Nutritional yeast is a deactivated yeast, meaning that yeast cells are killed during processing and inactive in the final product.

It’s described as having a nutty, cheesy, and savory flavor and is a common vegan cheese substitute.

Nutritional yeast comes in the form of powder or flakes. It’s an excellent source of many vitamins and minerals and offers a number of potential health benefits.

While nutritional yeast is a valuable addition to many diets, there may be some side effects associated with using it as a dietary supplement.

Here are 4 potential side effects and dangers of nutritional yeast.

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Though nutritional yeast is low in calories, it’s packed with fiber.

In fact, just 2 tablespoons (21 grams) of nutritional yeast flakes provide about 5 grams of dietary fiber — about 20% of the recommended intake (1).

A high-fiber diet can promote bowel regularity, but it’s important to increase your fiber consumption gradually (2).

Introducing too much fiber too quickly can lead to abdominal discomfort — such as cramps or even diarrhea — especially if you’re not used to eating high-fiber foods.

Since nutritional yeast packs a lot of fiber in one serving, it’s best to start slow and adjust servings as your body adapts to the higher fiber consumption.

When increasing your fiber intake, it’s always best to make sure you’re consuming adequate fluids as well to maintain proper digestion (3).

Summary Nutritional yeast is an excellent source of dietary fiber. Due to its high fiber content, it’s best to introduce nutritional yeast gradually to avoid abdominal discomfort.

While nutritional yeast is a great source of many vitamins and minerals — such as vitamin B12 and zinc — some yeast products contain compounds like tyramine and monosodium glutamate (MSG), which may trigger migraine attacks in some individuals.

Tyramine

Tyramine is a compound derived from the amino acid tyrosine and found naturally in nutritional yeast and concentrated yeast products like Vegemite (4, 5).

Most individuals can enjoy tyramine-containing foods without experiencing negative side effects.

However, some studies show that tyramine may cause migraine attacks in certain people (6, 7, 8, 9).

Migraine is a condition characterized by recurring, often debilitating headaches that cause moderate to severe pain.

Researchers are still trying to understand how tyramine triggers migraine attacks.

Still, it appears that tyramine may act on the central nervous system. It releases various hormones, which may lead to an increase in blood pressure and cause headaches (5, 10).

Monosodium Glutamate

Monosodium glutamate (MSG) is a popular food additive used to enhance flavor. Many people report MSG as a migraine trigger.

While the reasons remain unclear, MSG consumed in very large doses may interact with certain brain neurons, which can lead to headaches or dizziness (11).

MSG is only present in nutritional yeast if it has been added during processing or manufacturing.

Nutritional yeast also contains glutamic acid, but naturally occurring glutamic acid does not appear to be as readily absorbed as the glutamic acid found in MSG (12, 13).

It’s currently unclear if natural, free-standing glutamate causes the same symptoms as MSG.

However, if you consider yourself glutamate sensitive, you may want to avoid nutritional yeast due to the natural presence of glutamic acid.

Summary Nutritional yeast may contain compounds like tyramine and MSG that can trigger headaches in some people. Individuals with migraine may want to avoid nutritional yeast for this reason.

Nutritional yeast is an excellent source of niacin.

Just 1 tablespoon (11 grams) of nutritional yeast flakes provides over 38 mg of niacin, which is more than double the daily value for both men and women (1, 14).

Niacin — also known as vitamin B3 — is involved in many vital processes in your body, such as metabolism and enzyme function (15).

Still, consuming large amounts of niacin may cause facial flushing (16).

It’s characterized as a flush of red on the skin, which may be followed by a burning and itching sensation that occurs within 10–20 minutes after ingesting niacin in high doses.

While facial flushing may be uncomfortable, it’s generally not associated with harm and typically subsides within 1–2 hours (17).

Furthermore, facial flushing generally only occurs after consuming extremely high doses of niacin — such as 500 mg or more — which can usually only be reached in supplement form (18).

Although facial flushing is not dangerous, high doses of niacin can cause other, more dangerous side effects, such as liver failure. However, this is rare (19).

Facial flushing from nutritional yeast most likely wouldn’t occur after consuming only a few servings. It’s more typical after ingesting very large doses.

Summary Nutritional yeast is an abundant source of niacin. Although facial flushing is not associated with harm, consuming large doses of niacin can cause other, potentially harmful side effects.

Though relatively uncommon, some people may be intolerant to nutritional yeast.

It appears this may be most common in individuals with inflammatory bowel disease (IBD), such as Crohn's disease.

For example, one study observed that feeding mice brewer’s yeast aggravated symptoms of IBD (20).

These symptoms included weight loss, severe diarrhea, and fatigue.

While brewer’s yeast is technically a different product than nutritional yeast, it’s made from the same species of yeast.

Additionally, a handful of studies show that people with Crohn's disease may be more sensitive to dietary yeast (21, 22).

Ultimately, larger clinical studies are needed to determine whether nutritional yeast worsens IBD symptoms in humans.

Summary Brewer’s yeast — made from the same species of yeast as nutritional yeast — has been shown to exacerbate IBD symptoms in mice. Additionally, human studies have shown that people with IBD may be more sensitive to dietary yeast.

Nutritional yeast is a deactivated form of yeast full of vitamins, minerals, and nutrients.

It has a savory, cheesy flavor and can easily be added to a number of different meals and snacks.

Although nutritional yeast is generally safe for most people, it may cause adverse reactions in sensitive individuals.

In large doses, it can cause digestive discomfort or facial flushing due to its high fiber and niacin content, respectively.

Nutritional yeast may also contain tyramine and MSG, which can trigger headaches in some individuals.

It’s best to introduce nutritional yeast slowly into your diet and stick to lower doses of supplements to minimize unwanted side effects.