What Does FU Mean in Nattokinase?

If you've compared nattokinase supplements, you've probably seen numbers such as 2,000 FU, 4,000 FU, 10,000 FU or 20,000 FU.

FU stands for Fibrinolytic Units.

FU is a measurement used to express the fibrinolytic enzyme activity of nattokinase. It is fundamentally different from milligrams (mg), which measure weight.

Understanding this distinction is important when comparing nattokinase ingredients and products.

What Are Fibrinolytic Units?

Fibrinolytic Units describe enzyme activity measured using an analytical assay.

Nattokinase is an enzyme associated with natto, the traditional Japanese fermented soybean food produced through fermentation involving Bacillus subtilis var. natto.

Because nattokinase is an enzyme, simply knowing the weight of a nattokinase preparation does not necessarily tell you its measured enzymatic activity.

That is why nattokinase is commonly characterized using FU in addition to, or instead of, weight alone.

FU vs Milligrams

Milligrams (mg) measure weight.

Fibrinolytic Units (FU) measure enzyme activity under specified assay conditions.

They therefore answer two different questions.

Milligrams answer:

How much material is present?

FU answer:

How much measured fibrinolytic activity does the material provide under the applicable assay?

This distinction means two nattokinase ingredients of identical weight can potentially have different activity specifications.

Example: 100 mg Does Not Always Mean the Same FU

Consider two hypothetical nattokinase preparations:

Preparation A

100 mg
2,000 FU

Preparation B

100 mg
10,000 FU

Both preparations contain 100 mg by weight.

However, their stated enzyme activities are different.

The opposite can also occur. Different quantities of two nattokinase ingredients can potentially provide the same FU if their activity concentrations differ.

Therefore, nattokinase products should not be compared using milligrams alone.

Understanding FU Per Gram

Bulk nattokinase ingredients are often characterized by their activity concentration.

For example, suppose a nattokinase ingredient is standardized to:

20,000 FU per gram

Because:

1 gram = 1,000 milligrams

the mathematical activity concentration would be:

20 FU per milligram

Therefore:

100 mg × 20 FU/mg = 2,000 FU

500 mg × 20 FU/mg = 10,000 FU

1,000 mg × 20 FU/mg = 20,000 FU

These calculations describe the relationship between the ingredient's stated activity concentration and the amount used.

They do not independently verify that a particular lot actually meets its specification.

Analytical testing is required for that determination.

What Does 10,000 FU Mean?

A label stating 10,000 FU per serving is describing the stated fibrinolytic enzyme activity supplied by that serving according to the applicable specification and assay.

It does NOT mean:

10,000 mg of nattokinase.

FU and mg are different measurements and should not be used interchangeably.

Likewise, a higher FU number describes higher measured enzyme activity under the applicable assay conditions. It should not automatically be interpreted as proof of superior overall product quality or a particular clinical outcome.

Is Higher FU Always Better?

Not necessarily.

FU tells you something important about enzyme activity, but it does not answer every question about a nattokinase product.

Product evaluation can also include:

• ingredient identity

• source material

• manufacturing process

• fermentation process

• activity specification

• analytical testing

• lot consistency

• microbiological specifications

• contaminants testing

• formulation

• serving size

• storage conditions

• packaging

Therefore, FU is an activity measurement, not a universal quality score.

How Is FU Verified?

Manufacturers and ingredient suppliers can use analytical testing to determine whether a nattokinase ingredient meets its stated activity specification.

Documentation may be provided through a Certificate of Analysis (COA) associated with a particular production lot.

Depending on the supplier and testing program, a COA may report information such as:

• product or ingredient identity

• lot number

• activity specification

• activity test result

• analytical method

• microbiological results

• applicable contaminant or purity testing

Consumers and professional buyers should distinguish between a marketing statement about potency and analytical documentation supporting an ingredient specification.

FU and the Certificate of Analysis

Suppose an ingredient is marketed as:

100,000 FU per gram

That is the ingredient's stated activity specification.

A corresponding lot-specific COA can provide evidence concerning whether the tested production lot met the applicable specification.

This distinction is particularly important for professional buyers, formulators and practitioners evaluating enzyme ingredients.

Why FU Matters When Comparing Nattokinase

Imagine Product A lists:

100 mg nattokinase

while Product B lists:

2,000 FU nattokinase

Those numbers cannot be directly compared without additional information.

To properly compare the products, you would want to know the activity of Product A.

Likewise, knowing only an FU value does not necessarily provide every detail concerning ingredient weight, formulation or overall product quality.

The most informative labeling provides sufficient information to understand the amount and activity of the enzyme preparation.

FU Does Not Equal Clinical Efficacy

This distinction is important.

FU is an analytical measure of fibrinolytic enzyme activity.

It is not, by itself, evidence that a particular serving prevents or treats a disease.

Laboratory enzyme activity, ingredient specifications and clinical outcomes represent different types of information.

Clinical conclusions require appropriate clinical evidence.

Frequently Asked Questions

What does FU stand for?

FU stands for Fibrinolytic Units.

Is FU the same as mg?

No.

Milligrams measure weight. FU measure fibrinolytic enzyme activity under specified assay conditions.

Does 10,000 FU mean 10,000 mg?

No.

FU is an activity measurement, while mg is a measurement of mass.

Can nattokinase have different FU concentrations?

Yes. Nattokinase preparations can be manufactured or standardized to different activity concentrations.

Can I determine FU from milligrams?

Only if you know the activity concentration of the specific nattokinase ingredient.

For example, if an ingredient is standardized to 20,000 FU per gram, its stated activity concentration corresponds mathematically to 20 FU per milligram.

Without knowing the activity specification, milligrams alone cannot tell you the FU.

Is higher FU proof of higher quality?

No.

Higher FU indicates higher measured fibrinolytic activity under the applicable assay conditions. Overall quality involves additional considerations including identity, manufacturing, testing, purity, consistency and formulation.

The Bottom Line

FU stands for Fibrinolytic Units and is used to express the measured fibrinolytic activity of nattokinase.

The key distinction is simple:

mg = weight

FU = measured enzyme activity

Understanding both measurements makes it easier to evaluate nattokinase ingredient specifications and compare products accurately.

Continue Learning

For a deeper explanation of how enzyme weight differs from enzyme activity, read Enzyme Potency Explained: Milligrams vs Activity Units.

Disclaimer

This information is provided for educational purposes and is not intended to diagnose, treat, cure, or prevent any disease. Enzyme activity measurements should not be interpreted as evidence of a particular clinical outcome.