Is MSG (flavour enhancer) really bad for you?
― It's the same glutamate found in tomatoes and kelp
Many people have heard that "MSG is bad for you." Yet the substance inside it, glutamate, is found in kelp, in tomatoes, and even in the breast milk babies drink. And your body cannot tell where it came from. Let's trace where this story began, and what turned up when people actually investigated it.
You check the back of a food package at the supermarket and see "seasoning (amino acids, etc.)" listed. It sounds vaguely unhealthy, so you put it back on the shelf. Sound familiar?
Meanwhile, dashi stock made from kelp and dried bonito flakes gets held up as the picture of wholesome, natural flavour.
Actually, the substance behind the savoury taste in both is essentially the same. So where did the "bad for you" reputation come from?
Dig in, and it comes down to two things
The glutamate in MSG and the glutamate in kelp or tomatoes are exactly the same molecule, shape and all. Inside your gut, both are used in exactly the same way.
The reputation traces back to a single letter sent to a medical journal in 1968. When people were tested without knowing which one they'd eaten, no clear difference showed up.
Let's take this step by step. Along the way, we'll also find a surprising number about MSG's "salt content."
Glutamate was already there in the food
The person who worked out what causes umami was the Japanese chemist Kikunae Ikeda. In 1908, he investigated what gave kelp dashi its distinctive taste in hot tofu dishes. He found that the crystals he extracted from kelp were glutamate.
Glutamate is one of the amino acids, the building blocks of the proteins that make up your body. It's present in large amounts as part of the protein in meat, fish and beans alike. When it's freed up by ageing, fermentation, or heat, it becomes the "umami" taste you sense on your tongue.
Look at Figure 1. It shows roughly how much free glutamate is found per 100g of various foods. Kelp and grated parmesan at the top are essentially concentrated blocks of umami. Tomatoes gain more as they ripen. Notice that breast milk, at the very bottom, contains some too.
MSG is a powder made by combining sodium with glutamate produced by feeding sugar, such as from sugar cane, to microbes. Once dissolved in water, it becomes exactly the same glutamate found in kelp dashi.
What's more, most of the glutamate you eat is thought to be used on the spot as an energy source by the cells lining your small intestine. Only a tiny amount is believed to reach the bloodstream and travel around the body or to the brain.
It started with one letter, and vanished under a blindfold
In 1968, a letter from a doctor appeared in an American medical journal. It described numbness in the neck and heart palpitations after eating at Chinese restaurants. Among the suspected causes listed was the MSG used in the cooking.
The letter caused a huge stir and was even given a name: "Chinese restaurant syndrome." That's how the idea that "MSG is bad for you" spread around the world.
But when the claim was later tested carefully, the story changed. Trials were run where neither the participants nor the people handing out the samples knew whether they contained real MSG or a fake. This is called a double-blind test. And it turned out that even among people who said "I'm sensitive to it," whether symptoms appeared had almost nothing to do with what they'd actually been given.
If you believe "this will make me feel unwell," you can genuinely end up feeling unwell. Blind testing exists precisely to strip out this effect of belief. The UN's expert committee on food additives has also concluded that there is "no need" to set an upper daily limit for how much can safely be eaten.
That said, there are reports that taking several grams at once on an empty stomach, without food, slightly increased the number of people reporting temporary discomfort. Even that finding isn't clearly reproducible. And it's an entirely different order of magnitude from the amounts used in ordinary cooking.
Its sodium is about a third that of table salt
MSG contains sodium, which is why people tend to assume it's high in salt. But gram for gram, it actually has only about a third the sodium of table salt.
Try changing the amount using the slider in Figure 2. The top row shows how many tomatoes' worth of the same glutamate that represents. The bottom row compares the sodium in the same weight of table salt.
The reason so little sodium is needed comes down to molecular weight. Most of the weight of MSG powder is the glutamate part; sodium is only a small fraction of it. It's also known that when umami is strong, food tastes satisfying even with less salt. That's why MSG is sometimes used as a trick for cutting salt.
Using kelp's glutamate together with a different umami substance found in bonito flakes or dried shiitake makes the umami taste far stronger than simply adding the two together. This is called the "umami synergy effect." Combined kelp-and-bonito dashi is traditional wisdom that puts this effect to practical use.
Feeling unwell after a meal can have all sorts of causes: overeating, too much salt or alcohol, greasy food, and more. If food really is causing your symptoms, the quickest path forward is to consult a doctor rather than pinning the blame on a single ingredient yourself.
Summary
MSG contains the same glutamate found in kelp, tomatoes and cheese. The "bad for you" reputation spread from a single letter, but blind trials failed to clearly reproduce the symptoms. Its sodium content is about a third that of table salt by weight. Of course, any seasoning thrown in to excess will throw off both flavour and health.
Your body has no idea where umami came from.
If it worries you, the question isn't "from what," but "how much."
The mechanism behind taste is explained in why colds make food taste bland. The temperature of salted water is covered in does adding salt make water boil faster, and what happens in the body when nutrients run short is explained in what happens to the body without enough vitamin C.
- Pour 100mL of lukewarm water into two cups, and drop a piece of kelp into just one of them. Leave both for 30 minutes.
- Have a family member line the cups up so you don't know which is which, and taste them side by side. See if you can pick out the kelp one.
- Next, add a pinch of bonito flakes to the kelp water, strain it, and taste again. You should notice the umami become much stronger.
Not knowing "which is which" in step 2 is the same idea as the blind testing that came up in this article. Set your assumptions aside and judge with your tongue alone.
Want to know more? ― Terms, formulas, and how this connects to your textbooksWe've labelled which school level each part belongs to, from junior high science to university-level specialties
- JHSCovered in junior high school science
- HSCovered in high school "Chemistry" or "Biology"
- HS+Advanced high school content, or textbook sidebar material
- UnivNot covered in high school; university-level specialties (nutritional physiology, pharmacology, epidemiology)
- ResearchNot yet settled "textbook fact" even at university ― an active research question
JHSTerms: this phenomenon has a name
- Monosodium glutamate (MSG): the main component of the flavour enhancer. A salt formed when glutamate bonds with sodium; when dissolved in water it splits back into a glutamate part and sodium.
- Amino acid: a building block that makes up protein. Glutamate is one of them, and it's also abundant inside proteins themselves.
- Double-blind: a trial where neither the participant nor the person administering it knows which is the real substance. It removes the effect of belief.
- Nocebo effect: feeling genuinely unwell simply because you believe something will cause harm.
JHSHSCheck it with a formula: how many tomatoes is 0.5g of MSG worth?
The amount of glutamate in the powder is set by the ratio of molecular weights. When one particle (molecule) dissolves, it releases exactly one glutamate particle. The amount of sodium can be worked out the same way.
| In symbols | mG = m × ( MG ÷ M ) |
| In words | Amount of glutamate = weight of seasoning × ( molecular weight of glutamate ÷ formula weight of seasoning ) |
| Where it comes from | The ratio of chemical formulas (conservation of amount of substance). Dissolving doesn't change the number of particles, and one particle of seasoning releases one particle of glutamate, so the weights split according to the ratio of molecular weights. Sodium follows the same logic, at a ratio of 23 ÷ formula weight. |
| Symbol | Meaning and unit |
|---|---|
| m | Weight of MSG (g) |
| mG | Weight of glutamate within it (g) |
| MG | Molecular weight of glutamate (147) |
| M | Formula weight of the seasoning (monosodium glutamate monohydrate) (187) |
| Molecular weight of glutamate | 147 |
| Formula weight of monosodium glutamate monohydrate | 187 |
| Atomic weight of sodium | 23 |
| Formula weight of table salt (sodium chloride) | 58.5 |
| Glutamate in 100g of tomato (approx.) | said to be about 250 mg |
| Glutamate in 100g of grated cheese (approx.) | said to be about 1700 mg |
| Amount of seasoning used | 0.5 g |
| Glutamate proportion | 147 ÷ 187 ≒ 0.786 |
| Glutamate within 0.5g (g) | 0.5 × 0.786 ≒ 0.393 |
| Convert to milligrams | 0.393 × 1000 = 393 |
| Glutamate in one tomato (150g) (mg) | 250 × 1.5 = 375 |
| How many tomatoes is that | 393 ÷ 375 ≒ 1.05 |
| How much grated cheese instead (per-100g ratio) | 393 ÷ 1700 ≒ 0.231 |
| Convert to grams of cheese | 0.231 × 100 = 23.1 |
| Sodium proportion in the seasoning | 23 ÷ 187 ≒ 0.123 |
| Sodium proportion in table salt | 23 ÷ 58.5 ≒ 0.393 |
| Comparing the two | 0.123 ÷ 0.393 ≒ 0.31 |
The glutamate in 0.5g of MSG equals about one tomato, or about 23g of grated cheese (a few tablespoons). Its sodium is about 0.31 times that of the same weight of table salt ― roughly a third. The slider in Figure 2 uses this exact same formula.
HSHS+Glutamate as an amino acid
HSGlutamate is an amino acid with a second, acidic side chain (a carboxyl group). In water it exists in a charged form, and there's no distinction between one that came from MSG and one that came from food. It's released when protein is broken down by hydrolysis, and it's the source of umami in aged cheese, soy sauce and cured ham.
HS+The tongue has umami receptors (a pairing of T1R1 and T1R3) that bind glutamate. Inosinate and guanylate are thought to make it harder for bound glutamate to detach from the receptor, which is believed to produce the synergy effect.
UnivFirst-pass metabolism, and how the trials were designed
Glutamate taken in by mouth is thought to be consumed in large quantities as an energy source by the mucosal cells of the small intestine. This is called intestinal first-pass metabolism, and blood concentration is thought to barely rise as a result. On top of that, the brain is protected from blood-borne glutamate by the blood-brain barrier. On safety, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) judged in 1987 that an acceptable daily intake need "not be specified." Studies checking for symptoms use double-blind placebo-controlled trials and repeated-challenge designs on the same individuals. These remove the nocebo effect and chance fluctuations in how people happen to feel.
📖 For the derivation of the formula and further reading: Monosodium glutamate (Japanese Wikipedia) ／ Chinese restaurant syndrome (Japanese Wikipedia)
ResearchWhat's still not fully understood
- Is there a genuinely sensitive minority? Large trials haven't found a consistent response, but participant numbers are limited, so a small group of sensitive individuals hasn't been ruled out.
- What do the gut's umami receptors do? The same type of receptor found on the tongue also exists in the stomach and intestines, and researchers are investigating whether it plays a role in preparing for digestion or in feelings of fullness.
- Temporary discomfort from a large dose on an empty stomach. There are reports involving several grams taken at once without food, but the reproducibility and mechanism remain unclear.
In other words, this article too reflects "the best explanation available given what's currently known." That said, no consistent evidence of harm has been found for the amounts used in ordinary cooking.
How this connects to your textbooks (by level)
| Level | Subject / unit | Where in this article |
|---|---|---|
| JHS | Science, "Digestion and absorption," "Atoms and molecules" | How protein breaks down into amino acids; the logic of particle counts |
| HS | Chemistry, "Amount of substance and chemical formulas," "Amino acids and proteins" | Working out glutamate and sodium content from molecular-weight ratios |
| HS+ | Biology, "Receptors and the senses" | Umami receptors and the synergy effect |
| Univ | Nutritional physiology / epidemiology | First-pass metabolism, double-blind placebo-controlled trials, acceptable intake |
| Research | Taste and gut physiology research | Gut umami receptors, whether individual differences exist |
| ― | Everyday connections | Reading food labels, tricks for cutting salt, how to make dashi |
- Kwok, R. H. M. (1968) Chinese-Restaurant Syndrome. New England Journal of Medicine 278: 796.
- Geha, R. S. et al. (2000) Review of Alleged Reaction to Monosodium Glutamate and Outcome of a Multicenter Double-Blind Placebo-Controlled Study. Journal of Nutrition 130: 1058S–1062S.
- Ikeda, Kikunae (1909) "On a New Seasoning" (新調味料に就て) Journal of the Chemical Society of Tokyo (東京化学会誌) 30: 820–836.
- JECFA (1988) L-glutamic acid and its ammonium, calcium, monosodium and potassium salts. WHO Food Additives Series 22.
- Reeds, P. J. et al. (2000) Intestinal glutamate metabolism. Journal of Nutrition 130: 978S–982S.
- Umami Information Center (うま味インフォメーションセンター), "Umami substances found in food" (食品に含まれるうま味成分) — source for approximate glutamate levels in foods.
※This article is a general-audience science explainer. The figures given are approximations for understanding the underlying mechanism. The amount of any substance in food varies greatly by type, origin and ripeness. If you experience symptoms after eating, please consult a doctor.