Why Do Binders Help? Bile Acid Malabsorption as a Missed Diagnosis in Damp-Building Illness

Background: Exposure to damp and water-damaged buildings is associated with well-established respiratory and allergic health effects, and exposed individuals frequently report symptoms across multiple additional systems. Illness persisting after such exposure is widely attributed to retained mycotoxins and treated with oral binders. Urine mycotoxin panels, routinely ordered in functional and integrative practice to support that attribution, cannot distinguish building exposure from ordinary dietary intake. The clinical response to binders, meanwhile, has never been controlled for the bile acid-modulating properties those agents share. Hypothesis: Bile acid malabsorption (BAM) — identified in 28.1% of patients meeting criteria for diarrhea-predominant irritable bowel syndrome (IBS-D) at a seven-day SeHCAT retention threshold below 10%, independently corroborated at 30% by a second meta-analysis at the same threshold, and substantially underdiagnosed in the United States — may explain a clinically important subset of binder responses in this population, particularly among patients with chronic diarrhea following damp-building exposure. The argument advanced here does not require that damp-building exposure cause BAM. It requires only that BAM be present in this population at the base rate observed in any group selected for chronic diarrhea, that it go unscreened, and that agents which treat it be prescribed under a different rationale. Multiple binder types used in this population — including bile acid sequestrants, activated charcoal, and probiotics — share documented bile acid-modulating properties. What has been interpreted as “biotoxin binding” may be substantially or entirely explained by bile acid sequestration and modulation of the bile acid pool. Implications: If confirmed, this hypothesis would redirect clinical attention from unvalidated mycotoxin testing toward a diagnosable, treatable gastrointestinal condition. It would also offer a parsimonious explanation for treatment response patterns — including rapid onset and variable efficacy — that the mycotoxin-binding model does not adequately explain; the discontinuation-relapse pattern sometimes cited for this population is more equivocal, for reasons discussed in Section 7.