"Our results suggest that diet may be a significant influencer of resistance to infectious disease through effects on the gut microbiota and immune system," lead author Dr. Cormac Gahan explained. "This has important implications for human health, especially during pregnancy, in old age and in immunocompromised individuals. It also has more general implications for research on infectious disease."
Infection caused by L. monocytogenes, better known as listeriosis, is considered a serious and severe condition. The condition is rare – in the U.S., only 1,600 people are affected each year – but it is deadly: According to the Centers for Disease Control and Prevention, about one in five people with listeriosis die and at least 20 percent of pregnant women infected with Listeria will end up with fetal loss or newborn death. This high mortality rate makes the infection a significant public health concern around the world.
In the study, the team investigated how a high-fat diet increased the risk of listeriosis using a murine model. The results were telling: Mice treated with a high-fat diet, including those who were just fed short-term, experienced significant changes in their gut microbiota. This change in the microbiota, which also promoted a pro-inflammatory gene expression in the host, increased the host's susceptibility to an oral L. monocytogenes infection. A high-fat diet also resulted in elevated levels of Firmicutes in the gut microbiota. Studies show that Firmicutes, together with Bacteroidetes, is closely associated with obesity. In particular, a study in the Archives of Medical Science found elevated levels of the two in the fecal microbiota of obese children.
"Short-term consumption of the high-fat diet increased levels of Firmicutes bacteria in the gut which are associated with obesity," noted Vanessa Las Hera, a doctorate student at UCC and a co-author of the study. "The effects of [the high-fat] diet were also seen beyond the gut, with reduced levels of immunity throughout the body, local alterations to gastrointestinal cell function and changes to the gut microbiota that enhanced the progression of Listeria infection."
The composition of the gut microbiota changed further after getting listeriosis. However, the researchers observed that inflammatory responses from the host that target the infection were downgraded, which indicated an impaired response in the context of the high-fat diet. Researchers noted that the adverse effects of eating a high-fat diet even affected the liver, as it increased the sensitivity of mice to systemic infection and caused changes in gene expressions in the liver. (Related: Antibiotic era ending - Antimicrobial pecan shell extract can prevent Listeria contamination in organic meats.)
In another groundbreaking study published in The Lancet, researchers concluded that Western-type diets, which are high in salt and fat and low in fiber and fruit, caused more deaths globally than smoking and high blood pressure. The analysis-comparing diet, which compared death and disease rates across 195 countries, indicated that around a fifth of all deaths in the world can be traced back to unhealthy eating, itself a major risk factor for cardiovascular disease, diabetes, and cancer.
In particular, changing dietary habits – which leaned on eating more meat and having fewer vegetable staples – and the rapidly increasing amount of fast food were identified to be some of the main drivers for poor diets. Learn more about how red meat and sugary drinks increase the risk of developing gout.
The numbers are staggering: In 2017, over 11 million deaths (22 percent of total recorded deaths) were a result of poor diet. In comparison, tobacco- and smoking-related deaths accounted for only eight and 10 million deaths, respectively. Researchers analyzed these figures and found that a diet high in sodium and low in whole grains and fruits accounted for over half of the deaths. The remaining deaths were caused by high consumption of red and processed meat, sugar-sweetened drinks, and other unhealthy foods.
"Poor dietary habits are associated with a range of chronic diseases and can potentially be a major contributor to [non-communicable disease] mortality in all countries worldwide," the researchers wrote in their report. "Given the complexity of dietary behaviors and the wide range of influences on diet, improving diet requires [the] active collaboration of a variety of actors throughout the food system."