Almost 180 million children across the world have stunted growth, a result of severe malnutrition and recurring childhood infection. Diminutive stature puts children at risk for cognitive impairment and further contraction of illness.
Recently, a study in the scientific journal Cell identifies a potential influence on one’s growth: gut microbiota. Microbiota are microorganisms or microbes that inhabit a particular environment, especially within the human body. The study, conducted by William Petri, a University of Virginia at Charlottesville professor, was driven by an inability to reverse malnutrition of Bangladesh infants despite the use of ostensibly effective dietary supplements.
To test the microbiome’s role in growth, the researchers inoculated mice with two different kinds of microbiota. One group of mice — “germ-free mice” who did not have a microbiota of their own at the outset of the experiment — were inoculated with “immature” microbiomes of children who exhibited symptoms of malnutrition. In addition, another set of mice were given “mature” microbiomes of healthy children. Results indicated that mice with the “mature” microbiomes put on more weight and developed denser bone mass.
In addition, working off of Petri’s work, François Leulier, a biologist from the École Normale Supérieure de Lyon in France, recognized another mechanism within growth stimulation: the microbiota’s influence on hormone activation.
According to the study, in normal organisms, growth hormones stimulate the production of a second hormone, insulinlike growth factor 1 (IGF-1). This second hormone then goes on to promote tissue growth. Although “germ-free mice” and “mature” mice each possessed the similar levels of IGF-1, the activation of the hormone differed. Although the mechanism in which microbiota activate IGF-1 is unclear, the researchers found that when the “germ free mice” were given more of the activated hormone, their tissue and bone growth were equivalent to that of the “mature” mice.
Finally, a separate group of researchers headed by Jeffrey Gordon, a microbiologist at Washington University in St. Louis in Missouri, hoped to examine why some mice have mature microbiomes while others do not. In the study, Gordon reveals how breast-feeding may help establish a healthy microbiome and influence the growth of organisms. “Healthy” mothers produce sugar molecules called sialylated human milk oligosaccharides. While babies do not actually utilize these molecules, gut microbiota “thrive on them,” according to the study. Moreover, mothers who are malnourished make less of the microbiota “food” and therefore influence the status of their child’s microbiome. When researchers added oligosaccharides to the diets of malnourished mice, the mice grew more muscle and bone mass in addition to increased brain and liver metabolism. The researchers believe that upon receiving the oligosaccharides, the “bacteria may in turn produce molecular building blocks to help the host’s body grow well.”
Although the correlation is exciting, the relationship between one’s microbiota and their level of growth and development is not fully confirmed. Furthermore, the success of the mice studies may not yield the same results for experiments on humans. Researchers also must be wary of how giving people new microbiota may influence other conditions such as obesity.
Nonetheless, as stated by Petri, the results “are a watershed moment in global health generally, and in nutrition specifically.” Further research into the relationship will yield ever-greater curiosity about the seemingly unlimited influence of the human microbiota.
By Josh Metzger ’17