Is Nutritional Yeast Healthy for Everyone?

Those with certain autoimmune diseases such as Crohn’s disease should probably not eat nutritional yeast.

Thousands of years ago, some yeast floated down into our flour and drinks, pleasing our palates, and we’ve been regularly exposed to it ever since. Yeast isn’t a problem for most people, but even non-disease-causing microbes could potentially trigger autoimmune diseases like Crohn’s disease in those who are susceptible because their finely tuned immune balance is somehow off. Maybe that’s why bakers have the highest Crohn’s disease mortality and, from a different data set, also have among the highest rates of Crohn’s disease, as you can see at 0:30 in my video Is Nutritional Yeast Healthy for Everyone? Perhaps a “hypersensitivity to baker’s yeast…may play a role in Crohn’s disease.”

If you take people with Crohn’s and remove from their diets the three foods to which they appear to have the most antibodies, in order to try to calm their disease, and then add those foods back, you can provoke the symptoms once again and re-stimulate the inflammation. So, for example, an anal fistula gets nice and dry off those foods, starts oozing again once the foods are back in the diet, and then the spigot’s turned back off when the foods are removed once more, as you can see (ew!) at 0:57 in my video.

However, without a control group, you can’t exclude the possibility of a powerful placebo effect. There hadn’t been any such randomized controlled trials until researchers came up with a brilliant design. They tested people with Crohn’s for antibodies to 16 different foods and then randomized the subjects into two groups. Both groups were told to avoid four foods, but one group was told to avoid the four foods they reacted most to, while the other group was told to avoid the foods they reacted least to. The group assignments were given in sealed envelopes, so no one knew who was in which group until the end. So, did it matter? Yes, more than twice the probability of major clinical improvement was seen in the group told to stay away from the four foods their blood reacted most to—but that wasn’t just yeast. In fact, the “exclusion of milk, pork, beef, and egg was most strongly associated with improvement,” leading the researchers to suggest that perhaps instead of doing fancy blood tests, we should just tell our patients to cut out meat and eggs and see how they do. This would be consistent with population studies that associate “diets high in animal fat” with an increased risk of inflammatory bowel diseases, as well as interventional studies showing that a plant-based diet, in which meat is cut down to about one serving every two weeks, can drop relapse rates as low as an extraordinary 8 percent over two years.

But, what about the whole yeast question? Can’t you just put some yeast up someone’s butt and see what happens? Why, yes! Yes, you can, and researchers have. Indeed, researchers tested rectal exposure to six different foods, including yeast, in Crohn’s disease patients. This was kind of like a skin prick test, but instead of pricking the skin, they pricked the inside of people’s rectums with various foods. You can see at 3:00 in my video the various prick sites for the different foods, and it’s clear that yeast gave the most significant reaction in Crohn’s patients.

It appears that baker’s yeast, which is the same yeast as brewer’s yeast and nutritional yeast, may indeed have disease-causing importance in Crohn’s disease, but the good news would then be that it “may be of therapeutic relevance.” If Crohn’s patients went on a yeast-free diet, would they feel better? You don’t know until you put it to the test.

In fact, that’s exactly what the original study linking yeast and Crohn’s disease suggested back in 1988. “A controlled trial of a yeast free diet for patients with Crohn’s disease may therefore be worth while.” Why did it take years before such a study was done? Well, who’s going to fund it? Big Soda Bread? Thankfully, there are charities like the National Association for Colitis and Crohn’s disease, willing to put up the (yeast-free) dough.

Nineteen patients with Crohn’s disease ate their regular diet for a month and were then switched to a yeast-exclusion diet. There was a significantly higher CDAI, Crohn’s Disease Activity Index, which assesses symptoms like abdominal pain and diarrhea, during the period when they were eating yeast, compared to the yeast-free period. So, there was worse disease activity with yeast than without. Okay, but what was this yeast-free diet? They didn’t just cut out bread and beer. The researchers switched people from dairy milk to soy milk and from white flour to whole wheat, for example. Just cutting out milk can sometimes help with inflammatory bowel disease, as you can see at 4:43 in my video.

So, with so many dietary changes, how do we know what role the yeast played? This is how we know what role the yeast played: After placing the subjects on the new yeast-free diet, they then challenged the Crohn’s sufferers with either a capsule of yeast or a placebo. A tiny amount of yeast, like giving them a quarter teaspoon of nutritional yeast a day, made them worse, suggesting “yeast may be important in the pathogenesis [disease process] of Crohn’s disease.”

Now, for the vast majority of people, yeast is not a problem, but in susceptible individuals, it may trigger an abnormal immune response in the gut. But, wait. I thought the paratuberculosis bug was considered a trigger for Crohn’s disease. Well, maybe infection with paraTB is what “induces a hypersensitivity response to dietary yeast.” Who knows? The bottom line is that people with Crohn’s disease should not go out of their way to add baker’s, brewer’s, or nutritional yeast to their diets.

I introduced this topic in Does Nutritional Yeast Trigger Crohn’s Disease?, then took a bit of a tangent with Is Candida Syndrome Real?. Next, I finish up this video series by talking about another autoimmune disease that appears to be affected: Dietary Cure for Hidradenitis Suppurativa.


For more on Crohn’s, see Preventing Crohn’s Disease with Diet and Dietary Treatment of Crohn’s Disease

And paratubercuwhat? See Does Paratuberculosis in Milk Trigger Type 1 Diabetes? and Does Paratuberculosis in Meat Trigger Type 1 Diabetes?

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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:

What About Coconuts, Coconut Milk, and Coconut Oil MCTs?

Do the medium-chain triglycerides in coconut oil and the fiber in flaked coconut counteract the negative effects on cholesterol and artery function?

Studies of populations who eat a lot of coconuts are “frequently cited” by those who sell coconut oil “as evidence that coconut oil does not have negative effects on cardiovascular health.” For example, there was an apparent absence of stroke and heart disease on the island of Kativa in Papua New Guinea. What were they eating? Their diets centered around tubers, like sweet potatoes, with fruits, greens, nuts, corn, and beans. Although they ate fish a few times a week, they were eating a largely whole food plant-based diet. It’s no wonder they may have had such low rates of artery disease. And, one of the whole foods they were eating was coconut, not coconut oil.

Now, if you go to Pukapuka, even more coconuts are eaten. In fact, as you can see at 0:51 in my video What About Coconuts, Coconut Milk, and Coconut Oil MCTs?, there’s even an island where coconuts make up most of what people eat—and they do get high cholesterol. How can a population eating 87 percent plant-based, with no dairy and only rare consumption of red meat, chicken, and eggs, have cholesterol levels over 200? Well, they’re eating all those coconuts every day. What are their disease rates like? We don’t know. There are no clinical surveys, no epidemiological death data, and no autopsies. Some EKGs were taken, which can sometimes pick up evidence of past heart attacks, but they found few abnormalities. The sample was too small to be a definitive study, though. And, even if they did have low disease rates, they weren’t eating coconut oil—they were eating coconut in its whole form.

Coconut oil proponents pointing to these studies is like the high fructose corn syrup lobby pointing to studies of healthy populations who eat corn on the cob or the sugar industry pointing to studies on fruit consumption and saying you can eat all the refined sugar you want. But fruit has fiber and so do coconuts. Just as adding psyllium fiber (Metamucil) to coconut oil can help blunt the adverse effects on cholesterol, fiber derived from defatted coconut itself can reduce cholesterol levels as much as oat bran. What’s more, the plant protein in coconuts, which is also missing from the oil, may help explain why whole coconuts may not have the same effects on cholesterol. Although coconut fat in the form of powdered coconut milk may not have the same effects on cholesterol as coconut oil, frequent consumption, defined as three or more times a week, has been associated with increased risk of vascular disease, stroke, and heart disease. And, no wonder, as coconut milk may acutely impair artery function as badly as a sausage and egg McMuffin.

Researchers tested three different meals including a Western high-fat meal that “consisted of an Egg McMuffin®, Sausage McMuffin®, 2 hash brown patties and a non-caffeinated beverage (McDonald’s Corporation)” a local high-fat meal, and an “isocaloric low-fat meal.” The study was conducted in Singapore, so the more traditional local high-fat meal was rice cooked in coconut milk and served with anchovies and an egg. These two different high-fat meals were put up against the same amount of calories in an unhealthy low-fat meal of Frosted Flakes, skim milk, and juice. At 3:21 in my video, you can see the artery function—that is, its ability to relax normally—before and after eating each of the three meals. Researchers found that artery function is significantly crippled within hours of consuming the McMuffins and also the local high-fat meal with coconut milk. So, whether the fat is mostly from meat and oil or from coconut milk, the arteries clamped down similarly, whereas that horrible sugary breakfast had no bad effect on artery function. Why? Because as terrible as the Frosted Flakes meal was, it had no saturated fat at all. (It also didn’t have contain any eggs, so that might have helped, too.)

Coconut oil proponents also try to argue that coconut oil has MCTs, medium-chain triglycerides, which are shorter-chain saturated fats that aren’t as bad as the longer-chain saturated fats in meat and dairy. You can’t apply the MCT research to coconut oil, though. Why not? Well, MCT oil is composed of MCTs—about 50 percent of the medium-chain fat caprylic acid and the other 50 percent of the MCT capric acid—whereas those MCTs make up only about 10 percent of coconut oil. Most of coconut oil is the cholesterol-raising, longer-chain saturated fats, lauric and myristic. “It is therefore inaccurate to consider coconut oil to contain either predominantly medium-chain fatty acids or predominantly medium-chain triglycerides. Thus, the evidence on medium-chain triglycerides cannot be extrapolated to coconut oil.”

It’s actually quite “a common misconception” that the saturated fat in coconut oil is comprised of mainly MCTs. Actually, as we discussed, coconut oil is mainly lauric and myristic, both of which have potent bad LDL cholesterol-raising effects. “Coconut oil should therefore not be advised for people who should or want to reduce their risk of CHD,” coronary heart disease, which is the number-one killer of U.S. men and women. The beef industry, for example, loves to argue that beef fat contains stearic acid, a type of saturated fat that doesn’t raise cholesterol. Yes, but it also has palmitic and myristic acids that, like lauric acid, do raise cholesterol, as you can see at 5:12 in my video.

If you compare the effects of different saturated fats, as you can see at 5:29 in my video, stearic acid does have a neutral effect on LDL, but palmitic, myristic, and lauric acids shoot it up—and, frankly, so may MCT oil itself, as it bumps up LDL 15 percent compared to control. Bottom line? “Popular belief”—spread by the coconut oil industry—“holds that coconut oil is healthy, a notion not supported by scientific data.” The science just doesn’t support it.

So, basically, “coconut oil should be viewed no differently” from animal sources of dietary saturated fat. A recent review published in the Journal of the American College of Cardiology put it even more simply in its recommendations for patients. When it comes to coconut oil, “avoid.”

Okay, but doesn’t saturated fat boost HDL, the so-called good cholesterol? Check out Coconut Oil and the Boost in HDL “Good” Cholesterol.


Isn’t coconut oil supposed to be good for Alzheimer’s, though? See my video Does Coconut Oil Cure Alzheimer’s?

If you want to learn more about the original McMuffin artery studies, see The Leaky Gut Theory of Why Animal Products Cause Inflammation.

You may also be interested in Flashback Friday: Coconut Oil and Abdominal Fat.

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:

What About the Trans Fat in Animal Fat?

The years of healthy life lost due to our consumption of trans fats are comparable to the impact of conditions like meningitis, cervical cancer, and multiple sclerosis. But, if “food zealots” get their wish in banning added trans fats, what’s next? I explore this in my video Banning Trans Fat in Processed Foods but Not Animal Fat.

Vested corporate interests rally around these kinds of slippery slope arguments to distract from the fact that people are dying. New York Mayor Bloomberg was decried as a “meddling nanny” for his trans fat ban and attempt to cap soft drink sizes. How dare he try to manipulate consumer choice! But isn’t that what the food industry has done? “Soft drink portion sizes have grown dramatically, along with Americans’ waistlines.” In 1950, a 12-ounce soda was the king-sized option. Now, it’s the kiddie size. Similarly, with trans fats, it was the industry that limited our choice by putting trans fats into everything without even telling us. Who’s the nanny now?

New York City finally won its trans fat fight, preserving its status as a public health leader. “For example, it took decades to achieve a national prohibition of lead paint, despite unequivocal evidence of harm,” but New York City’s Board of Health led the way, banning it “18 years before federal action.”

There’s irony in the slippery slope argument: First, they’ll come for your fries; next, they’ll come for your burger. After the trans fat oil ban, one of the only remaining sources of trans fat is in the meat itself. “Trans fats naturally exist in small amounts in the fat in meat and milk,” as I’ve discussed before in my video Trans Fat in Meat and Dairy. Before the trans fat ban, animal products only provided about one fifth of America’s trans fat intake, but since the U.S. trans fat ban exempts animal products, they will soon take over as the leading source. As you can see at 2:09 in Banning Trans Fat in Processed Foods but Not Animal Fat, now that added trans fats are banned in Denmark, for example, the only real trans fat exposure left is from animal products found in the U.S. dairy, beef, chicken fat, turkey meat, lunch meat, and hot dogs, with trace amounts in vegetable oils due to the refining process.

The question is: Are animal trans fats as bad as processed food trans fats? As you can see at 2:38 in my video, a compilation of randomized interventional trials found that they both make bad cholesterol go up and they both make good cholesterol go down. So, both animal trans fats and processed food trans fats make the ratio of bad to good cholesterol go up—which is bad. Therefore, all trans fats cause negative effects “irrespective of their origin.” The researchers suspect that also removing natural trans fats from the diet could prevent tens of thousands of heart attacks, but unlike processed foods, you can’t remove trans fats from milk and meat because trans fats are there naturally.

The livestock industry suggests that a little bit of their trans fats might not be too bad, but you saw the same everything-in-moderation argument coming from the Institute of Shortening and Edible Oils after industrial trans fats were first exposed as a threat. The bottom line is “that intake of all sources of trans fat should be minimized.” The trans fat in processed foods can be banned, and just adhering to the current dietary guidelines to restrict saturated fat intake, which is primarily found in meat and dairy, would automatically cut trans fat intake from animal fats.

The reason no progress may have been made on animal trans fat reduction in Denmark is because The Danish Nutrition Council that pushed for the trans fat ban was a joint initiative of The Danish Medical Association and The Danish Dairy Board. They recognized that “the economic support from The Danish Dairy Council could be perceived as problematic” from a scientific integrity point of view, but, not to worry—“The Danish Medical Association expanded the Executive Board and the funding members to also include the Danish pork industry, the Danish meat industry, The Poultry and Egg Council and The Danish Margarine Industry Association.”

If people want to eat trans fat, isn’t that their right? Yes, but only if they’re informed about the risks—yet The Food Industry Wants the Public Confused About Nutrition.

For more on the industry pushback, see my video Controversy Over the Trans Fat Ban.

There does not appear to be a safe level of exposure to trans fat—or to saturated fat or dietary cholesterol, for that matter. See Trans Fat, Saturated Fat, and Cholesterol: Tolerable Upper Intake of Zero.


If you find these videos about industry influence on public policy compelling, check out my many others, including:

Note that the concept of raising or lowering HDL (the so-called good cholesterol) playing a causal role in heart disease has come into question. See Coconut Oil and the Boost in HDL “Good” Cholesterol.

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: