What “standardised to 20%” means on a label

A herbal supplement label usually carries two numbers: how many milligrams of extract are in the dose, and what percentage it is standardised to. The first is weight. The second tells you what is actually inside that weight.

What an extract is

An extract is a concentrate obtained from plant material using a solvent. The active compounds in a plant are a small fraction of its total mass — the rest is fibre, starch, pigments and water. Extraction concentrates the interesting part, but never isolates it completely.

So “500 mg of green tea extract” is not, by itself, information. Those 500 mg might contain 25 mg of catechins or 250 mg. The weight is the same either way.

What the percentage means

Standardisation is the guaranteed minimum share of a specific compound in the extract. “50% EGCG” means half the mass of the extract is epigallocatechin gallate. From 110 mg of such an extract you get 55 mg of EGCG.

The arithmetic is a straight proportion:

• extract amount × percentage = amount of active compound
• 110 mg × 50% = 55 mg EGCG
• 60 mg × 50% = 30 mg synephrine

If the percentage is missing from the label, that calculation cannot be made. Which is also why a manufacturer prints it when there is something to show.

An example: white kidney bean

White kidney bean extract (Phaseolus vulgaris) is standardised to phaseolamin. The commonly sold market grade is declared at 2% phaseolamin. Ours is 20%.

At equal weight, that is a tenfold difference in phaseolamin content. The illustration at the top of this article puts both figures on the same scale.

How to check

Open a label and look for three things next to each other:

• the Latin name of the plant and which part is used — root, bark, leaf, fruit
• the weight of the extract in milligrams per recommended daily dose
• the percentage, and which compound it refers to

If one of the three is missing, the other two are not enough to compare two products.

What the percentage does not tell you

Standardisation describes composition, not effect. It lets you compare two labels against each other, and nothing more. A high percentage does not turn a supplement into a medicine — food supplements do not treat or prevent disease and are intended to complement a normal diet.