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Does a Western diet affect the risk of chronic gut infection?

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New research in mice examines the effects of a Western diet on colon health. Dulin/Getty Images
  • Diets that are high in fat and low in fiber reduce the number of bacteria in the gut, which may increase the risk of inflammatory bowel disease, metabolic syndrome, and cancer.
  • One benefit of a healthy gut microbiota is that it protects the large intestine from colonization by pathogenic bacteria, such as Escherichia coli.
  • In a new study in mice, researchers found that a Western-style diet frequently led to more persistent infections.
  • Mice with persistent infections were also more likely to have insulin resistance months after the initial infection.

The community of microorganisms that lives in the human gut, known as the gut microbiome, provides a wide range of “services” to its hosts.

Most of the microbes live in the large intestine, where they feed on fiber that has passed undigested through the earlier parts of the digestive tract.

Some scientists believe that a Western-style diet, which is high in fat and simple carbohydrates but low in fiber, may provide insufficient quantities of fiber to support a diverse gut microbiome and its health benefits.

For example, they cite evidence that highly processed, low fiber diets are associated with an increased prevalence of inflammatory bowel disease, metabolic syndrome, and cancer.

Another health benefit that the gut microbiota provides is to defend the large intestine against colonization by disease-causing bacteria, such as Salmonella and Clostridium difficile.

These hidden defenses only become apparent after a course of antibiotics, which, by disrupting the gut microbiota, can make hospital patients more vulnerable to infection with potentially life threatening pathogens.

A team of researchers at Georgia State University in Atlanta speculated that the colons of people who eat a Western-style diet might be more prone to colonization with foodborne bacteria, such as pathogenic strains of E. coli.

When the scientists tested their hypothesis in mice, they were surprised to discover that a Western-style diet reduced the initial colonization of the animals’ large intestines by a disease-causing bacterium.

“However, mice consuming the Western-style diet frequently developed persistent infection that was associated with low grade inflammation and insulin resistance,” says Andrew Gewirtz, Ph.D., who is a professor at the university’s Institute for Biomedical Sciences and senior co-author of the study.

Insulin resistance is an early sign of type 2 diabetes.

The research appears in the journal PLOS Pathogens.

The scientists studied the effect of a Western-style diet on the colonization of the large intestine by the bacterium Citrobacter rodentium in mice.

Prof. Gewirtz told Medical News Today that researchers often use C. rodentium to model human gut infections with E. coli.

The two species are similar genetically and metabolically, he said, and both cause acute inflammation through very similar mechanisms.

“Hence, we speculate our findings predict how diet would impact E. coli in humans, but [we] are not aware of any findings to directly address this,” he said.

Compared with the usual, grain-based lab chow, eating a Western-style diet led to a rapid decrease in the number of bacteria in the animals’ feces.

When the team laced the animals’ feed with C. rodentium, there was a modest reduction in the initial colonization of the gut by the bacterium and decreased acute inflammation in the mice on the Western-style diet. However, these results were not statistically significant.

“Yet, the most striking consequence of [Western-style diet] consumption was frequent inability of mice to clear this pathogen,” the researchers write in their paper.

All the mice that ate a grain-based diet cleared the bacterium from their gut within 3 weeks of the initial infection, but 40% of the mice that ate a Western-style still had the infection 8 weeks later.

The mice in the grain-based diet group were also completely resistant to reinfection with C. rodentium. By contrast, those that ate the Western-style diet and initially recovered from the infection were prone to repeat, chronic infections with the bacterium.

In addition, the scientists found some evidence of insulin resistance and low grade inflammation in the mice on the Western-style diet that developed a chronic C. rodentium infection. However, the low grade inflammation was not statistically significant.

The principal limitation of the study is that it investigated colonization by pathogens in mice eating two different diets, which may not reflect what happens in humans.

However, the study demonstrates the complexity of the effects of diet on the gut microbiota and the possible knock-on effects on human health.

One of the greatest challenges facing humanity is the inexorable rise of antibiotic resistance in disease-causing bacteria.

According to David Weiss, Ph.D., Director at the Emory Antibiotic Resistance Center at Emory University School of Medicine, GA, there is no evidence that a Western-style diet promotes antibiotic resistance in pathogenic gut bacteria.

However, he told Medical News Today that the potential health benefits from a deeper understanding of the human microbiome are likely to be far-reaching.

“Ten years from now, if we look back and say, ‘what was overall the biggest development in medicine?’, it would be understanding the microbiome and harnessing the microbiome to treat disease,” he said.

“It’s so unbelievably complex, but it’s also amazing.”

What do you think?

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