Assessment and characterization of gut microbiota has become a major research area in human disease, including type 2 diabetes, the most prevalent endocrine disease worldwide. To carry out analysis on gut microbial content in patients with type 2 diabetes, we developed a protocol for a metagenome-wide association study (MGWAS) and undertook a two-stage MGWAS based on deep shotgun sequencing of the gut microbial DNA from 345 Chinese individuals. We identified and validated approximately 60,000 type-2-diabetes-associated markers and established the concept of a metagenomic linkage group, enabling taxonomic species-level analyses. MGWAS analysis showed that patients with type 2 diabetes were characterized by a moderate degree of gut microbial dysbiosis, a decrease in the abundance of some universal butyrate-producing bacteria and an increase in various opportunistic pathogens, as well as an enrichment of other microbial functions conferring sulphate reduction and oxidative stress resistance. An analysis of 23 additional individuals demonstrated that these gut microbial markers might be useful for classifying type 2 diabetes.Seems pretty reasonable. All they say there is that they found associations between bacteria and diabetes. That is interesting but they do not seem to present any evidence about a causal connection. Perhaps people who get type II diabetes end up then having their microbiome shift. Perhaps a shift in the microbiome causes type II diabetes. Or perhaps something else (e.g., excessive inflammation) causes both type II diabetes and microbiome shifts. Who knows.
But alas a bit of hype crept into some of the the news stories. And it seems that the scientists behind the study are responsible for some of this hype. For example, consider the article Changes in Intestinal Bacteria Linked to Type 2 Diabetes - US News and World Report. One quote is a bit much for me:
"I think our study provides many targets for disease prevention and treatment through gut microbiotia in the near future," said study senior author Jun Wang, executive director of the Beijing Genomics Institute in Shenzhen, China.Fortunately the reporter who wrote this story does a very good job of providing cautious interpretations. See for example:
"There's no way right now that you can say there's a cause-and-effect relationship. It could be that the patients with diabetes were treated with drugs that changed their gut flora. Or maybe they ate differently? This is an interesting hypothesis -- that gut bugs could influence diseases states -- but it's far from proven," said Dr. Stuart Weinerman, associate chief of the division of endocrinology at North Shore University Hospital/Long Island Jewish Medical Center in New Hyde Park, N.Y.Also see stories like Gut bacteria could cause diabetes from Science Codex. The title alone makes me want to cry. Some quotes as well as discussion in that article also seem, well, not cautious enough.
The research, which was recently published in the scientific journal Nature, also demonstrated that people with type 2 diabetes have a more hostile bacterial environment in their intestines, which can increase resistance to different medicines.Definitely not buying this "hostile" environment claim. Fortunately as with the US News story, there is some caution presented
"It is important to point out that our discovery demonstrates a correlation. The big question now is whether the changes in gut bacteria can affect the development of type 2 diabetes or whether the changes simply reflect that the person is suffering from type 2 diabetes."So - the stories seem to actually be doing an OK job with the correlation vs. causation issue I have complained about many times. And though some of the scientists may be pushing a bit of overinterpretation the reporters and even the press releases have some decent cautionary statements.