When people think about malnutrition, they often think that not eating enough food leads to stunted growth, neurocognitive issues, weakened immune systems, and other health problems associated with malnutrition. While this is largely true, food scarcity and insecurity does lead to undernutrition, it is not the sole contributing factor to this pervasive global health problem. Jeffrey Gordon and his group at Washington University School of Medicine in St. Louis have shown once again that gut microbes play an important role in undernutrition in a paper in Science Translational Medicine.

To show the importance of the microbiome in undernutrition, Gordon’s team studied children in Malawi who were undernourished and others that were not. Specifically, they studied individuals with kwashiorkor, a form of severe undernutrition that occurs in children who often eat similar diets as other healthy children. They studied identical twins, one with the disease and one without the disease and sampled their gut microbes. They transplanted the bacteria from the sick child into germ-free mice to see what effects the bacteria would have. When transplanted into the mice, the bacteria were very harmful causing weight loss as well as severe damage to the lining of the intestines and colon.

The scientists looked for bacteria that were targeted by an important molecule of the immune system called immunoglobin A (IgA). IgA is prevalent throughout the body and specifically in the gut. It plays an important role in preventing the bacteria in the gut from interacting with the human cells that line our intestines. As we saw in the paper on the blog on Monday about emulsifiers in our food, when gut bacteria in the gut interacts with the epithelial cells of the gut lining, severe health problems can arise. The scientists found that IgA and the immune system largely targeted Enterobacteriaceae, a large family of bacteria found in the gut that includes E. coli, Salmonella, and many others. The scientists were able to prevent weight loss in the mice by transplanting two strains of IgA targeted bacteria from the guts of healthy children into the mice, before they were exposed to the bacteria from the undernourished child.

This is an important study as it not only shows the significant role that gut bacteria have on malnutrition, but it shows that it may be possible to use the microbiome as a diagnostic tool to identify which children are at risk for undernutrition, and it may also be a therapeutic target for intervention. The scientists also studied 19 other groups of twins and found that higher levels of Enterobacteriaceae led to a greater risk of kwashiorkor. By sampling children at a very early age for gut bacteria, it could be possible to identify which children were at greater risk of becoming malnourished and intervening with probiotics or other therapeutic foods to alter the microbiome.