Nattokinase: The Enzyme from Natto, Explained Simply

Picture a Japanese breakfast: on top of steaming rice sits a sticky, stringy soybean dish that makes even some Japanese people wrinkle their noses. It's from this exact dish – natto – that one of the most discussed enzymes in the supplement world comes: nattokinase. If you're searching for this term, you probably want a clear answer to two questions: what exactly is this enzyme, and what do I need to watch out for?

In short: nattokinase is a protein-splitting enzyme (protease) produced by the bacterium Bacillus subtilis natto during the fermentation of soybeans into natto. In the lab, it's fibrinolytically active – meaning it can break down the protein fibrin – and is dosed not in milligrams but in enzyme units (FU, fibrinolytic units). No health claims are currently approved in the EU for nattokinase; anyone taking blood thinners or planning surgery should be sure to check with a doctor before taking it.

The Essentials at a Glance

• What: an enzyme from fermented natto, produced by Bacillus subtilis natto.
• Type: a protease (protein-splitting), fibrinolytically active in the lab.
• Dosage: measured in FU (fibrinolytic units) – not simply in mg.
• Form: almost always enteric-coated capsules, to protect the sensitive enzyme.
• Caution: be sure to check with a doctor if you take blood thinners, have a clotting disorder, are planning surgery, or are pregnant or breastfeeding.

What Is Nattokinase – and Where Does It Come From?

Natto is one of Japan's oldest fermentation traditions: steamed soybeans are inoculated with the bacterium Bacillus subtilis natto and left to ripen until the characteristic sticky, stringy texture develops. During this fermentation, the bacterium produces a whole bundle of metabolic products – including the enzyme that was isolated by a Japanese researcher in the 1980s and named "nattokinase" for its fibrin-dissolving property.

For supplements, the enzyme is extracted from the fermentation and purified – without the intense, ammonia-like smell and the tough strings that make real natto inaccessible to many Western palates. Important to understand: nattokinase is not natto. It's a single, specifically isolated enzyme from this food – not a whole soy product. For an overview of related protein-splitting enzymes, see our guide Digestive enzymes: an overview.

How an Enzyme Works in the Body

Enzymes are proteins that act as biological "tools," speeding up chemical reactions without being used up themselves. Each enzyme fits a specific target molecule according to a lock-and-key principle. In nattokinase's case, this target – in the test tube – is the fibrous protein fibrin, the protein the body produces to make blood clot. It's precisely this lab-measurable fibrinolytic activity that makes nattokinase interesting for research – and, at the same time, delicate for people on blood-thinning medication.

A clean distinction is worth making here: an enzyme activity measurable in the lab is, first and foremost, a chemical property in a test tube – not proof of a specific effect in the human body. This honest distinction is exactly the crux of the matter with nattokinase.

FU, Not mg: The Crucial Unit of Measurement

One particularity you should definitely know: with nattokinase, a plain milligram figure says little about the actual enzyme activity. Two products both labeled "100 mg" can have completely different levels of activity. That's why nattokinase is stated in FU (fibrinolytic units) – a measure of the enzymatic activity itself.

A reputable product states the FU figure transparently. If it's missing and only an mg figure appears on the label, the quality can hardly be assessed. How to read a label properly shows you how to decode such figures in general.

Why People Use Nattokinase

In Japan, natto has been part of the traditional diet for centuries, especially in the Tokyo region, where it's classically eaten over rice at breakfast. Nattokinase as an isolated enzyme, by contrast, is a modern product of enzyme research. People who use it usually do so out of interest in a well-characterized enzyme from fermented food – often in the context of much-discussed cardiovascular topics. A neutral framing matters here: interest in a topic is not a promise of effect.

Fermented foods are generally having a comeback – from kimchi to kombucha to probiotic cultures. Natto fits into this tradition and, as the raw material for nattokinase, has additionally sparked scientific interest.

What Research Is Looking Into

Nattokinase is well characterized in the lab – its fibrinolytic activity is an established feature for study. Research is interested in how the enzyme behaves in the test tube, how it's metabolized, and what role its enzymatic activity plays. A recurring theme is its connection to the cardiovascular system, which is why nattokinase keeps coming up in this line of research.

One fascinating open question concerns absorption: nattokinase is a large protein molecule, and proteins are normally broken down into their building blocks in the digestive tract. Whether and to what extent the intact enzyme makes its way from the gut into circulation is scientifically debated – and is also the reason why almost all products rely on the enteric-coated capsule.

Honestly assessed: a large part of the evidence comes from laboratory work and smaller studies. Large, robust human studies for specific goals are limited, and the evidence isn't conclusive. The research direction is interesting – but no health promise can be derived from it, and we deliberately don't make one.

Approved Claims: The Honest Status

No health claims are currently approved for nattokinase itself in the EU under the Health Claims Regulation. We therefore describe the enzyme factually and neutrally – its origin, its properties as a protease, dosing in FU, and the state of research, without any promise of effect. This honesty is deliberate: it's what distinguishes a trustworthy product from sensationalist marketing.

Forms, Quality, and Use

Nattokinase is usually offered in enteric-coated capsules. The reason: enzymes are sensitive to stomach acid, and a protective capsule coating is meant to carry the enzyme through to the small intestine. When buying, it's worth checking several points:

• FU figure: stated transparently and per capsule – the most important quality signal.
• The vitamin K2 question: some extracts are specifically stripped of vitamin K2, so that the effect of blood thinners isn't influenced – an important detail if you're on such medication. Background in Vitamin K and blood clotting.
• Purity & lab testing: see lab-tested explained.
• Storage: cool and dry – enzymes are sensitive, see Shelf life and storage.

Whether it's better to take nattokinase on an empty stomach or with food depends on the product – for general guidance, see taking supplements on an empty stomach, explained. For using supplements wisely in general, common mistakes with supplements offers guidance.

Who Needs to Be Especially Cautious?

Because nattokinase is a fibrinolytically active enzyme, particular caution is warranted here. Anyone taking blood-thinning medication (e.g., anticoagulants), living with a clotting disorder, or planning surgery or a dental procedure should never take nattokinase without prior medical consultation. The same applies during pregnancy and breastfeeding, and with existing cardiovascular conditions. For persistent symptoms, please see a doctor. More on the interplay with medications can be found in Supplements and medications.

Honestly Assessed

What's certain: nattokinase is a well-characterized, fibrinolytically active enzyme from traditionally fermented natto, dosed in FU. What's open: robust evidence of effects in humans for specific goals is limited, and the absorption of the intact enzyme is still debated. Because of the enzyme's properties, medical clearance with certain medications isn't a nice-to-have here but genuinely important – that's exactly what responsible use of this enzyme looks like.

Matching Products from Scheunengut

You'll find nattokinase at Scheunengut in our Enzymes and Heart & Circulation categories. If enzymes interest you more broadly, it's also worth looking at other protein-splitting enzymes such as serrapeptase and bromelain from pineapple. On the heart topic, see also Nutrients for heart and circulation, Omega-3 and the heart, and Nutrients for normal blood vessels.

Frequently Asked Questions (FAQ)

Is nattokinase the same as natto?

No. Natto is the complete fermented soy dish, containing protein, fiber, and vitamins. Nattokinase, by contrast, is just a single enzyme that forms during fermentation and is isolated and purified for the capsule – odor- and taste-neutral, without the tough strings.

What does the FU figure mean for nattokinase?

FU stands for fibrinolytic units and measures the enzymatic activity – in other words, how active the enzyme is. Because two products with the same mg figure can have very different levels of activity, the FU figure per capsule is the number that actually matters. If it's missing from the label, the quality can hardly be assessed.

Why are nattokinase capsules enteric-coated?

Enzymes are proteins and react sensitively to stomach acid. An enteric coating is meant to carry the enzyme unharmed through the stomach and into the small intestine. This is also one reason why the absorption of this large enzyme molecule is discussed in research.

Who shouldn't take nattokinase without medical consultation?

Anyone taking blood-thinning medication, living with a clotting disorder, or planning surgery or a dental procedure should only take nattokinase after medical clearance. The same applies during pregnancy and breastfeeding, and with cardiovascular conditions. For persistent symptoms, please see a doctor.