Eggs are a daily staple across most of Asia: in congee, braised dishes, steamed custard, or just boiled and eaten with rice. In recent years, some articles have warned that eggs might harm your heart through something called TMAO. The concern is real enough to explain, but the research on people eating eggs is more reassuring than those headlines make it sound.
Your gut bacteria turn egg yolk into something your liver processes
Inside your digestive system, trillions of bacteria break down your food. This community of bacteria is called your gut microbiome, and it varies from person to person, in ways our piece on gut microbiome and type 2 diabetes looks at from a different angle. Egg yolks are rich in a nutrient called choline, which your body needs for brain function, liver health, and building cells. When choline reaches your gut, certain bacteria can break it down into a compound called trimethylamine, or TMA. Your liver then converts TMA into TMAO. At high levels in your blood, TMAO appears to promote fatty buildup inside blood vessels, raising the risk of heart attack and stroke.[1]
What high TMAO does inside a blood vessel
Low TMAO
Vessel walls stay clear. Blood flows freely.High TMAO over time
Fatty deposits build up on vessel walls, blood flow narrows, and heart risk rises.When researchers fed people eggs, something different happened
A proper clinical trial gave overweight women two eggs a day and measured their blood TMAO before and after. Choline levels rose as expected. TMAO levels did not change.[2] Another trial compared eating whole eggs against taking a choline supplement with the exact same amount of choline. The supplement raised TMAO. The eggs did not, and the egg group also had lower inflammation markers.[3] The pathway above suggests eggs should raise TMAO. In practice, they mostly do not. The reason comes down to who is eating them.
Why the same egg affects two people differently
Only certain gut bacteria carry the ability to convert choline into TMA, and not everyone has large numbers of those bacteria.[4] Two people can eat the same breakfast of two eggs and end up with very different results. Someone with few TMA-producing bacteria lets most of the choline pass through largely unchanged, so their liver receives little TMA to convert and their TMAO stays low. Someone with many TMA-producing bacteria converts a much larger share of that same choline into TMA, and their liver ends up processing a heavier load, which can push TMAO five times higher from the identical meal. Egg studies produce conflicting results because the egg is not the only variable; the person eating it matters just as much.
One group shows a different picture. People who already have metabolic syndrome, a combination of high blood sugar, high blood pressure, and excess belly fat, showed a trend toward higher TMAO after eating eggs and meat, alongside gut bacteria patterns already linked to inflammation before the meal.[5] The same overlap between gut bacteria and metabolic conditions shows up in our coverage of PCOS and your gut. If metabolic syndrome applies to you, raise it with your doctor rather than using the general population data to guide your decision.
What eggs bring to the table
Eggs are one of the most complete protein sources available, along with vitamin D, B vitamins, and antioxidants linked to eye health. They have almost no fiber, so pairing them with vegetables, brown rice, or beans, or with fermented sides like the ones covered in miso and your gut, covers the one gap they have.
Easy pairings that add fiber
- Congee with leafy greens
- Stir-fried vegetables on the side
- Brown rice or oats
- Beans or lentils at the same meal
Talk to your doctor if
- You have metabolic syndrome or type 2 diabetes
- You eat eggs multiple times a day, every day
- You have a family history of early heart disease
The bottom line
For most people eating eggs a few times a week, whether boiled, steamed, braised, or in congee, the TMAO risk does not appear to be a concern based on current clinical evidence. The pathway from egg yolk to heart risk is real, but eating eggs does not automatically trigger it. Your gut bacteria determine far more of that outcome than the egg itself does.
Sources
This content is for educational purposes only and is not a substitute for professional medical advice.
- Metware Bio, "Trimethylamine N-oxide (TMAO): From Gut Microbiome Pathway to Cardiometabolic Risk"
- Journal of Nutrition, "Whole egg consumption increases plasma choline and betaine without affecting TMAO levels or gut microbiome in overweight postmenopausal women"
- Nutrients, "Comparison between Egg Intake versus Choline Supplementation on Gut Microbiota and Plasma Carotenoids in Subjects with Metabolic Syndrome"
- Gut Microbes, "Urinary TMAO Levels Are Associated with the Taxonomic Composition of the Gut Microbiota and with the Choline TMA-Lyase Gene (cutC)"
- Molecular Nutrition & Food Research, "Plasma and Urinary TMAO and Methylamine Responses to Meat and Egg Ingestion"
