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TMAO and Fish: The Data Is In For a Heart Unfriendly Metabolite

By June 21, 2024Kahn Longevity Center
TMAO and fish
Back in 2018, I appeared on the Joe Rogan Podcast (Episode 1175) and spent nearly 4 hours debating nutrition with Chris Kresser. He brought up some data that fish have TMAO in them, fish are considered heart healthy (debatable), and therefore plant diets are not the best choice. There was very little data in 2018 to make decisions on this point. I do not eat fish but Valter Longo, Ph.D. does included them twice a week in his Longevity Diet.

Now there are new data published from the Cleveland Clinic.

As background, some species of fish and seafood are high in trimethylamine N-oxide (TMAO), which accumulates in muscle where it protects against pressure and cold. Trimethylamine (TMA), the metabolic precursor to TMAO, is formed in fish during bacterial spoilage. Fish intake is promoted for its potential cardioprotective effects. However, numerous studies show TMAO has pro-atherothrombotic properties.

For the first time, the effects of fish or seafood consumption on circulating TMAO levels in participants with normal renal function were determined.


TMAO and omega-3 fatty acid content were quantified across multiple different fish or seafood species by mass spectrometry. Healthy volunteers (n=50) were recruited for three studies. Participants in the first study consented to 5 consecutive weekly blood draws and provided dietary recall for the 24 hours preceding each draw. In the second study, TMAO levels were determined following defined low- and high-TMAO diets. Finally, participants consumed test meals containing shrimp, tuna, fish sticks, salmon or cod. Blood TMAO levels were quantified by mass spectrometry in blood collected before and after dietary challenge.


TMAO+TMA content varied widely across fish and seafood species. Consumption of fish sticks, cod, and to lesser extent, salmon, lead to significant increases in circulating TMAO levels. Within one day, circulating TMAO concentrations in all participants returned to baseline levels.


The authors concluded that “some fish and seafood contain high levels of TMAO, and may induce a transient elevation in TMAO levels in some individuals. Selection of low TMAO-content fish is prudent for subjects with elevated TMAO, or impaired renal function”.

I do not eat fish. If you do eat fish and have heart disease, I would avoid fish with high TMAO content as TMAO has been shown to promote atherosclerosis, platelet aggregation (clumping and clotting), and perhaps, scarring of the heart and kidneys.