A study by Ryan Newton and colleagues in mBio, the open access journal of the American Society for Microbiology, found that the bacterial composition of city sewage can almost precisely predict obesity rates in that city.
The researchers studied the microbial community of sewage from 71 US cities from 31 states using high-througput 165 rRNA gene sequencing technology.
Although on average only 15% of bacterial sequences in each sample represented bacteria known to occur in human stool, they were able to capture most (97%) of human fecal oligotypes.
Based on the distribution of three primary oligotypes representing different proportions of Bacteroidaceae, Prevotellaceae, or Lachnospiraceae/Ruminococcaceae, the researchers were able to predict whether samples came for cities with high or low prevalence of obesity with 81-89% accuracy.
No such relationship was found with non-fecal oligotypes, suggesting that this relationship was indeed due to the representation of human fecal bacteria in the sewage samples.
Obviously, it is very possible that the sewage bacterial composition reflects “lifestyles” associated with obesity rather than actual body weights, but the very fact that it was possible to identify important predictive differences in bacterial patterns between cities with varying obesity rates, together with the increasing recognition that gut bacteria may well play a role in obesity (and other metabolic diseases), is fascinating enough.
Should these findings be reproducible across other populations, I can only wonder whether sewage sampling may one day serve as a simple way to study changes in nutrition and obesity rates in whole populations.
Indeed, I can picture future public health scientists poring over sewage data to check if their public health policies to reduce obesity are in fact working.