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Obesity has been called a non-infectious pandemic. Fifteen per cent and 22 per cent of Canadian and American children and adolescents are classified as obese, respectively. Obesity is associated with , and childhood obesity increases the risk of obesity later in life.

Many studies have shown that bacteria in the intestinal microbiome — the community of microbes in the human gut — play an important role in metabolism. Research has found strong associations between infant gut microbiome composition, infant growth trajectories, and the risk of becoming overweight or obese. However, little is known about the role that gut fungi, known as the mycobiome, play in early childhood health and development.

New discovery indicates gut fungi affect metabolism

Now, a led by researchers in the (CSM) at the ��ݮ����Ƶ���� has found a link between the diversity, or number, of fungal species in the infant gut and the body-mass index (BMI) of infants.

“The pattern of fungal diversity was being reflected in the metabolism, or the body weight, of these children,” says Dr. Marie-Claire Arrieta, PhD, associate professor in at the Cumming School of Medicine and principal investigator on the study. Along with changes in fungal diversity, the study found other contributing factors related to infant BMI. These included the BMI of the mother and her diet, exposure to antibiotics, and bacterial diversity in the infant gut.

“This is the first study that we know of to show specific types of gut fungi play a role in weight gain and growth in early childhood,” says study co-first author Emily Mercer, a PhD candidate in ����������ٲ�’s research group in the (ACHRI) and the at CSM.

“Our findings suggest gut fungi may have important influences on early childhood development, highlighting the need for more research focused on the role of gut fungi in human health during the first years of life,” Mercer says.

Arrieta says the observational study, which involved a small cohort of 100 infants, wasn’t designed to — and did not — show a cause-and-effect relationship between infant gut fungal diversity and a child’s risk of becoming overweight or obese.

“This study sheds new light on some of the factors in the infant microbiome that influence a child’s metabolic health,” Arrieta explains. “It’s important that we don’t look at this huge ecosystem of microbes as a bacteria-only ecosystem.” 

“It is still too early for the study’s findings to be translated into health-care recommendations,” says study co-first author Mackenzie Gutierrez, a PhD candidate in ����������ٲ�’s research group.

“It will be important for our findings to be explored in other infant cohort studies in other locations around the world, to determine if these findings were specific to our cohort or if they are consistent in other populations as well,” Gutierrez says.

The study, “,” is published in the journal Cell Reports Medicine.

New study made possible by massive CHILD Cohort Study

����������ٲ�’s research focuses on the role of intestinal microbiota in paediatric health and disease. She is the co-author of Let Them Eat Dirt, a book for parents that explores how the microbiome influences childhood development and health.

Arrieta says the new study wouldn’t have been possible without a massive database collected by the , one of the largest multidisciplinary, longitudinal, population-based birth cohort studies in Canada. Started in 2008, the CHILD (Canadian Healthy Infant Longitudinal Development) study tracks factors critical to the health and development of more than 3,400 Canadian children. Researchers are actively following the study participants over time as they grow and develop — from mid-pregnancy into childhood and adolescence.

����������ٲ�’s used a series of infant samples from the CHILD study to look at how the microbiome develops and matures in the first five years of life. Mercer, a microbial ecologist, suggested the team compare each child to themself, rather than only compare groups as is typically done in clinical studies.

Gutierrez employed the statistical tools to compare changes in the fungal species in the infant gut to BMI and other factors, and tease out how all the factors were related.

“This large community of trillions of microbes truly has an influence on our development, but it’s complex,” Arrieta says. Her research group is now working on rodent-based experimental models of obesity, to explore the causal link between changing patterns of fungal diversity in the gut and early-life body weight.

Arrieta, a microbiologist by training and also a mother, was pregnant when she began her research, so she was personally interested in exploring the microbiome’s impact in early childhood.

“The message, building from all this new science about the microbiome, is that there’s a period that happens only early in life, during which the microbiome has a tremendous influence on the way our body develops,” she says. “We definitely need to pay attention to what happens to the microbiome early in life.”