Gut bacteria and gut fungi influence each other in a complex interplay, and a high-fat diet affects this dynamic, according to new research.
The researchers were led by Dr. Cheryl Gale, an associate professor in the Department of Pediatrics at the University of Minnesota in Minneapolis.
As Dr. Gale and her colleagues explain, previous research has shown that obesity is associated with changes in gut bacteria.
Most studies have therefore focused on how a high-fat diet alters the gut microbiome, leaving the role of gut fungi overlooked.
Studying gut fungi in mice
Dr. Gale and her team fed two groups of mice two different diets: a high-fat one and a normal one (the control group).
Mice that were fed a high-fat diet put on weight and displayed metabolic markers of obesity, such as insulin resistance.
Having analyzed the bacterial and fungal microbiota, the researchers found that the mice fed the high-fat diet had "significantly different" bacterial and fungal compositions than those fed a normal diet.
For instance, regarding the bacterial composition, the study found "an increase in Firmicutes and [a] decrease in Bacteroidetes in response to [a] high-fat diet." And as the authors explain, this is in accordance with previous findings.
Regarding fungi, the researchers found that the mice fed a standard diet had an increase in six fungal taxa. By comparison, no fungal taxa were found to have increased in the high-fat group.
Also, the number of so-called co-abundance correlations between certain fungi and bacteria decreased "dramatically" in the mice that were fed a high-fat diet, compared with those fed a standard diet.
The study authors conclude:
"[The] results of this study provide evidence that fungi and inter-kingdom interactions are disrupted by [a] high-fat diet, thus supporting the inclusion of fungal community analyses in studies that seek to discover new connections between intestinal microbiomes and metabolic health."
Gut fungi's role in obesity overlooked
"These results," the authors write, "suggest a role for fungi [...] in the association between gut microbiomes and obesity." Currently, over a third of adults in the United States are obese, and between 15 and 20 percent of U.S. children and teenagers have this metabolic disorder.
Dr. Gale notes that the role of fungi in understanding obesity has been neglected in the research community, and that the available study methods should reflect the need to pay more attention to fungi.
"The methods development hasn't caught up to where it is with bacteria. You need very sensitive methods because fungi are less abundant," she says. "We haven't developed the databases of sequences for fungi like we have for bacteria."
"We really need to be looking at all the microbes and how they are interacting with each other to get a full picture of what the microbiome structure and function is in a given individual," explains Dr. Gale.
"Not only are we affecting the community of fungi with dietary change," she adds, "but we also see that relationships between fungi and bacteria are changing."
"These kingdoms are not in isolation. If one changes, it is going to impact the community structure and maybe the functional structure of other kingdoms as well. I think that is where the microbiome field is moving," concludes Dr. Gale.