Enzyme activity units, explained
Two enzyme supplements can list the same number of milligrams and have very different real-world strength. That's because milligrams measure the weight of the enzyme protein, not how active it is. Activity units measure what the enzyme actually does — a functional test, not a weight measurement.
Why this matters for comparing products
A milligram of a weak enzyme preparation and a milligram of a highly purified, high-activity preparation can behave completely differently in the body. This is exactly why regulatory and industry standards (the Food Chemicals Codex, or FCC) define specific activity assays for each enzyme type — so a unit means the same thing regardless of which company printed the label.
Common units, and what they actually measure
- ALU (Acid Lactase Unit) — used for lactase. One FCC Acid Lactase Unit is the amount of enzyme that releases one micromole of a marker compound (o-nitrophenol) per minute, at 37°C and pH 4.5 — conditions chosen to mimic the acidic environment lactase typically works in in these products.
- GalU (Galactosidase Unit) — used for alpha-galactosidase, the enzyme in gas-relief products like Beano. Measured under the FCC method for this specific enzyme class.
- HUT (Hemoglobin Unit on a Tyrosine basis) — a common unit for protease, measuring how much a protease breaks down a standardized hemoglobin substrate.
- DU (Dextrinizing Units) — a common unit for amylase, measuring starch-breakdown activity.
- FIP (Fédération Internationale Pharmaceutique units) — commonly used for lipase activity.
Other enzymes (cellulase, invertase, phytase, and others) have their own FCC-defined units; the general principle is the same across all of them — the unit describes a standardized functional test, not a weight.
How to actually use this when comparing labels
When a product lists both a milligram amount and an activity unit for the same enzyme, the activity unit is the more meaningful number for comparing strength between products. If a label lists only milligrams with no activity unit at all, you have no reliable way to compare its real strength to a competitor — that's a real limitation of the label, not something we can estimate for you.
For price comparisons specifically, the most useful number is price per activity unit at the labeled serving size, not price per capsule or price per milligram — see our buying guide for how this fits into a full evaluation.
Sources: Enzyme Development Corporation, FCC specification sheet for FCC-IV Acid Lactase (β-galactosidase), defining the ALU assay; Food Chemicals Codex (FCC) enzyme activity assay methodology, industry-standard reference for GalU, HUT, DU, and FIP unit definitions.
Last reviewed: July 28, 2026.