The Definition of Flavonoid
Over 9,000 individual flavonoid compounds have been identified and characterized in the plant kingdom, and countless others await future discovery. Flavonoids are ubiquitously found in the fruits and vegetables of your diet, as well as in spices, herbs and medicinal plants. Your body recognizes flavonoids as foreign compounds, and your body’s metabolic machinery is geared toward eliminating the flavonoids that you eat. Nevertheless, research indicates that your flavonoid intake may be inversely associated with your risk for developing cardiovascular diseases and cancer, and the flavonoids that you consume may even help you to lose weight.
Flavonoids are a sub-class of compounds called polyphenols. Chemically, a phenol consists of a six-carbon ring structure called benzene that has a hydroxyl, OH, group attached. Flavonoids characteristically are comprised of two phenol rings linked together. Most of the flavonoids in your diet are attached to simple sugars and called flavonoid glycosides, although some parent flavonoids called flavonoid aglycones are also present. Flavonoids are colored pigments, and they contribute to the hues and shades of yellow, red and blue of the leaves, stems and flowers of all plants.
Flavonoids are classified into several types according to the diversity of their unique structures. The major classes of flavonoids are called flavonols, flavones, flavanones, flavanols or catechins, anthocyanidins, isoflavones and chalcones. Soybeans are a good source of isoflavones, berry fruits and cereal grains contain a high level of anthocyanidins and teas are rich in catechins. The flavonol quercetin and the flavone apigenin are present in many fruits and vegetables, including onions, apples, broccoli and berries, and naringenin is a citrus flavanone. Xanthohumol is a chalcone from the hop plant, and significant levels may be found in microbrewed beers.
Flavonoids are Xenobiotics
Flavonoids are considered to be xenobiotics, or foreign compounds that are preferentially eliminated from your body through your urine or bile after they are absorbed. Flavonoid glycosides may be directly absorbed through your intestinal cells and enter your blood, or they may be broken down by intestinal bacteria to the aglycone forms, which are also absorbed. In the cells of your intestinal wall, as well as in your liver and other tissues, flavonoids are attached or conjugated to compounds that make the flavonoids more water-soluble to facilitate their excretion.
Within your body's cells, flavonoids can uniquely bind to proteins, and therefore, they can produce a variety of biological effects. For example, flavonoids are known to have anti-inflammatory properties, and they may correct cell-signaling abnormalities that are associated with cancer development. Additionally, flavonoids can improve the elasticity of your artery walls and lower your blood pressure. Finally, flavonoids stimulate the breakdown of triglycerides in your fat cells and the burning of fat in your liver, and flavonoids may help to maintain your blood glucose at an optimal level.
- Mini Reviews in Medicinal Chemistry: Polyphenols and Cardiovascular Disease – A Critical Summary of the Evidence
- Recent Patents on Inflammation and Allergy Drug Discovery: Dietary Flavonoids – Molecular Mechanisms of Action as Anti-Inflammatory Agents
- Frontiers in Bioscience (Scholar Edition): Dietary Flavonoids as Cancer-Preventive and Therapeutic Biofactors
- Nutrients: Dietary Polyphenols and Obesity
- Mini Reviews in Medicinal Chemistry: Flavonoids Health Benefits and Their Molecular Mechanism
- USDA Database for the Flavonoid Content of Selected Foods, Release 3 (2011)
- USDA Database for the Isoflavone Content of Selected Foods, Release 2.0
- Flavonoids – Biosynthesis, Biological Effects and Dietary Sources; Raymond B. Keller
- Flavonoids – Chemistry, Biochemistry and Applications; Oyvind M. Andersen and Kenneth R. Markham
Michael Peluso is a semi-retired scientist in the field of nutritional biochemistry. He received his M.S. in nutrition from the University of California, Davis and Ph.D. in nutrition from the University of Missouri. Peluso's work has appeared in scholarly publications such as the "Journal of Nutrition," "Lipids" and "Experimental Biology and Medicine."