focus on changing environmental factors that might trigger the disease in high-risk patients.
"Right now we can't do much about correcting genes that predispose individuals to increased risk for these diseases," Chang said, "however, the balance between host and microbes can be altered back to a healthy state to prevent or treat these diseases. In essence, the gut microbiome can be 're-shaped' in sustainable and predictable ways that restore a healthy relationship between host and microbes, without significantly affecting the lifestyles of individuals who are genetically prone to these diseases. We are testing that right now."
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Source: University of Chicago Medical Center