Carnitine, Choline, TMA, TMAO

All animal produce has comparatively high levels of carnitine and choline, which are a preferred food source for microbiome Firmicutes.

This increases ratio of firmicute:bacteroides, and F convert c and c to TMA which is absorbed, taken to liver to be converted to less toxic TMAO (though still toxic). can be measured in urine.

TMAO implicated in atherogenesis and various cancers.  (trimethylamine oxide)

Therefore, animal produce intake does not have a direct dose-response association with TMAO levels.
Levels are dependent on an elevated ratio of Firmicutes:Bacteroides

A habitual vegan can eat red meat "daily" and not get a rise in TMAO for about 5-14 days, the time taken for the F:B ratio to elevate.

Recall that microbiota split every 20 minutes.

Choline uptake by cancer cells is high, and cancer spread can be mapped by choline distribution in the body. 

Stanley Hazen, Cleveland Clinic  :  TMAO researcher.
Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis