Milligrams (mg) vs. Fibrin Units (FU)

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​As a leading seller of enzyme supplements, a question that we often get is regarding systemic enzymes, in particular. Systemic enzymes are enzyme supplements that work throughout the body, or “systemically”, as a biocatalyst, speeding up the chemical reactions that make up our life. The human body contains nearly 3,000 enzymes, with functions ranging from anti-inflammatory and anti-fibrosis, to blood cleansing and virus fighting. Enzymes play a large role in digestion as well, but for the purposes of this article, we are focusing on systemic enzymes in particular.

​Typically, when you purchase your vitamins or other supplements, you look at the label and focus on the number of milligrams (mg) or grams (g) of each ingredient. These are quantitative measurements, showing us how much of “xyz” ingredient is in the product, and this is important because there are recommendations for how much of a particular vitamin or mineral that we as humans should consume on a daily basis. Enzymes are slightly different, however.

The most important measurement to pay attention to when it comes to enzymes is their potency, or biological activity. If you’ve bought a systemic enzyme supplement before, you’ve probably noticed the letters SU, SPU, FU, or IU somewhere on the product label. These letters are all used as a measurement of how active the enzymes are, and how well they will work when introduced to the body. So they are a measurement of quality, not quantity. Specific testing is conducted in order to determine these figures.

SPU and SU stand for Serrapeptase Units, and are used interchangeably between supplement brands when referring to the potency of the specific enzyme, serrapeptase. The best serrapeptase products will contain 100,000 units or higher per capsule.

FU stands for Fibrin Units, and is used for the enzyme, nattokinase. The standard for nattokinase manufacturing is a potency of 2,000 FU per capsule.

The IU designation stands for International Units, and is generally used when showing the potency of a blend of several different enzymes in a product, although FU can be used as well.

Again, all of these abbreviations are just different ways of disclosing the same thing…the "strength" of the enzymes on a per-serving basis. A systemic enzyme supplement with a higher potency will require a smaller dosage in order to produce the desired effect.
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When you see enzymes measured in milligrams on a product label, this is simply letting you know how much the enzyme weighs (ie. how much of the enzyme is actually in the formula). It is not telling you anything about the biological activity that it produces. You could have 200 mg of an enzyme that is of poor quality, and likewise, you could have 4,000 FU of an enzyme, but only have 50 mg of it in the formula.

​Using nattokinase as an example, some companies will use certain labeling techniques to make it appear as though there is a stronger form of nattokinase in the product, but when we do that math, we see that there is very little, if any difference.
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So, in addition to grams and milligrams, be sure to look for the units of activity (SU, SPU, FU, IU) on the label of an enzyme supplement. If you do not find one of these indicators, ask the manufacturer, or find a different product to use.
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