Phytochemicals are biologically-active compounds produced by plants. In fact, they're primarily what give the foods we eat their color. For example, phytochemicals are what make strawberries red and blueberries blue. However, these compounds also have an array of health benefits, including a reduction in the risk of major chronic diseases. That's largely because many of them act as antioxidants. Currently, there are about 5,000 known phytochemicals. The precise biological impact of most of them remains unclear, as only a few dozen have been studied in detail. Scientists also believe there are thousands more as-yet-unidentified phytochemicals. Only about 5% of known phytochemicals are absorbed directly. The rest are broken down, processed and metabolized in our gut by bacteria.