The problem is not obsession with the gut, but that the entire notion of gut microbiota is being misappropriated by snake oil salesmen and "alternative medicine

The problem is not obsession with the gut, but that the entire notion of gut microbiota is being misappropriated by snake oil salesmen and "alternative medicine" crazies while healthcare professionals continue to have zero incentive to keep up with new science or go above the usual "eh idk your basic bloodwork is fine, must be in your head", and people are clever enough to home in on there being something wrong, but not to be rational about it. As far as the science goes, probiotics have modest ability to improve gut biota and may sometimes worsen it, while the effects of diet are nearly strictly temporary despite rapid changes. The only thing that's been shown to reliably effect big, durable changes is Fecal Microbiota Transplantation - and even then, the response rate for most disorders is limited due to how entrenched the existing microbiome is and difficulty of transferring sensitive strains, especially for conditions like IBS that appear to often entail antibiotic-resistant biofilms. For a healthy microbiome, even sugar has minor effects unless consumed all day every day. Past that, there's science linking elevated gut bacteria toxins levels and antibodies with depression, fatigue, neurodegenerative disease, or demonstrating large influences of certain microbes or their metabolites on conditions like diabetes, ADHD, autism, hypertension, PCOS. Some conditions seem to be caused by other infections, like endometriosis(endometrial bacterial infiltration), UTIs in elderly, especially women, oral gingivitis bacteria contributing to Alzheimer's Disease and cardiovascular disease, or herpesviral (re)activation and AD and ME/CFS, though I suspect that may be secondary to other immune system activation. Also: Almost all diarrhea is caused either by C. Difficile or by deficiency of SCFA-producing microbes. The only way to get bloating is by bacterial fermentation of stuff that shouldn't be being fermented. And sure, changes in gut motility and physiological function affect that, but the microbiome has been demonstrated to be a significant predictor of all of it. Animal models replicate anorexia in mice using stool transplants from ill humans(Parkinson's, schizophrenia's neurological changes, too), gut dysbiosis predicts colorectal cancer, butyrate production predicts energy levels in healthy volunteers and disease severity in ME/CFS patients... and the list goes on and on and on. It's not the ONLY thing wrong with people, so many of us have undiagnosed breathing-related sleeping disorders - apnea is often scored using antiquated, insufficiently sensitive criteria, and many young people, especially women, wake up so fast and often that apneas/hypopneas barely happen, termed Upper Airway Resistance Syndrome. Urogenital dysfunction seems typically related to pelvic floor function and posture&breathing. ME/CFS often persists after a single viral trigger, and Long COVID can be just as bad. But overall? Yeah, almost everything links back to inflammation, and usually the gut, to a point that makes treating everything as a mental disorder and psychiatry look as barbaric as their origins in mental asylums and lobotomies.