Why Dysbiosis, SIBO, Hydrogen Sulfide Intolerance, MCAS, and Long COVID May All Be Downstream of a Single Event — The distinction nobody makes: butyrate production vs. butyrate utilization

Now we can state one of the most important and most overlooked ideas in this entire field. Low butyrate on a stool test and an inability to use butyrate are two completely different problems, and they require opposite interpretations. A stool report can show low butyrate for the obvious reason: production is low because the butyrate-producing bacteria are depleted. That's a supply problem, and the instinct to feed fiber and reseed Clostridia makes sense. But in many complex cases, butyrate is present — sometimes even abundant — and the colonocyte still can't use it. The supply is fine. The utilization is broken. The cell lacks the mitochondrial capacity, the redox balance, the intact iron-sulfur clusters, the functioning NAD/FAD machinery, or the electron transport competence to actually oxidize the butyrate sitting right in front of it. This is why some people feel worse on butyrate supplements, on fiber, on the exact interventions that are supposed to help. Pushing more substrate into a cell that can't process it is like flooding the carburetor of a car whose engine won't turn over. (And there is real biology here — Donohoe and colleagues showed butyrate is the colonocyte's energy substrate, and when it can't be oxidized, it accumulates and changes the cell's behavior entirely.) If you only read stool butyrate, you cannot tell these two patients apart. One needs more butyrate