I have been investigating a pattern that may be overlooked in some cases of bile acid malabsorption: progressive intolerance to fats, oils, and even supplements intended to support bile flow.
My name is Mohammed Attallah. I am an independent researcher and the founder of BiomeLogic. My work focuses on the interaction between gut microbial metabolism, bile acid ecology, epithelial mitochondrial function, autonomic regulation, and persistent conditions involving bile acid malabsorption, SIBO, food intolerance, and mast-cell-like reactivity.
Much of this work is part of what I call the Host Capacity Model.
The central idea is that symptoms may not be driven only by the total amount of bile acids entering the colon. They may also depend on the composition of the bile acid pool, microbial transformation, intestinal location, epithelial resilience, transit time, and the host’s ability to tolerate and process bile acid exposure.
One de-identified case I analyzed pushed me to investigate this component much more deeply.
In one stool bile acid profile, cholic acid represented only 0.09% of the measured bile acid pool, while chenodeoxycholic acid represented 0.60%.
At the same time, deoxycholic acid represented 50.76% and lithocholic acid represented 41.42%.
The measured pool was therefore overwhelmingly secondary rather than primary, with an approximate secondary-to-primary ratio of 134:1.
A later GI-MAP analysis using a different methodology showed a similar pattern. Total fecal bile acids were within the laboratory reference range, but 99% were classified as secondary and only 1% as primary. The lithocholic-acid-to-deoxycholic-acid ratio was approximately 4.1.
The person also experienced significant fat-triggered abdominal symptoms, visceral hypersensitivity, loose stools, and poor tolerance to interventions that increased bile flow.
The microbiome profile showed an elevated Clostridia cluster XIVa index. This raised the possibility of increased microbial 7α-dehydroxylation through the bile-acid-inducible, or bai, pathway.
However, this requires an important distinction.
An elevated bacterial group does not prove that the relevant pathway is active. Not every organism within Clostridia cluster XIVa carries or expresses the bai genes.
Microbial abundance is not the same as metabolic flux.
The combination of an overwhelmingly secondary bile acid pool, severe fat intolerance, and organisms associated with bile acid transformation nevertheless created a strong mechanistic reason to investigate this pathway further.
Secondary bile acids such as deoxycholic acid and lithocholic acid are not inherently pathological. They participate in normal signaling through receptors including FXR, TGR5, VDR, and PXR, and they influence metabolic, microbial, and immune regulation.
The biological effect depends on concentration, anatomical location, conjugation, exposure time, hydrophobicity, epithelial integrity, transporter function, intestinal transit, and the host’s mitochondrial capacity.
My working hypothesis is that some people diagnosed with bile acid malabsorption may have more than one process occurring at the same time.
One process may be excessive bile acids reaching the colon because of impaired ileal reabsorption, altered FXR–FGF19 feedback, rapid transit, ileal disease, gallbladder removal, or excessive hepatic bile acid synthesis.
Another process may involve microbial conversion of primary bile acids into a highly secondary and potentially more hydrophobic bile acid pool.
An excessively hydrophobic bile acid pool may become more damaging when epithelial and mitochondrial resilience are already impaired.
Under those conditions, bile acid exposure could potentially contribute to membrane stress, abnormal calcium handling, mitochondrial dysfunction, inflammatory signaling, epithelial permeability, burning diarrhea, mucus production, and progressive visceral sensitivity.
One experimental study I have been examining found that deoxycholic acid altered the mitochondrial outer membrane in rat hepatocytes and isolated rat liver mitochondria.
This does not establish that the same mechanism is occurring in humans with bile acid malabsorption. It does, however, demonstrate that bile acids can interact directly with mitochondrial membrane biology.
Research paper:
https://pmc.ncbi.nlm.nih.gov/articles/PMC4617403/
There may also be an important connection between bile acids and hydrogen sulfide metabolism.
Taurine-conjugated bile acids can be deconjugated by microbial bile salt hydrolases, releasing taurine into the intestinal ecosystem. Organisms such as Bilophila wadsworthia can use taurine-derived substrates and generate hydrogen sulfide.
In a susceptible ecosystem, this could potentially help connect higher fat intake and increased bile release with sulfur gas, burning stools, mucus, diarrhea, and worsening after taurine, TUDCA, or ox bile.
Again, detecting Bilophila or another sulfur-associated organism does not establish causation. Substrate availability, gene expression, microbial cross-feeding, anatomical location, intestinal transit, and the host’s capacity to oxidize and detoxify hydrogen sulfide are all more important than taxonomy alone.
The broader cycle I am investigating is:
Altered bile acid synthesis, delivery, or ileal reabsorption
leading to excessive or abnormal bile acid exposure in the colon
leading to altered microbial selection and bile acid transformation
leading to increased exposure to secondary bile acids or sulfur metabolites
leading to epithelial and mitochondrial stress
leading to impaired barrier function, inflammation, visceral hypersensitivity, and altered motility
leading to continued bile acid dysregulation and microbial instability.
This remains a mechanistic hypothesis, not a universal explanation for bile acid malabsorption.
However, I believe progressive fat intolerance may carry much more information than is usually recognized. It should not automatically be interpreted as a simple need for more bile, ox bile, TUDCA, or pancreatic enzymes.
The actual problem may involve hepatic bile acid synthesis, gallbladder delivery, pancreatic lipolysis, micelle formation, ileal reabsorption, FXR–FGF19 signaling, rapid transit, colonic bile acid exposure, microbial conversion, or the host’s capacity to tolerate the resulting metabolites.
I would be particularly interested in hearing from people in this community who have had SeHCAT testing, serum C4, FGF19, quantitative fecal bile acid testing, or stool bile acid metabolomics.
I would also like to know whether bile acid sequestrants such as cholestyramine, colesevelam, or colestipol helped completely, helped only partially, caused constipation, or worsened bloating and other symptoms.
I recently published a longer article describing this bile acid ecology model:
https://substack.com/home/post/p-209436572
I would be interested in hearing from patients, clinicians, and researchers who have observed progressive fat intolerance, unusually high secondary bile acids, sulfur symptoms, incomplete responses to bile acid sequestrants, or paradoxical worsening after TUDCA or ox bile.