Nattokinase, explained from scratch: everything to know before your first bottle

Start at zero: what is natto?

Natto is a food. Not a pill, not an extract — breakfast.

It's whole soybeans that have been fermented by a specific bacterium until they turn brown, soft, and profoundly sticky. In Japan it's eaten in the morning, usually over hot rice, often with mustard and a little soy sauce. It has been on Japanese tables for roughly a thousand years, long before anyone knew there was an enzyme in it.

We should be honest about it, because everyone else is coy: natto is polarising. It smells sharply of ammonia and old cheese. When you lift it with chopsticks it pulls dozens of fine sticky threads that stretch and refuse to snap. Plenty of Japanese people won't touch it. Plenty of people who grew up on it eat it every single morning without thinking about it once.

Those threads aren't slime or spoilage, by the way. They're a chain of glutamic acid — a natural polymer the bacteria build as they work. Stickiness is the sign the ferment went right.

How natto is actually made

It's four steps, and it hasn't meaningfully changed in centuries. Traditionally the beans were wrapped in rice straw, which carried the bacteria naturally. Today the culture is added deliberately, which is why modern natto is consistent instead of a gamble.

That third step is the one that matters. The soybean doesn't contain nattokinase. The bacterium makes it. As Bacillus subtilis natto digests the beans, it secretes a set of enzymes — and one of them is the one this whole industry is built on.

Which means nattokinase isn't really a "soy supplement." It's a bacterial enzyme that happens to be produced in a soy food.

The 1980 accident that found the enzyme

For a thousand years natto was just food. Then a Japanese researcher named Dr. Hiroyuki Sumi, working at the University of Chicago Medical School, went looking for something else entirely.

Sumi was screening foods for enzymes that could break down fibrin — the stringy protein the body uses to knit things together. He went through more than 170 different natural foods, one after another, and got nothing worth writing about.

Then, in 1980, he dropped a bit of natto onto a dish of fibrin and left it at body temperature. When he came back, the fibrin had dissolved.

He had tested 173 foods. The one that worked was the breakfast he'd grown up with.

He named the enzyme nattokinase — literally "the enzyme in natto" — and published the work in 1986. It was the first enzyme of its kind ever documented in a food rather than in a laboratory or a venom. That paper is the reason this ingredient exists on shelves at all.

What nattokinase does — and what it doesn't

Here's the honest version, which is shorter and duller than what you'll read elsewhere.

What it's for

Nattokinase supports healthy circulation, and supports a healthy heart. Circulation is the least glamorous system you own — it's just the delivery network, moving everything your body runs on out to your hands, your legs and your head, every second, without ever asking you for attention. Most people have never once thought about it. That's the whole pitch, and it's the only mechanical claim on this page.

What it is not

It is not a drug. It has not been approved to treat, cure, or prevent anything. Any effects in the published human research are modest — this is a supplement operating over months, not a pill that does something dramatic on a Tuesday.

So when you see a nattokinase ad promising it clears, dissolves, flushes or reverses something in your body — plaque, cholesterol, arteries, clots — you're looking at someone breaking the law, not someone with better science. Those claims are illegal for a supplement to make, and the fact that they're everywhere in this category should tell you what kind of category it is.

FU vs mg: the only number that matters

This is the part nobody explains, and it's the part that decides whether the bottle in your hand is worth anything.

Nattokinase is an enzyme. An enzyme isn't a substance you need a certain weight of — it's a machine that does a job. What matters is whether the machines still work. Enzymes get damaged by heat, by time, by rough processing. A capsule can be full of dead enzyme.

Milligrams measure the wrong thing

Milligrams tell you the weight of powder in the capsule. That's it. It's the number on the front of most bottles because it's a big impressive-looking figure that costs nothing to be true.

FU measures the actual work

FU stands for fibrinolytic units. It's an activity measurement, not a weight one: the enzyme is put onto a fibrin plate under standardised conditions, and how much it does is measured directly. One FU is a defined amount of that activity. The scale was standardised in Japan and it's what the human research is dosed in.

Two bottles can both say "100 mg of nattokinase" and deliver completely different amounts of working enzyme.

If a nattokinase bottle doesn't print an FU number where you can find it, that isn't an oversight. It's the answer.

How much do people actually take?

Once you know to look at FU, the market sorts itself into a few obvious tiers. Here's the landscape you're shopping in:

There's no official recommended dose — it's a supplement, not a prescription, and nobody has set one. What we can tell you is that the tiers are real, the difference between them is real, and a lot of shoppers buy the 2,000 assuming a bottle is a bottle.

More isn't automatically better in supplements, and we're not going to pretend otherwise. But it is the difference between knowing what you bought and guessing.

Can't I just eat natto?

Honestly? Yes. If you'll eat it, eat it.

We sell a supplement and we're still going to say that, because it's true and you'd find out anyway. Natto is a whole food. It brings fibre, protein and vitamin K2 along with the enzyme. Millions of people have done exactly this for a thousand years without a single capsule.

Here's the catch, and it's the only reason this industry exists:

• Most people won't eat it. The smell and the texture end the conversation for the large majority of Westerners who try it once.
• You don't know what you're getting. A tub of natto has no FU printed on it. Enzyme content swings with the strain, the ferment, and how long it's sat there.
• Heat is the enemy. Enzymes don't survive cooking well. Natto stirred into a hot dish is a different proposition than natto eaten cold.
• Availability. If you don't live near a Japanese grocer, you're ordering frozen tubs and hoping.

So the supplement isn't better than the food. It's the version you'll actually take every morning for a year — which is the only version that does anything at all.

How to judge any nattokinase bottle in 30 seconds

Take this to any shelf or any search results page. It works on ours too — that's the point. The last column is for the bottle you're actually considering.

Who should not take it

Most brands bury this at the bottom in grey six-point type. It belongs here, before you spend anything — because nattokinase is genuinely biologically active, and that's precisely why it isn't for everyone.

If you take any prescription medication, ask your doctor before you start — genuinely, not as a formality. We would rather lose a sale than have you guess about this.

Where Genki fits

You now know more about nattokinase than most people selling it. Here's ours, measured against the checklist above — check it yourself.

The number is on the front

10,000 FU per serving, printed in the largest type on the label — not on the back, not in a footnote. It's the first thing you can check and the easiest thing to compare.

Nothing hides behind "proprietary"

Alongside the nattokinase, every serving carries:

• CoQ10 — a compound your body already makes, concentrated in its hardest-working tissue.
• Bromelain — an enzyme from pineapple, long paired with nattokinase.
• Turmeric — the kitchen staple that earned its way into the supplement aisle.
• Aged garlic extract — long used in traditional practice, and aged so you're not wearing it all day.
• Pine bark extract — the ingredient that's been studied alongside nattokinase for circulation in the legs, which is where a day at a desk tends to show up first.

Each one is named on the front of the label, in plain English.

Eighty days, and thirty to change your mind

240 vegetarian capsules is roughly an 80-day supply, so you're not re-ordering every three weeks. For how much to take and when, follow the serving directions on the label — natto has always been a breakfast food, and most people find that rhythm easiest to keep.

Circulation isn't a light switch. Nobody honest will tell you you'll feel something on day three. So take it for a month, and if you don't want to keep going — for any reason, or none — we refund it. Thirty days, money back.

That's the whole offer. We'd rather the guarantee did the persuading than a countdown clock.

Questions people actually ask