Phenolic compounds found in plants are believed to be effective in prevention of oxidative stress related diseases. An interest in antioxidants and natural foods continues to grow along with a commercial interest in plant-derived phenolic products. Flavonoids represent a family of plant compounds high in phenolic related antioxidant activity. They are poorly absorbed in the body. Many published studies show the antioxidant activity of the flavonoid, but fail to consider the activity of the metabolite which is actually bioavailable to the body. The paper concludes that there remains a need to develop adequate physiological models supporting antioxidant activity of polyphenols.