One of the most important groups of phytonutrients and antioxidants is the flavonoids. There are more than four thousand flavonoids in the diet, mostly found in fruits, vegetables, herbs, and spices. The flavonoids provide the dark color to the skin of vegetables and fruits, such as the color of red onions. Americans consume about one-fifth the amount of flavonoids as Asians, explaining in part the lower incidence of cancer and heart disease in people with traditional Asian diets compared to Americans. Total flavonoid intake is inversely related to the incidence of heart disease.  

The primary sources of flavonoids in the diet

The flavonoids include catechinsfrom green tea, polyphenols from red grape skin (which protect against heart disease), and quercetin, a potent antioxidant in grapefruits that helps regenerate vitamin C. Foods richest in flavonoids include: 

• Legumes

• Green tea

• Cherries

• Blueberries

• Raspberries

• Red grapes

• Beets

• Asparagus

• Onions

• Sweet potatoes

• Spices such as ginger, parsley, sage, and turmeric (as well as many Chinese and Ayurvedic herbal remedies)  

Other potent members of the flavonoid group include rutin in buckwheat, hesperidin in citrus fruits, silymarin in milk thistle, genistein in soybeans, apigenin in chamomile, and resveratrol in red grapes and wine.

Detoxifying the body with green tea

A superstar of the flavonoids is green tea, produced by lightly steaming the leaves of the tea plant (Camellia sinensis). Polyphenols, the biologically active compounds in teas, are partially deactivated when tea is oxidized, as in black tea. The polyphenols in green tea include catechin, proanthocyanadins, and epigallocatechin, considered the most active flavonoid in tea.

Green tea polyphenols have shown higher antioxidant activity than vitamin C and vitamin E. Green tea can also increase the activity of detoxifying enzymes, including glutathione and catalase, active in the liver, lungs, and small intestine. Green tea activates both Phase I and Phase II of detoxification.

Connections between green tea and cancer risk

Green tea consumption has been linked to the reduced incidence of many cancers, including stomach, small intestine, bladder, prostate, skin, pancreas, colon, breast, and lung. The lower incidence of cancer in Japan might be explained at least in part by green tea consumption. One of the effects of green tea is to normalize gene expression, reducing cancerous cellular changes. (See Chapter 9 of The Adaptation Diet for more information on the epigenetic effect of green tea.) Green tea appears to inhibit estrogen’s stimulation of breast receptors in estrogen-sensitive cancers. Additionally, green tea suppresses the activation of carcinogens, detoxifies carcinogens, and inhibits nitrosamine production from foods such as bacon, hot dogs, ham, and other processed meat.

In most studies, green tea consumption was four to ten cups per day. Each cup contains an average of 80–120 milligrams of polyphenols. Green tea extracts can be used that contain 300 to 600 milligrams of polyphenols standardized to contain 80 percent polyphenols and 55 percent epigallocatechin. To reach the possible benefit found in population studies, a minimum of 300 milligrams should be taken as a supplement.

Broad-based benefits of blueberries

Studies have shown remarkable properties in another underutilized food, wild blueberries. In animal studies, Papandreou and colleagues (2009) found that rats fed wild blueberries had better memory for spatial tasks and improved coordination. During World War II, British pilots ate wild blueberries to improve their night vision and coordination. Blueberries contain high amounts of polyphenols that give the berries their blue color and tartness. These chemicals have been shown to be strong antioxidants that are cardioprotective, improve circulation, inhibit certain cancers, and protect against age-related cognitive dysfunction and motor deficits. It appears that the more tart wild blueberry has a higher concentration of these polyphenols than those commercially produced. In either case, these studies show the benefit of eating a wide variety of fruits and vegetables, especially those with intense coloration, including pomegranate, raspberries, blackberries, and red grapes.

The potent properties of quercetin

Quercetin, found in a wide range of foods, including red onions, grape skins, green tea, and tomatoes, is one of the most potent flavonoids and has been shown to protect against the development of diabetic complications such as diabetic cataracts, neuropathy, and retinopathy. Quercetin can possibly lower cardiovascular risk, lower cholesterol, and improve endothelial function. In a study by Kleemann and colleagues (2011), quercetin was found to lower arterial inflammation and an important marker of heart disease risk, C-reactive protein (CRP). Quercetin also appears to have potent antiviral properties (as do most of the flavonoids), with inhibition of viral infections including herpes type 1, parainfluenza, polio, and respiratory syncytial virus. Quercetin might also have some benefit in treating the common cold. The recommended daily dosage as a supplement is 200–400 milligrams taken twenty minutes before a meal. It is also helpful to take bromelain, a digestive enzyme from pineapple, with the quercetin to enhance its anti-inflammatory effect.

Promoting healthy skin with proanthocyanadins

Proanthocyanadins, which are found in grape seeds, red wine, and commercial extracts from maritime pine bark, have potent antioxidant and anti-inflammatory effects. They prevent damage to collagen, the protein that constitutes much of the connective tissue, tendons, and ligaments. These potent antioxidants have fifty times the effect of vitamin C in protecting connective tissue and can reduce symptoms from arthritis and allergies, lower cholesterol, strengthen capillaries, and promote healthy skin.

If you’d like to learn more about the benefits of incorporating flavonoids into your diet (or The Adaptation Diet in general), please call us and set up an appointment. Whether you’re interested in living a healthier lifestyle or you’re trying to overcome a chronic condition, we can help you get to your goals.