Kidney Toxins Created by Meat Consumption

As I discuss in my video How to Treat Heart Failure and Kidney Failure with Diet, one way a diet rich in animal-sourced foods like meat, eggs, and cheese may contribute to heart disease, stroke, and death is through the production of an atherosclerosis-inducing substance called TMAO. With the help of certain gut bacteria, the choline and carnitine found concentrated in animal products can get converted into TMAO. But, wait a second. I thought atherosclerosis, or hardening of the arteries, was about the buildup of cholesterol. Is that not the case?

“Cholesterol is still king,” but TMAO appears to accelerate the process. It seems that TMAO appears to increase the ability of inflammatory cells within the atherosclerotic plaque in the artery walls to bind to bad LDL cholesterol, “which makes the cells more prone to gobble up cholesterol.” So TMAO is just “another piece to the puzzle of how cholesterol causes heart disease.”

What’s more, TMAO doesn’t just appear to worsen atherosclerosis, contributing to strokes and heart attacks. It also contributes to heart and kidney failure. If you look at diabetics after a heart attack, a really high-risk group, nearly all who started out with the most TMAO in their bloodstream went on to develop heart failure within 2,000 days, or about five years. In comparison, only about 20 percent of those starting out with medium TMAO levels in the blood went into heart failure and none at all in the low TMAO group, as you can see at 1:21 in my video.

So, those with heart failure have higher levels of TMAO than controls, and those with worse heart failure have higher levels than those with lesser stage heart disease. If you follow people with heart failure over time, within six years, half of those who started out with the highest TMAO levels were dead. This finding has since been replicated in two other independent populations of heart failure patients.

The question is, why? It’s probably unlikely to just be additional atherosclerosis, since that takes years. For most who die of heart failure, their heart muscle just conks out or there’s a fatal heart rhythm. Maybe TMAO has toxic effects beyond just the accelerated buildup of cholesterol.

What about kidney failure? People with chronic kidney disease are at a particularly “increased risk for the development of cardiovascular disease,” thought to be because of a diverse array of uremic toxins. These are toxins that would normally be filtered out by the kidneys into the urine but may build up in the bloodstream as kidney function declines. When we think of uremic toxins, we usually think of the toxic byproducts of protein putrefying in our gut, which is why specially formulated plant-based diets have been used for decades to treat chronic kidney failure. Indeed, those who eat vegetarian diets form less than half of these uremic toxins.

Those aren’t the only uremic toxins, though. TMAO, which, as we’ve discussed, comes from the breakdown of choline and carnitine found mostly in meat and eggs, may be increasing heart disease risk in kidney patients as well. How? “The cardiovascular implication of TMAO seems to be due to the downregulation of reverse cholesterol transport,” meaning it subverts our own body’s attempts at pulling cholesterol out of our arteries.

And, indeed, the worse our kidney function gets, the higher our TMAO levels rise, and those elevated levels correlate with the amount of plaque clogging up their arteries in their heart. But once the kidney is working again with a transplant, your TMAO levels can drop right back down. So, TMAO was thought to be a kind of biomarker for declining kidney function—until a paper was published from the Framingham Heart Study, which found that “elevated choline and TMAO levels among individuals with normal renal [kidney] function predicted increased risk for incident development of CKD,” chronic kidney disease. This suggests that TMAO is both a biomarker and itself a kidney toxin.

Indeed, when you follow kidney patients over time and assess their freedom from death, those with higher TMAO, even controlling for kidney function, lived significantly shorter lives, as you can see at 4:44 in my video. This indicates this is a diet-induced mechanism for progressive kidney scarring and dysfunction, “strongly implying the need to focus preventive efforts on dietary modulation,” but what might that look like? Well, maybe we should reduce “dietary sources of TMAO generation, such as some species of deep-sea fish, eggs, and meat.”

It also depends on what kind of gut bacteria you have. You can feed a vegan a steak, and they still don’t really make any TMAO because they haven’t been fostering the carnitine-eating bacteria. Researchers are hoping, though, that one day, they’ll find a way to replicate “the effects of the vegetarian diet…by selective prebiotic, probiotic, or pharmacologic therapies.”


For more on this revolutionary TMAO story, see:

For more on kidney failure, see Preventing Kidney Failure Through Diet and Treating Kidney Failure Through Diet.

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:

Topical Green Tea for Acne and Fungal Infections

Which plant should we use for which skin disease? That’s the topic of my video Natural Treatment for Acne and Fungal Infections. Thousands of studies have been published to date about the health effects of green tea, but it wasn’t until fairly recently that researchers began to look at the possibility of using green tea for the prevention and treatment of infections. Patents have been taken out on the antibacterial, antifungal, and antiviral properties of tea. Let’s review some of the evidence.

In terms of fungal infections, green tea compounds have demonstrated “potent antifungal activity” against the primary cause of athlete’s foot, fungal nail infections, jock itch, and ringworm—comparable, in some cases, to powerful antifungal drugs like fluconazole. This was shown in a petri dish, though. How about a green tea footbath for athlete’s foot fungus between the toes? Evidently, tea leaves were once used as a folk remedy for the fungus, so why not put it to the test? Indeed, a once-a-day, 15-minute dilute green tea footbath led to a significant improvement in symptoms compared to controls.

Green tea baths also appeared to help with fungus-associated atopic dermatitis, though there was no control group in that study, and a full-strength green tea may help clear candida yeast from poorly cleaned dentures. What about the bacteria that cause plaque and gingivitis? Even a 2% green tea mouthwash was found to be effective. Yes, you should be able to control plaque just with proper brushing and flossing—with an emphasis on “proper.” Most people don’t brush for the recommended four minutes a day, so a dilute green tea mouthwash may help.

In terms of plaque bacteria-killing ability, green tea was beaten out by a “garlic with lime mouth rinse,” but I think I’ll just stick to green tea, especially when green tea appears to not only kill plaque bugs directly but also boost the antibacterial capacity of saliva after you drink it.

What about green tea for acne? Six weeks of a 2% green tea lotion cut the number of pimples by more than half and significantly reduced the severity, as you can see at 2:48 in my video, making it a cheap, effective treatment for acne.

Impetigo is another bacterial skin infection that can affect the face, but a tea ointment can affect an 80 percent cure rate, on par with antibiotics given topically or orally.

What about bladder infections? We know a certain concentration of green tea compounds can kill the type of E. coli that causes urinary tract infections. The question then becomes how much tea do you have to drink to achieve those concentrations in your bladder? Not much, it turns out. Just one cup of tea might have an effect, but you may need to space out multiple cups over the day because it gets cleared out of your system within about eight hours, as you can see at 3:45 in my video.

So, where do we stand now? The test tube data look promising, but there has yet to be a single study to put it to the test. At this point, green tea should just be used as an adjunct therapy for bladder infections. But, with emerging multidrug-resistant organisms, green tea certainly holds potential.

Wait a moment. If green tea is so good at killing bacteria, might we be killing the good bacteria in our gut when we drink it? No. That’s what’s so amazing. “It has also been shown that green tea has no effect over intestinal flora, which is a great advantage against other bactericidal [bacteria-killing] agents.” But that may not actually be true. Drinking green tea may actually boost the levels of our good bacteria by acting as a prebiotic, thereby improving the colon environment, so it may actually have some effect on our gut flora after all, but it appears to be all good.


Drinking tea with meals may impair iron absorption, so it’s better to drink it between meals. For more on green tea, one of my favorite beverages, along with water and hibiscus tea, see:

For more on acne, 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:

Updating Our Microbiome Software and Hardware

Good bacteria, those living in symbiosis with us, are nourished by fruits, vegetables, grains, and beans, whereas bad bacteria, those in dysbiosis with us and possibly contributing to disease, are fed by meat, junk food and fast food, seafood, dairy, and eggs, as you can see at 0:12 in my video Microbiome: We Are What They Eat. Typical Western diets can “decimate” our good gut flora.

We live with trillions of symbionts, good bacteria that live in symbiosis with us. We help them, and they help us. A month on a plant-based diet results in an increase in the population of the good guys and a decrease in the bad, the so-called pathobionts, the disease-causing bugs. “Given the disappearance of pathobionts from the intestine, one would expect to observe a reduction in intestinal inflammation in subjects.” So, researchers measured stool concentrations of lipocalin-2, “which is a sensitive biomarker of intestinal inflammation.” As you can see at 1:13 in my video, within a month of eating healthfully, it had “declined significantly…suggesting that promotion of microbial homeostasis”—or balance—“by an SVD [strict vegetarian diet] resulted in reduced intestinal inflammation.” What’s more, this rebalancing may have played a role “in improved metabolic and immunological parameters,” that is, in immune system parameters.

In contrast, on an “animal-based diet,” you get growth of disease-associated species like Bilophila wadsworthia, associated with inflammatory bowel disease, and Alistipes putredinis, found in abscesses and appendicitis, and a decrease in fiber-eating bacteria. When we eat fiber, the fiber-munching bacteria multiply, and we get more anti-inflammatory, anti-cancer short-chain fatty acids. When we eat less fiber, our fiber-eating bacteria starve away.

They are what we eat.

Eat a lot of phytates, and our gut flora get really good at breaking down phytates. We assumed this was just because we were naturally selecting for those populations of bacteria able to do that, but it turns out our diet can teach old bugs new tricks. There’s one type of fiber in nori seaweed that our gut bacteria can’t normally breakdown, but the bacteria in the ocean that eat seaweed have the enzyme to do so. When it was discovered that that enzyme was present in the guts of Japanese people, it presented a mystery. Sure, sushi is eaten raw, so some seaweed bacteria may have made it to their colons, but how could some marine bacteria thrive in the human gut? It didn’t need to. It transferred the nori-eating enzyme to our own gut bacteria.

“Consequently, the consumption of food with associated environmental bacteria is the most likely mechanism that promoted this CAZyme [enzyme] update into the human gut microbe”—almost like a software update. We have the same hardware, the same gut bacteria, but the bacteria just updated their software to enable them to chew on something new.

Hardware can change, too. A study titled “The way to a man’s heart is through his gut microbiota” was so named because the researchers were talking about TMAO, trimethylamine N-oxide. As you can see at 3:33 in my video, certain gut flora can take carnitine from the red meat we eat or the choline concentrated in dairy, seafood, and eggs, and convert it into a toxic compound, which may lead to an increase in our risk of heart attack, stroke, and death.

This explains why those eating more plant-based diets have lower blood concentrations of TMAO. However, they also produce less of the toxin even if you feed them a steak. You don’t see the same “conversion of dietary L-carnitine to TMAO…suggesting an adoptive response of the gut microbiota in omnivores.” They are what we feed them.

As you can see at 4:17 in my video, if you give people cyclamate, a synthetic artificial sweetener, most of their bacteria don’t know what to do with it. But, if you feed it to people for ten days and select for the few bacteria that were hip to the new synthetic chemical, eventually three quarters of the cyclamate consumed is metabolized by the bacteria into another new compound called cyclohexylamine. Stop eating it, however, and those bacteria die back. Unfortunately, cyclohexylamine may be toxic and so was banned by the FDA in 1969. In a vintage Kool-Aid ad from 1969, Pre-Sweetened Kool-Aid was taken “off your grocer’s shelves,” but Regular Kool-Aid “has no cyclamates” and “is completely safe for your entire family.”

But, if you just ate cyclamate once in a while, it wouldn’t turn into cyclohexylamine because you wouldn’t have fed and fostered the gut flora specialized to do so. The same thing happens with TMAO. Those who just eat red meat, eggs, or seafood once in a while would presumably make very little of the toxin because they hadn’t been cultivating the bacteria that produce it.


Here’s the link to my video on TMAO: Carnitine, Choline, Cancer, and Cholesterol: The TMAO Connection. For an update on TMAO, see How Our Gut Bacteria Can Use Eggs to Accelerate Cancer, Egg Industry Response to Choline and TMAO, and How to Reduce Your TMAO Levels.

Interested in more on keeping our gut bugs happy? 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: