Patrick Guilfoile: Microbes and malnutrition?
Severe malnutrition is a leading cause of death of children in less developed countries. One form of malnutrition is kwashiorkor. If you’ve seen pictures of a listless child with spindly arms and legs, protruding ribs and a very distended belly, you’ve seen a person with this disease.
A poor diet is a key factor that leads to kwashiorkor. However, the fact that some children eating the same foods in the same households develop the condition, and some don’t, suggest that diet is not the only factor leading to this form of malnutrition.
In a recent report, scientists from Malawi and the United States shed some new light on kwashiorkor. These researchers studied more than 300 pairs of Malawian twins during the first three years of their lives. They were particularly interested in the 43 percent of the twin pairs where one twin had kwashiorkor and the other was well-nourished. Suspecting that there might be a connection between the intestinal flora and malnutrition, these scientists studied the gut microbes of these pairs of children (through analysis of fecal samples). They found dramatic differences in the microbial flora in even identical twins who ate the same foods but one twin was malnourished and the other was well nourished.
One of the challenges, though, in research (and life in general) is differentiating between a correlation and a causal effect. Often, we are interested in determining whether one thing causes another. In many cases, though, the best we can do is to say two things are associated (correlated) and one may or may not cause the other thing to happen. That is where the scientists were at this point in the study. There was a correlation between under-nutrition and the gut microbes of these children, but it could be that a deficient diet triggered the formation of different microbial communities, and the microbes were simply a passive reporter of poor nutritional status.
So the scientists moved to studies in animals. They either fed germ-free mice the gut microbes from malnourished or well nourished twins. They found that the mice which had received the "malnourished" microbes, if fed a diet these children normally ate, began losing weight. On the other hand, mice who received the "well nourished" microbes did not lose as much weight on a Malawian diet. Mice that were fed normal mouse chow, or another nutritional food, regardless of the microbes they harbored, gained weight. These experiments showed that the microbes did have a causal effect in the development of kwashiorkor. The scientists did further experiments that determined that some of the microbes from malnourished children produced chemicals that irritated the intestines, likely reducing the uptake of nutrients. In addition, it appeared these microbes also poisoned the chemical factories in intestinal cells, preventing the extraction of much of the energy in food, further strengthening the causal link between these microbes and malnutrition
One unanswered question in the study is what caused the differences in nutritional status of some of these pairs of twins. It is speculation, but one possibility is an earlier gastrointestinal infection that deranged the microbial flora in the digestive system of one twin but didn’t affect the other twin. Once these harmful microbes were established, they stayed in place, leading to kwashiorkor. It now appears that malnutrition involves not only our diet, but also the microbes we harbor and what they do when they share our meals.
More information is available in "Gut Microbiomes of Malawian Twin Pairs Discordant for Kwashiorkor" Science 339:548-554, Feb. 1, 2013.
PATRICK GUILFOILE has a Ph.D. in bacteriology and is currently an interim associate vice president at Bemidji State University.