One of the prime suspects here runs into an extremely influential entrenched forces with an interesting against this sort of work. For instance nearly all foods

One of the prime suspects here runs into an extremely influential entrenched forces with an interesting against this sort of work. For instance nearly all foodstuffs of various sorts in the US today are treated with glyphosate both as an herbicide and as a crop desiccant. On the latter part even various cereals and wheats are generally treated with glyphosate just before harvest to work as a dessicant, or drying agent (which, as an aside, is where the hypothesis that 'gluten sensitivity' is actually a response to glyphosate comes from). The most important point here is that while the impact of such is debate, it is not debated that glyphosate has a substantial and not entirely clear impact on gut bacteria. Monsanto reacts extremely aggressively against any publication, from anybody, suggesting any potential issue with their products. For instance when the World Health Organization indicated that glyphosate is a probable carcinogen, even they came under sustained aggressive assaults from Monsanto's PR and 'approved science' machine. That sort of pressure is something that, if you're a researcher who's not ideologically driven, is going to work as a major deterrent. And of course it's entirely possible that glyphosate is not the cause here, but it's something that you presumably would want to extensively research first and foremost due to its ubiquitousness and interactions with gut flora, yet that's not really happening, on the scale it should be, outside of studies with major conflicts of interests. -------- EDIT: One quick addendum. The reason I jumped from analyzing gut bacteria in and of itself to examining outside players is because your gut biome is going to a product of environmental factors. So it's not so much the biome that matters as how we are changing it, unless you assume that there has been no real change in incidence rates over the decades but simply more widespread reporting - which is certainly possible and something that would also need to be investigated.