What Meat and Eggs Do to Our Microbiome

As I’ve explored before, whether young or old, male or female, smoker or non-smoker, with high blood pressure or low blood pressure, high cholesterol or low, having high levels of a toxic compound called TMAO—trimethylamine oxide—in the bloodstream is associated with a significantly higher risk of having a heart attack, stroke, or dying over a three-year period. Where does TMAO come from? As I investigate in my video How to Develop a Healthy Gut Ecosystem, the choline in foods like eggs can be turned by gut bacteria into TMAO, which is then absorbed back into our system. And, the more eggs we eat, the higher the levels climb, as you can see at 0:41 in my video.

Given the similarity in structure between carnitine and choline, Cleveland Clinic researchers wondered if carnitine found in red meat, energy drinks, and supplements might also lead to TMAO production and put it to the test. As you can see at 1:00 in my video, if you feed omnivores, those who regularly eat meat, a steak, their TMAO levels shoot up. Those who eat strictly plant-based may start out with almost no TMAO in their system, presumably because they’re not eating any meat, eggs, or dairy. But, even if vegans eat a sirloin, still almost no TMAO is made. Why? Presumably, they don’t have steak-eating bacteria in their guts. Indeed, it was found that no TMAO is produced if you don’t have TMAO-producing bacteria in your gut. If you don’t regularly eat meat, then you’re not fostering the growth of the meat-eating microbes that produce TMAO.

This suggests that once we develop a plant-based gut ecosystem, our bacteria will not produce TMAO, even if we eat meat every once and awhile. However, we still don’t know how rapidly gut bacteria shift after a shift in our diet—but it does not appear to be all or nothing. If men eating the standard American diet are given two sausage, egg, and cheese biscuits before and after just five days of eating lots of similarly high-fat meals, their TMAO production boosts even higher, as you can see at 2:09 in my video. So, it’s not just whether we have the bad bugs or not. Apparently, we can breed more of them the more we feed them.

Meat-free diets, on the other hand, can also have been “demonstrated to have a profound influence on human metabolism.”Just by analyzing a urine sample, we can tell what kind of diet people eat, based on measurements like how low TMAO levels are in the urine of those eating egg-free vegetarian diets, as you can see at 2:26 in my video. At 2:43 in my video, you’ll see that we can even take the same people rotate them through three different diets, and determine who is on a high-meat diet, low-meat diet, or no-meat diet, based in part on the different compounds churned out by the different gut flora or different flora activity after just about two weeks on the different diets. It’s possible that some of the beneficial effects of whole plant foods may be mediated by the effects they have on our gut bacteria. At the same time, the standard American diet may increase the relative abundance of undesirables that produce toxic compounds including TMAO (as you can see at 3:07 in my video).

Strictly plant-based diets have gained acceptance as a dietary strategy for preventing and managing disease. Perhaps, in part, this is because of their rather unique gut flora, with less of the disease-causing bacteria and more of the protective species. So, all along, we thought the reason those eating plant-based had lower heart disease rates was because they were eating less saturated fat and cholesterol, but maybe their lower TMAO levels may also be contributing to their benefits, thanks to their reduced ingestion of carnitine and choline.

I talked about the egg industry response to the choline revelation in Egg Industry Response to Choline and TMAO. How has the carnitine supplement industry reacted? In response to the research implicating carnitine in TMAO production, the former vice president of AdvoCare—a multilevel marketing company that sells carnitine supplements like AdvoCare Slam while getting slammed with lawsuits finding them guilty of being “engaged in false, misleading or deceptive acts or practices” and forced to pay more than a million dollars—questioned whether there was a secret vegan conspiracy at the Cleveland Clinic. Restricting our intake of meat or carnitine supplements to prevent our gut bacteria from making TMAO, he argued, is like trying to prevent car accidents by restricting the sale of fuel.

Okay…but there are benefits to transportation. We’re talking about TMAO, which may be fueling our epidemic of heart disease, the number-one killer of men and women in this country. As far as I’m concerned, the more we can cut the fuel for that, the better.


For more background on TMAO, see Carnitine, Choline, Cancer, and Cholesterol: The TMAO Connection, then find out How to Reduce Your TMAO Levels.

Our gut flora are what we eat. Check out:

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:

Using Green Tea to Help Prevent Cancer and Treat Cancer

Tea consumption is associated with a reduced risk of heart disease, stroke, and premature death in general, with each additional cup of green tea a day associated with a 4-percent lower mortality risk. So, perhaps “drinking several cups of tea daily can keep the doctor away,” as well as the mortician—but what about cancer?

As I discuss in my video Can Green Tea Help Prevent Cancer, there is “growing evidence from laboratory, epidemiologic [population], and human intervention studies that tea can exert beneficial disease-preventive effects” and, further, may actually “slow cancer progression.” Let’s review some of that evidence.

Not only do those who drink a lot of tea appear to live longer than those who drink less, as you can see at 0:49 in my video, drinking lots of tea may also delay the onset of cancer. At 0:56 in my video, you can see a table titled “Average age at cancer onset and daily green tea consumption.” The green tea intake is measured in Japanese tea cups, which only contain a half a cup, so the highest category in the table is actually greater than or equal to five full cups of tea, not ten as it appears in the table. Women who did get cancer appeared to get it seven years later if they had been drinking lots of tea compared to those who had consumed less. Men, however, had a three-year delay in cancer onset if they had consumed more than five full cups of green tea daily, the difference potentially “due to higher tobacco consumption by males.”

Green tea may be able to interfere with each of the stages of cancer formation: the initiation of the first cancer cell, promotion into a tumor, and then subsequent progression and spread, as you can see at 1:24 in my video. Cancer is often initiated when a free radical oxidizes our DNA, causing a mutation, but, as you can see at 1:44 in my video, we can get a nice “spike of antioxidant power” of our bloodstream within 40 minutes of drinking green tea. “This increase may, in turn, lower oxidative damage to DNA and so decrease risk of cancer.”

Furthermore, in terms of genoprotective effects—that is, protecting our genes—pre-existing oxidation-induced DNA damage was lower after drinking green tea, suggesting consumption can boost DNA repair as well. We didn’t know for certain, however…until now.

There is a DNA-repair enzyme in our body called OGG1. As you can see at 2:15 in my video, within one hour of drinking a single cup of green tea, we can boost OGG1’s activity, and after a week of tea drinking, we can boost it even higher. So, “regular intake of green tea has additional benefits in the prevention and/or repair of DNA damage.” In fact, tea is so DNA-protective it can be used for sperm storage for fresh samples until they can be properly refrigerated.

What’s more, tea is so anti-inflammatory it can be used for pain control as a mouthwash after wisdom tooth surgery, as you can see at 2:41 in my video. In terms of controlling cancer growth, at a dose of green tea compounds that would make it into our organs after drinking six cups of tea, it can cause cancer cells to commit suicide—apoptosis (programmed cell death)—while leaving normal cells alone. There are a number of chemotherapy agents that can kill cancer through brute force, but that can make normal cells vulnerable, too. So, “[g]reen tea appears to be potentially an ideal agent for [cancer] prevention”: little or no adverse side-effects, efficacious for multiple cancers at achievable dose levels, and able to be taken orally. We have a sense of how it works—how it stops cancer cells from growing and causing them to kill off themselves—and it’s cheap and has a history of safe, acceptable use. But, all of this was based on in-vitro studies in a test tube. “It needs to be evaluated in human trials,” concluded the researchers. Indeed, what happens when we give green tea to people with cancer? Does it help?

Tea consumption may reduce the risk of getting oral cancer. Not only may the consumption of tea boost the antioxidant power of our bloodstream within minutes and decrease the amount of free-radical DNA damage throughout our systems over time, but it can also increase the antioxidant power of our saliva and decrease the DNA damage within the inner cheek cells of smokers, though not as much as stopping smoking all together. You can see several graphs and tables showing these findings in the first 35 seconds of my video Can Green Tea Help Treat Cancer?.

Might this help precancerous oral lesions from turning into cancerous oral lesions? More than 100,000 people develop oral cancer annually worldwide, with a five-year overall survival rate of less than the flip of a coin. Oral cancer frequently arises from precancerous lesions in the mouth, each having a few percent chance of turning cancerous every year. Can green tea help?

Fifty-nine patients with precancerous oral lesions were randomized into either a tea group, in which capsules of powdered tea extract were given and their lesions were painted with green tea powder, or a control group, who essentially got sugar pills and their lesions painted with nothing but glycerin. As you can see at 1:23 in my video, within six months, lesions in 11 out of the 29 in the tea group shrunk, compared to only 3 of 30 in the placebo group. “The results indicate that tea treatment can improve the clinical manifestations of the oral lesions.”

The most important question, though, is whether the tea treatment prevented the lesions from turning cancerous. Because the trial only lasted a few months, the researchers couldn’t tell. When they scraped some cells off of the lesions, however, there was a significant drop in DNA-damaged cells within three months in the treatment groups, suggesting that things were going in the right direction, as you can see at 1:46 in my video. Ideally, we’d have a longer study to see if they ended up with less cancer and one that just used swallowed tea components, since most people don’t finger-paint with tea in their mouths. And, we got just that.

As you can see at 2:15 in my video, there were the same extraordinary clinical results with some precancerous lesions shrinking away. What’s more, the study lasted long enough to see if fewer people actually got cancer. The answer? There was just as much new cancer in the green tea group as the placebo group. So, the tea treatment resulted in a higher response rate, as the lesions looked better, but there was no improvement in cancer-free survival.

These studies were done on mostly smokers and former smokers. What about lung cancer? As you can see at 2:46 in my video, population studies suggest tea may be protective, but let’s put it to the test. Seventeen patients with advanced lung cancer were given up to the equivalent of 30 cups of green tea a day, but “[n]o objective responses were seen.” In a study of 49 cancer patients, 21 of whom had lung cancer, the subjects received between 4 and 25 cups worth of green tea compounds a day. Once again, no benefits were found. The only benefit green tea may be able to offer lung cancer patients is to help lessen the burns from the radiation treatments when applied on the skin. Indeed, green tea compresses may be able to shorten the duration of the burns, as you can see at 3:21 in my video.

The protective effects of green tea applied topically were also seen in precancerous cervical lesions, where the twice-a-day direct application of a green tea ointment showed a beneficial response in nearly three-quarters of the patients, compared to only about 10 percent in the untreated control group, which is consistent with the benefits of green tea compounds on cervical cancer cells in a petri dish. When women were given green tea extract pills to take, however, they didn’t seem to help.

I talked about the potential benefit of green tea wraps for skin cancer in Treating Gorlin Syndrome with Green Tea, but is there any other cancer where green tea can come into direct contact? Yes. Colon cancer, which grows from the inner surface of the colon that comes into contact with food and drink. As you can see at 4:13 in my video, in the colon, tea compounds are fermented by our good gut bacteria into compounds like 3,4DHPA, which appears to wipe out colon cancer cells, while leaving normal colon cells relatively intact in vitro. So one hundred thirty-six patients with a history of polyps were randomized to get green tea extract pills or not. Now, this study was done in Japan, where drinking green tea is commonplace, so, effectively, this was comparing those who drank three cups of green tea a day to subjects who drank four daily cups. A year later on colonoscopy, the added-green tea group had only half the polyp recurrence and the polyps that did grow were 25 percent smaller. With such exciting findings, why hasn’t a larger follow-up study been done? Perhaps due to the difficulty “in raising funds” for the study, “because green tea is a beverage but not a pharmaceutical.”

There is good news. Thanks to a major cancer charity in Germany, researchers are currently recruiting for the largest green tea cancer trial to date, in which more than 2,000 patients will be randomized. I look forward to presenting the results to you when they come in.


What about prostate cancer? See my videos Preventing Prostate Cancer with Green Tea and Treating Prostate Cancer with Green Tea.

You may also be interested in these somewhat older videos:

How interesting was that about wisdom teeth? Green tea can also be used as an anti-cavity mouth rinse, which I discuss in my video What’s the Best Mouthwash?.

Is Caffeinated Tea Dehydrating? Watch the video to find out.

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:

The Foods to Avoid to Lower Stroke Risk

“Stroke remains one of the most devastating of all neurological diseases,” killing about 5 million people a year worldwide, and is “the leading cause of permanent disability in the USA.” But the good news is that about 80 percent of stroke risk may be due to basic lifestyle factors: primarily, improving our diet, stopping smoking, and getting regular exercise.

The best way to stop smoking, evidently, is to have a heart attack. Certainly, once dead, you can’t smoke. Of those who survive a heart attack, strong, repeated advice from their doctor may persuade up to two-thirds to quit and never smoke again in any form as long as they live. “Yes, quitting smoking is very difficult. It doesn’t matter; it has to be done. If you were walking along the lakeshore and one of your grandchildren is drowning, it doesn’t take will power to go into the lake; it just has to be done.” It’s like a healthy diet: Some things just have to be done. Getting up at night to feed a baby can be difficult, too, but it’s not a matter of having willpower—some things in life just have to be done. After all, what we regularly eat every day is indeed a matter of life and death.

For stroke prevention, that means eating a more plant-based diet, like a traditional Mediterranean diet centered around whole grains, fruits, vegetables, lentils, beans, and nuts, as I discuss in my video Best Foods to Reduce Stroke Risk. A vegetarian or vegan diet may also work, but it must be accompanied by a regular, reliable source of vitamin B12, meaning B12-fortified foods or supplements. “Unfortunately, recommending taking B12 supplements may meet opposition among vegetarians because misconceptions regarding this nutrient are prevalent. Many individuals still hold on to the old myth that deficiency of this vitamin is rare and occurs only in a small proportion of vegans…Future studies with vegetarians should focus on identifying ways of convincing vegetarians to routinely take vitamin B12 supplements in order to prevent a deficiency.” The research is clear on that.

What is it about plant-based diets that make them beneficial for stroke prevention? In my video How to Prevent a Stroke, I talked about the role of fiber, which potentially leads to about a 1 percent drop in risk for every 1 gram of fiber ingested per day. Or, even better: A 12 percent drop in risk is associated with every extra 10 grams of fiber a day. In fact, fiber from whole grains is associated with a lower chance of dying not only from heart attack and stroke, but also cancer, diabetes, and respiratory diseases, as well as a lower risk of dying from infections or other causes––in other words, a lower risk of dying prematurely from all causes combined. Why? Perhaps because of the anti-inflammatory effects of fiber, which could explain how it could help across the board. Or, it could be that eating fiber means eating fewer pro-inflammatory foods. Those who eat more whole plant foods, which are where fiber is found, may be eating less processed and animal foods. In fact, the study immediately preceding the meta-analysis of fiber was a meta-analysis on meat, which looked at red meat and processed meat, and found about a 10 percent increased risk for stroke associated with each three and a half ounce daily portion, which is about the size of a deck of playing cards, or about 10 percent increased risk for every “half-deck” of processed meat.

Perhaps this occurs because of the heme iron—the blood and muscle iron—in meat, or because of “its pro-oxidative properties.” (No association was found between stroke and non-heme iron, which is the type of iron that predominates in plants.) Or, perhaps it’s because of some of the toxic pollutants like PCBs that can build up in animal fats. We’ve known, for example, that living next to a toxic waste dump might increase stroke risk, but only recently have we realized that dietary exposure even at so-called safe levels might increase stroke risk—and increase it by as much as eight or nine times for those with the highest levels of these pollutants in their bloodstream.


For more on how to reduce stroke risk with diet, see:

What does vitamin B12 have to do with stroke? Watch my video Vitamin B12 Necessary for Arterial Health to find out.

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: