Bacteria in Infants' Guts—& Their Antibiotic Use—Could Be Making Kids Chubbier

Overweight kids often become overweight adults. New research suggests a couple reasons why and suggested that there may be ways to intercept that fate.

The research was published online in the journal Microbiome by a team from the University of Helsinki, Helsinki University Central Hospital, and Radboud University Nijmegen. They compared the gut bacterial microbiome present in three-month-old infants with their body mass later as kids of five to six years old—and looked to see if whether antibiotic treatments they had during that time influenced the association.

The gut bacteria—analyzed in the stool of the children when they were three months old—fell mostly into two phylums: Actinobacteria, with most of these belonging to the Bifidobacterium family, and Firmicutes, mostly from the Streptococcus family.

Bacteria in Infants' Guts—& Their Antibiotic Use—Could Be Making Kids Chubbier — Bifidobacteria. *Image by Y tambe/Wikimedia Commons*

There were 162 children in the study, and as five and six year olds, their weights were mostly in the normal body mass range with a body mass index (BMI) less than seventeen. Some of the children were overweight (BMI >17) and some were underweight (BMI <14).

The amount of the bacteria in the kids' guts fell along lines correlating with the kids' body mass, but the correlations were different for the different bacteria.

Increasing amounts of streptococci present in the infants' guts corresponded to increases in BMI of the children at age five to six. The reverse was true for bifidobacteria—increasing amounts of bifidobacteria present in the infants' guts corresponded to decreases in BMI of the children at age five to six.

Children with increases in any kind of Firmicutes, including Streptococcus, in their stool as infants, who also had several courses of antibiotics since birth, had an even stronger association with increases in BMI than those who took only minimal antibiotics over their lifetime.

Healthy Guts & Antibiotics

Once thought to be the source of bacterial colonization of an infant's gut, the intrauterine environment has been determined not to be the main source of those bacteria.

While a mother's womb does contain some bacteria, the source of bacteria that develop in an infant's gut is now known to be acquired after birth and come from the mother's vaginal, gastrointestinal, and skin bacteria. Our gut microbiome changes quickly and often after birth, affected by diet, antibiotics, and exposure to other microbes. Check out the video below for a quick overview of the microbiome:

A previous study from 2015 comparing the intestinal microbiomes of healthy children and adults showed that the children's guts were enriched in Bifidobacterium, Faecalibacterium, and Lachnospiraceae-type bacteria, while adults had greater numbers of Bacteroides bacteria in their gut.

Gut bacteria can affect digestive, metabolic, and immune health, and there is increasing scientific evidence that bifidobacteria in particular, plays a role in energy metabolism.

Other studies have shown that two different kinds of bifidobacteria reduced weight gain in rodents fed a high fat diet. Some types of gut bacteria release toxins that are absorbed into the blood and cause inflammation that changes the body's metabolism of fats. Bifidobacteria may inhibit that process, allowing for better fat metabolism.

The study from Helsinki and Nijmegen did not show that the bacteria or the antibiotic treatments caused the increase or decrease in BMI of the children, but it did show strong correlations between the two.

How early and changing gut microbiomes can influence later health is the subject of ongoing research. For now, these correlations can at least serve as indicators of later obesity risk. The idea that courses of antibiotics in infancy and early childhood could impact later weight is an increasingly important research finding. These observations will provide avenues for future scientific research and possible candidates for influencing future weight by modifying the gut microbiome, or by judicious use of antibiotics in early childhood.