New Research on Eggs Plus Microbiome: No Heart Attack Risk, But Some Gut Bacteria Drive Inflammation

Sam Westreich, PhD

Does microbiome + eggs = heart attacks? The truth is a bit more complex
Her vision? Egg-celent.Hannah Tasker/Unsplash

Eggs are one of those foods that, like coffee, seem to flip back and forth on the “is it healthy” scale. They’re bad for you! No, they’re good for you! They increase risk of heart attacks because of high cholesterol! No, they’re fine for cholesterol!

Now, with more people focusing on the gut microbiome and its complex effects on our own health, eggs have come up… again. The newest question: do eggs interact with our gut microbiome to cause problems? Or are they still fine to eat?

The answer is more complex than it seems at first glance. It turns out:

  1. Eggs could be bad, based on their chemistry…
  2. …but they’re probably not, based on our anatomy…
  3. …but they still could be problematic for some people.

Let’s dig into this question, and get a clear answer in black and (egg) white.

From choline to TMAO

In order to understand the concerns with eggs, we need to understand the TMAO synthesis pathway. (Don’t worry — this explanation will remain high level and easy to follow!)

Our bodies can make a compound called trimethylamine-n-oxide, or TMAO for short. TMAO is bad news for us; it prevents our bodies from removing excess cholesterol from our arteries, increases the ability for platelets in our blood to stick together and form clots, and can trigger our immune system to overreact (also known as inflammation).

High TMAO is associated with heart attacks, stroke, and kidney disease. We want to avoid high TMAO levels.

But where does TMAO come from? It actually is produced by our gut microbiome, through a multi-step process beginning with two other inputs, either choline or carnitine. Both of these are nutrients that we eat normally in food.

So when we eat foods high in choline or carnitine, our gut microbes can convert these into a precursor called TMA, which then gets converted into TMAO.

We need some choline in our diet, but it sounds like we want to not overdo it, and avoid carnitine, in order to keep our TMAO levels (and heart attack/stroke chances) low.

But eggs are high in choline! In fact, 4 eggs gives you well over 100% of your daily choline needs. Does this mean high-choline eggs can lead to heart disease and should be avoided?

“Not so fast!” says Captain Anatomy

Before we cut eggs out of our diet, however, we need to consider our anatomy. Yes, gut microbes can convert choline and carnitine into TMAO. But do they actually get the chance to do so?

The answer, it turns out, is no — due to the way our anatomy is set up, and the specific type of choline in eggs.

Choline tends to come in two forms; it’s either bound to a phospholipid (a fat molecule), or it’s in a “salt” form, bound to tartaric acid.

  • When we take a choline supplement, or choline is added to a food or multivitamin, it tends to be in the “salt” form, as choline bitartrate.
  • In eggs and some other naturally choline-rich foods, however, it’s attached to that phospholipid, letting it be absorbed along with other fat.

The fat-soluble choline in eggs is very quickly absorbed by our body, in our small intestine. This choline never makes it to the gut microbes in our colon — so it’s never turned into TMAO.
This guy’s gonna get absorbed so fast, it’ll make your head spin.Photo by Ben Kolde/Unsplash

Hooray! This is good news for people who love big omelettes at breakfast; eggs may be full of choline, but it’s fat-bound choline that is quickly absorbed into the body for nutrition and never makes it through the digestive tract to the gut microbes that could convert it into troublesome TMAO.

Instead, more of the TMAO that ends up in our bloodstream comes from a different food, one that’s very well connected with heart disease: red meat. Red meat is high in carnitine, which also ends up getting converted into TMAO.

People trying to avoid heart disease or stroke, who are concerned about TMAO levels in their blood, will see more success by cutting out red meat from their diet, rather than targeting eggs for elimination.

So eggs are totally in the clear, gut microbiome-wise?

Not quite. We’ve eliminated choline concerns, but eggs also contain a lot of sulfur compounds. There are two proteins in eggs, globulin and keratin, that have sulfur bound in their structure; when the egg starts to break down, the sulfur is released, which is why most of us associate the smell of hydrogen sulfide (a stinky gas) with rotten eggs.

That release of hydrogen sulfide doesn’t just happen to an egg left out on the counter too long. It can also occur in our body, as some microbes will generate the gas as a byproduct of feasting on the sulfur-containing compounds in the eggs.

Hydrogen sulfide gas is not great for our insides. Along with making our farts very stinky, it can also trigger gut inflammation if present at high levels, as it damages the barrier that separates our gut microbes from the rest of our body cavity.

Not everyone will have hydrogen sulfide producing bacteria in their gut. (Remember, every person has a unique microbiome, which can mean that a treatment for one person may not work for another.) There are a number of different sulfide producing bacteria, if you’re interested: Deltaproteobacteria (mesophilic genera Desulfovibrio, Desulfobacterium, Desulfobacter, Desulfobulbus), Thermodesulfovibrio, Desulfotomaculum, and Archaeoglobus (Euryarchaeota).

For people with high levels of sulfide-producing bacteria, they can try introducing lactic-acid fermenting species to balance out the sulfur production, such as Lactobacillus (commonly found in yogurts or other fermented dairy), and they can also reduce their consumption of sulfur-rich foods, such as eggs.

In summary: eggs are fine for the heart, but can add excess sulfur

Eggs! Great in so many foods — and not nearly as bad for our heart as we once feared. Yes, eggs are high in choline, a compound which can get fermented by our gut bacteria into heart-damaging TMAO. But the choline in eggs is a rapidly absorbed form, so our body absorbs most of it before it can reach the gut bacteria in our colon. Absorbed before it can be converted into TMAO!

Eggs also contain a lot of sulfur-containing compounds, which can be digested by some microbes to cause hydrogen sulfide gas release. At low levels, hydrogen sulfide is fine, but high levels can trigger inflammation and colitis. People with intestinal inflammation may consider:

Overall, eggs can be a valuable component in a healthy diet, and they’re not likely to screw up our gut microbiome.

Disclaimer: this author is not performing any egg research, or getting any funding from the egg industry (Big Egg?).

Do you have any diet concerns when it comes to eating eggs?


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A microbiome scientist working at a tech startup in Silicon Valley, Sam Westreich provides insights into science and technology, exploring the strangest areas of biology, science, and biotechnology.

Mountain View, CA

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