Your Herbs are Trying to Kill You

The Dangerous and Seductive World of Phytochemicals

Among my many plant obsessions, growing and cooking with herbs and spices is one my favorite horticultural pastimes. Herbs are, after all, a bridge between two things I love: the garden and the kitchen. During this past winter, while confined to reading about gardening, my plant studies turned to ethnobotany, the study of the complex relationship of people and plants. What I read changed the way I look at those seemingly benign green lumps outside my kitchen.

First, I was struck by the awe and reverence that our ancestors had for these plants. From the earliest times, herbs and spices have been among the most highly prized and costly of ingredients. Entire empires rose and fell trying to control the trade of herbs and spices. Even before that, the religions of the ancient world viewed these plants as a means of spiritual fulfillment reached through sensuous experience (see Song of Solomon 4:12-15). Which prompts the question: was this infatuation and reverance just ancient superstition, or are these plants somehow powerful in mysterious ways?  In the last ten years, new studies of plant's phytochemicals offer some answers.

“Plants are virtuosos of biochemical invention,” writes food science writer Harold McGee. The chemicals in plants are potent stuff. That boring potted oregano on your patio is actually an arsenal of phytochemicals. To chew on a raw leaf of oregano is not pleasant, and that’s mostly due to the toxicity of the chemicals in the plant. In fact, the purified essence of oregano and thyme can be bought from chemical supply companies with warning labels on  them.  Surprisingly, that’s exactly the plant’s goal. While animals can use their mobility to avoid predators, stationary plants resort to chemical warfare. Each plant produces thousands of strong, sometimes poisonous chemicals to ward off animals, humans, bacteria, and insects.

Herbs and spices stockpile aroma chemicals in oil-storage cells connected to glands on the surface of the leaves. Though we think of herbs or spices having a single flavor, they often contain a mixture of several aromatic compounds combined. So when you smell coriander seed, for example, you smell both flowery and lemony; bay leaves mix eucalyptus, pine, and flowery aromas. The individual flavor chemicals are a fascinating study unto themselves: cineole is found in sage, basil, and nutmeg and gives these plants their characteristic freshness; the phytochemical estragole gives tarragon its anise flavor; and safrole gives both the herb hoja santa and the root of the sassafras tree (from which root beer is derived) its distinctive “candy-shop” aroma.

The great irony is that humans have come to love these very plants that mean to do us harm. We have even learned to enjoy chemicals that are designed to hurt us. Think of the pungent sulfuric compounds of onions and the allium family, or the burn of capsicums from peppers. Ginger, mustard, horseradish, wasabi--we convert these weapons into pleasure through breeding and cooking. Cooking dilutes the effect of the essential oils. We still ingest these toxins, but at lower levels because they are mixed with other foods.

So are these phytochemicals bad for us? Probably not in small doses. In fact, most herbs and spices contain phenolic compounds that are chock full of antioxidants which prevent DNA damage, cancers, and inflammation. But certain people should be careful. Pregnant women, in particular, should be cautious about ingesting certain herbs or spices, as some are feared to induce contractions. Developing fetuses may not have developed the immunity to the toxins of certain phytochemicals. So check with your doctor.

Science seems to confirm what our ancestors knew for centuries: that herbs and spices are seductive, yet powerful alchemists. I will never look at my potted oregano the same way again.