What Explains the Egg-Cancer Connection

The reason egg consumption is associated with elevated cancer risk may be the TMAO, considered the “smoking gun” of microbiome-disease interactions.

“We are walking communities comprised not only of a Homo sapiens host, but also of trillions of symbiotic commensal microorganisms within the gut and on every other surface of our bodies.” There are more bacterial cells in our gut than there are human cells in our entire body. In fact, only about 10 percent of the DNA in our body is human. The rest is in our microbiome, the microbes with whom we share with the “walking community” we call our body. What do they do?

Our gut bacteria microbiota “serve as a filter for our largest environmental exposure—what we eat”—and, “technically speaking, food is a foreign object that we take into our bodies” by the pound every day. The “microbial community within each of us significantly influences how we experience a meal…Hence, our metabolism and absorption of food occurs through” this filter of bacteria.

However, as you can see at 1:22 in my video How Our Gut Bacteria Can Use Eggs to Accelerate Cancer, if we eat a lot of meat, including poultry and fish, milk, cheese, and eggs, we can foster the growth of bacteria that convert the choline and carnitine in those foods into trimethylamine (TMA), which can be oxidized into TMAO and wreak havoc on our arteries, increasing our risk of heart attack, stroke, and death.

We’ve known about this “troublesome” transformation from choline into trimethylamine for more than 40 years, but that was way before we learned about the heart disease connection. Why were researchers concerned back then? Because these methylamines might form nitrosamines, which have “marked carcinogenic activity”—cancer-causing activity. So where is choline found in our diet? Mostly from meat, eggs, dairy, and refined grains. The link between meat and cancer probably wouldn’t surprise anyone. In fact, just due to the industrial pollutants, like PCBs, children probably shouldn’t eat more than about five servings a month of meats like beef, pork, or chicken combined. But, what about cancer and eggs?

Studies going back to the 1970s hinted at a correlation between eggs and colon cancer, as you can see at 2:45 in my video. That was based just on so-called ecological data, though, showing that countries eating more eggs tended to have higher cancer rates, but that could be due to a million factors. It needed to be put to the test.

This testing started in the 80s, and, by the 1990s, 15 studies had been published, of which 10 suggested “a direct association” between egg consumption and colorectal cancer, “whereas five found no association.” By 2014, dozens more studies had been published, confirming that eggs may indeed be playing a role in the development of colon cancer, though no relationship was discovered between egg consumption and the development of precancerous polyps, which “suggested that egg consumption might be involved in the promotional” stage of cancer growth—accelerating cancer growth—rather than initiating the cancer in the first place.

This brings us to 2015. Perhaps it’s the TMAO made from the choline in meat and eggs that’s promoting cancer growth. Indeed, in the Women’s Health Initiative study, women with the highest TMAO levels in their blood had approximately three times greater risk of rectal cancer, suggesting that TMAO levels “may serve as a potential predictor of increased colorectal cancer risk.”

As you can see at 4:17 in my video, though there may be more evidence for elevated breast cancer risk with egg consumption than prostate cancer risk, the only other study to date on TMAO and cancer looked at prostate cancer and did indeed find a higher risk.

“Diet has long been considered a primary factor in health; however, with the microbiome revolution of the past decade, we have begun to understand how diet can” affect the back and forth between us and the rest of us inside, and the whole TMAO story is “a smoking gun” in gut bacteria-disease interactions.

Since choline and carnitine are the primary sources of TMAO production, the logical intervention strategy might be to reduce meat, dairy, and egg consumption. And, if we eat plant-based for long enough, we can actually change our gut microbial communities such that we may not be able to make TMAO even if we try.

“The theory of ‘you are what you eat’ finally is supported by scientific evidence.” We may not have to eat healthy for long, though. Soon, Big Pharma hopes, “we may yet ‘drug the microbiome’…as a way of promoting cardiovascular health.”

What did the egg industry do in response to this information? Distort the scientific record. See my video Egg Industry Response to Choline and TMAO.


This is not the first time the egg industry has been caught in the act. See, for example:

For background on TMAO see my original coverage in Carnitine, Choline, Cancer, and Cholesterol: The TMAO Connection and then find out How to Reduce Your TMAO Levels. Also, see: Flashback Friday: How to Reduce Your TMAO Levels.

This is all part of the microbiome revolution in medicine, the underappreciated role our gut flora play in our health. For more, see: 

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

How to Avoid BPA

The purported link between obesity and hormone-disrupting plastics chemicals like bisphenol A (BPA) was initially based in part on observations that the rise in chemical exposure seemed to coincide with the rise of the obesity epidemic, but that may only be a coincidence. Many other changes over the last half century, like an increase in fast-food consumption and watching TV, would seem to be simpler explanations. But why are our pets getting fatter, too? Fido isn’t drinking more fries or drinking more soda. Of course, the more we watch Seinfeld reruns, the less we may walk the dog, but what about our cats? They’re also getting fatter. Are we giving both them and our kids a few too many treats? That would seem to be an easier explanation than some pervasive obesity-causing chemical in the environment building up in the pet and person food chains.

How then do we explain the results of a study of more than 20,000 animals from 24 populations, showing they are all getting fatter? The odds that this could happen just by chance is about 1 in 10 million. The study’s “findings reveal that large and sustained population increases in body weight” are occurring across the board, even in those without access to vending machines or getting less physical education in schools. Perhaps some environmental pollutant is involved. I discuss this in my video How to Avoid the Obesity-Related Plastic Chemical BPA.

We’re exposed to a whole cocktail of new chemicals besides BPA, but the reason researchers have zeroed in on it is because of experiments showing that BPA can accelerate the production of new fat cells, at least in a petri dish. This was at more than a thousand times the concentration found in most people’s bloodstream, though. We didn’t know if the same thing happened at typical levels…until now. Most people have between 1 and 20 nanomoles of BPA in their blood, but even 1 nanomole may significantly boost human fat cell production. So, even low levels may be a problem, but that’s in a petri dish. What about in people?

Why not just measure the body weights of a population exposed to the chemical compared to a population not exposed to the chemical? There is virtually no unexposed population: BPA is everywhere. In that case, how about those with higher levels compared to those with lower levels? This is what researchers at New York University did, and the amount of BPA flowing through the bodies of children and adolescents “was significantly associated with obesity.” However, since it was a cross-sectional study, a snapshot in time, we don’t know which came first. Maybe instead of the high BPA levels leading to obesity, the obesity led to high BPA levels, since the chemical is stored in fat. Or, perhaps BPA is a marker for the same kinds of processed foods that can make you fat. What we need are prospective studies that measure exposure and then follow people over time. We never had anything like that…until now! And indeed, researchers found that higher levels of BPA and some other plastics chemicals were significantly associated with faster weight gain over the subsequent decade. So, how can we stay away from the stuff?

Though we inhale some from dust and get some through our skin touching BPA-laden receipts, 90 percent of exposure is from our diet. How can we tell? When we have people fast and drink water only out of glass bottles for a few days, their BPA levels drop as much as tenfold.

Fasting isn’t very sustainable, though.

What happens with a three-day fresh foods intervention, where families switch away from canned and packaged foods for a few days? A significant drop in BPA exposure. If we do the experiment the other way, adding a serving of canned soup to people’s daily diet, we see a thousand percent rise in BPA levels in their urine compared to a serving of soup prepared with fresh ingredients. That study used a ready-to-serve canned soup, which, in the largest survey of North American canned foods, was found to have about 85 percent less BPA than condensed soups, but the worst was canned tuna.


I previously touched upon bisphenol A in BPA Plastic and Male Sexual Dysfunction. Some companies make canned foods without BPA, for example, Eden Foods. (See Do Eden Beans Have Too Much Iodine? for more information.) You can also buy aseptic packaged beans or boil your own. Personally, I like pressure-cooking them.

For more on BPA, see:

Phthalates are another concerning class of plastics chemicals. I covered those in Avoiding Adult Exposure to Phthalates and What Diet Best Lowers Phthalate Exposure?.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Where to Buy Tea Low in Lead

China burns about half of the world’s coal, spewing heavy metals such as mercury and lead into the atmosphere that affect the development of neighboring children. What if you don’t live in China or eat anything produced there? You could still be exposed to the mercury that settles in the oceans if you eat fish and other seafood. What if you drink something from China? Tea. China is one of the world’s biggest tea exporters, but their rapid industrialization has raised concerns about contamination with lead, a toxin that can affect almost every organ in the body. The more lead there is in the soil, the more lead there is that ends up in the tea leaves. And, the closer to the highway the tea is grown, the higher the lead levels. This suggests that leaded gas, which wasn’t banned in China until the year 2000, may be playing a role in the contamination of tea grown there.

Just like larger and longer-living fish accumulate more mercury, longer-living tea leaves accumulate more lead. Young tea leaves appear to have two to six times less lead than mature leaves, so the young leaves that are used to make green and white tea have significantly less lead than the older leaves used to make black and oolong tea. As well, the lead in black and oolong tea appears to be released much more readily into the tea water when brewed. This means the health risk from lead may be 100 times lower for green tea compared to oolong and black.

Because certain fungicides may have heavy metal impurities, one might assume organic teas would be less contaminated. However, a study of 30 common teas taken from North American store shelves showed no less toxic element contamination in organic teas than regular teas, though, organic teas would presumably have much less pesticide contamination. In terms of lead, the source of the tea—that is, the country of origin—appears to be the most important factor.

So, how much tea is safe to drink? Based on the most stringent safety limits in the world, such as California’s Prop 65 parameters, and the largest studies of tea lead contamination from around the world, I was able to come up with guidelines I outline in my video Lead Contamination of Tea.

If you’re not pregnant and drinking only green tea, it doesn’t matter where you get your tea. You can drink as much as you want, as long as you’re drinking the green tea and throwing away the leaves or bags. Given the average levels of lead in Chinese black tea samples, however, more than three cups a day would exceed the daily safety limit for lead. What if you’re eating tea leaves—for example, drinking matcha tea, which is powdered green tea—or throwing tea leaves into your smoothie like I do? In that case, two or three heaping teaspoons is the limit. The exception is Japanese green tea, which is so low in lead that you can safely eat 15 spoonfuls per day, but I caution consuming more than 8 teaspoons given the risk of exceeding the daily recommended limit for caffeine intake for adults.

What about children? For a 70-pound 10-year-old, lead isn’t a problem if they’re drinking green tea. But the safe caffeine intake for children is probably around three milligrams per kilogram, which would limit a child to about four cups of green tea per day. For caffeine reasons, I recommend adding no more than two spoonfuls of Japanese green tea to a child’s smoothie. And for lead reasons, children should have no more than one teaspoon of Chinese green tea leaves. When it comes to black tea, children shouldn’t drink more than one cup per day and should not eat the tea leaves at all.

Pregnant women should be able to drink one cup of green tea per day throughout pregnancy, regardless of source. The limit for Japanese green tea is really just the caffeine limit of about four cups per day. I do not recommend drinking black tea during pregnancy or eating any kind of tea leaves, unless you know you’re getting tea from a low lead source.


I’ve long been an advocate of teas, but the information I’ve shared with you here has led me to change my daily diet. If you look at my smoothie recipe in A Better Breakfast, for example, you’ll see I’ve recommended throwing in tea leaves, and Is Matcha Good for You? doesn’t hide the fact that I’ve been a big fan of matcha. I still enjoy both, but am now more careful about where my tea is sourced. As soon as I learned of this, I made announcements on Facebook, Twitter, and Google+ to inform everyone. So, if you closely follow my recommendations (which I elaborate on extensively in my book, How Not to Die), please make sure to keep an eye on our social media where I can post updates within minutes of learning about the latest news.

I’ve got a whole slew of tea videos, including:

Where else might you find heavy metal risk (besides my music collection :)?

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

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