Mixed
Chronic dietary l-carnitine supplementation induces gut microbiota to convert l-carnitine into trimethylamine N-oxide (TMAO), an atherogenic metabolite, via a two-step microbial pathway involving gamma-butyrobetaine (γBB).
If you eat red meat regularly, adding l-carnitine supplements may increase your levels of TMAO, a compound linked to heart disease risk. Vegans and vegetarians generally do not produce significant TMAO from l-carnitine unless they supplement chronically. If you are an omnivore, avoid l-carnitine supplements unless prescribed, as they may promote atherosclerosis pathways.
In humans, dietary l-carnitine is converted into the atherosclerosis- and thrombosis-promoting metabolite TMAO via 2 sequential gut microbiota–dependent transformations: (a) initial rapid generation of the atherogenic intermediate γBB, followed by (b) transformation into TMA via low-abundance microbiota in omnivores, and to a markedly lower extent, in vegans/vegetarians. Gut microbiota γBB→TMA/TMAO transformation is induced by omnivorous dietary patterns and chronic l-carnitine exposure.
Why this rating
High-quality human clinical trials with isotope tracers and controlled diets, though observational associations for CVD are noted.
Source
l-Carnitine in omnivorous diets induces an atherogenic gut microbial pathway in humans
Robert Koeth et al. · Journal of Clinical Investigation · 2018
DOI 10.1172/jci94601
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