Milk thistle is a member of the aster family that is native to southern Europe and Asia and now naturalized throughout much of the world. Like most thistles, milk thistle is characterized by sharp spines or thorns that surround the flower head. While the seeds are most frequently used to make teas, tinctures and infusions, they can also be as food. In fact, the seeds, with a flavor profile similar to flax, contain up to 25% protein. Try adding whole milk thistle seeds to salads, shakes and smoothies, cereals and breads.

Milk thistle seeds contain several active chemicals, including a group of closely related flavonolignans. Collectively known as silymarin, the group consists of silybin A, silybin B, isosilybin A, isosilybin B, silychristin, isosilychristin and silydianin. The raw seeds contain about 6% of this flavonolignan complex, while the liquid extract prepared from the seeds contains as much as 80%.