His soldiers chewed on licorice root to conserve water, which was scarce. One of our projects involves investigating whether phytochemicals in citrus, soy and other foods bind to hydroxysteroid dehydrogenases, which could explain their hormonal activity. In addition, we are studying the binding of phytochemicals to steroid receptors. There is an evolutionary basis for the endocrine activities of phytochemicals in humans. Plants synthesize compounds that interfere with animal physiology as a defense against consumption by animals.
Some phytochemicals are hydrophobic and have cyclic structures similar to that of steroids.
The use of chemicals by plants as a defense against animals is ancient, originating well before the origin of humans. Because many human proteins, including steroid receptors and dehydrogenases, retain structures at their active sites that resemble their ancestral proteins in insects, fish, amphibia, etc., plant-derived compounds that evolved to act in these animals also have activity in humans. Similarly, some pesticides that are designed to interfere with insect physiology have structures that promote binding to human proteins, which can have profound effects on human physiology. Indeed, pesticides, plastics and other synthetic chemicals that have entered our food supply have been found to have hormonal activity. In particular, some of these compounds bind to the estrogen receptor.