How much protein is in milk thistle?

There's no published protein figure for milk thistle seed, the part actually used in supplements. The closest available data — a 2025 lab analysis of the plant's stems, leaves and flowers — found about 10% protein in the flowers, but flowers aren't what's sold as a supplement, so that number doesn't answer the seed question directly. Either way, a typical capsule serving is too small for the protein content to matter.

No data on the part that's actually sold

Milk thistle supplements are made from the seed — pressed, ground, or extracted into standardized silymarin. No standard food-composition database, including USDA FoodData Central, has a published protein figure for milk thistle seed. A 2025 laboratory study did analyze the plant's nutritional composition, but it tested the stems, leaves and flowers, not the seed — finding roughly 5% lipid, 70% carbohydrate and 10% protein by weight in the flowers, with different figures for stems and leaves. Seeds and flowers typically have different macronutrient profiles in most plants, so this figure is informative about the plant generally but doesn't stand in for a seed-specific number.

Why it wouldn't matter much regardless

Even a firm seed-protein percentage wouldn't translate into a meaningful protein dose. A typical milk thistle capsule holds somewhere between about 150 mg and 500 mg of extract or seed material — compare that with a whey protein serving, which delivers protein in the tens of grams. At milk thistle's typical serving size, even a generous protein percentage would add up to a fraction of a gram, not a nutritionally relevant amount. Milk thistle isn't studied or marketed as a protein source; its research is entirely about silymarin's effect on liver and kidney markers, covered in milk thistle benefits: what the research does and doesn't show.

Questions people ask

Does milk thistle have protein in it?

The seed used in supplements hasn't been analyzed for protein content in any published database. A separate 2025 study found about 10% protein in the plant's flowers, but that's a different part of the plant.

Is milk thistle a good protein source?

No — even with a favorable percentage, a typical 150–500 mg capsule serving is far too small to contribute meaningfully to daily protein intake. Milk thistle isn't studied or marketed for that purpose.

Related reading: how much milk thistle should you take a day and what is milk thistle. For an actual protein source, see whey protein benefits: what the research does and doesn't show.