Polyphenols are chemical substances that plants produce in order to survive in their surrounding environment, from which they cannot move. Although polyphenols are known to have beneficial physiological effects for humans, with antioxidant and anti-inflammatory properties, their mechanisms of action are, for the most part, a mystery. Their most reliably established property is their protective effect on blood vessels. Scientists say polyphenols act to prevent the onset of cardiovascular disease by curbing arteriosclerosis. If efforts to shed light on their effects progress, polyphenols might one day be classed as the “seventh nutrient,” alongside protein, fat, carbohydrates (also known as the three major nutrients), vitamins, minerals, and dietary fiber.