The same way you support any causal claim, by controlling for confounders. What gives you so much confidence that a suboptimal microbiome is tautologically acco

The same way you support any causal claim, by controlling for confounders. What gives you so much confidence that a suboptimal microbiome is tautologically accompanied by "nasty and humiliating" IBS symptoms, to the degree that would cause depression? Are you under the impression that everyone with a measurably poor microbiome automatically has nasty and humiliating IBS symptoms? You can assume that everyone involved in performing, analyzing, and reporting the study is incompetent, but at that point why not just assume that the entire article is inaccurate and that one can never understand anything about the world? I'm the last person to slavishly believe scientific authorities' interpretation of evidence when it's clearly done poorly (see: all of Covid). But it's bizarre to claim that researchers wouldn't have thought to rule out the most basic alternate hypotheses, especially when they have the data to do so.