Updated: Mar 11, 2021
Flavonoids are a group of phytochemicals found in plant sources and are one of the reasons why eating fruit and vegetables are so good for you. There are six major subclasses of flavonoids: anthocyanidins, flavan-3-ols, flavonols (most abundant), flavanones, flavones and isoflavones in the human diet (3).
The term anti-oxidant is likely to be familiar to you but we tend to think of the usual suspects like vitamin C, beta carotene and vitamin E. Over the last couple of decades there has been growing interest in a smaller group of compounds called flavonoids, of which over 5000 have now been identified (2).
These naturally occurring plant pigments fulfil a similar role in the diet by mopping up free radicals and reducing inflammation, but they also have other effects which go beyond the average anti-oxidant including anti-histamine, anti-microbial, anti-viral, estrogenic (4) and even anti-anxiety and mood enhancing properties (1). Together with carotenes, they are also responsible for the colouring of fruits, vegetables and herbs.
The flavonoid quercetin (apples, red onions, red wine) has anti-histamine properties and have been shown to be beneficial in the reduction of asthmatic attacks and assisting healing from acid reflux, eczema and sinus conditions (4) and have also shown benefits in improving endothelial function and metabolic (anti-diabetic) response (14).
A flavonoid called Epigallocatechin gallate (ECGC), found in green tea, has been shown in numerous studies to have anti-carcinogenic, tumour suppressing and anti-inflammatory properties. It's estrogenic modulation effects have been linked to the treatment and prevention of the development of Alzheimer’s due to the maturation of a compound (ADAM10) and it's relationship to declining estrogen and estrogenic receptors in the brain (9). ECGC also seems to reduce an activating immune compound called HMGB1, which in preliminary trials appears to shows promise in the survival rate of those with severe sepsis (7). It has even shown promise for those on a weight loss program, helping to reduce food intake, overall weight and fat composition, lowering of insulin and leptin and sex hormones like oestrogen (estradial) and testosterone – all beneficial as well in the support for hormonal cancers (10). Incredibly, ECGC can have as much as 100 times more anti-oxidant power than vitamin C. To maximise nutrient intake it is important to remember that to get the most from our diet it is not only what we eat but when we eat, so to ensure you get the most benefit from green tea avoid drinking it close to iron rich meals. This prevents binding with the iron and therefore maintains the beneficial compounds from the tea (8). Iron rich foods include green vegetables like spinach and kale and iron supplementation.
Other health enhancing flavonoids can be found in dark chocolate, cocoa, raw cacao, soy beans, red wine, tea, blueberries, grapes, citrus fruits and pomegranates. The compounds in camomile tea are thought to act on the same parts of the brain as anti-anxiety drugs (1) and can be a good natural way to assist reduction of stress and anxiety in a dietary form - powerful stuff.
The anti-oxidant actions of flavonoids are activated by the changes made by our metabolism and it is interesting they also have a synergistic relationship with the transport, conversion and use of vitamin C in the body (2). This explains why so many foods which have high levels of vitamin C also have high levels of these beneficial compounds.
The health of our cardiovascular system has been shown in studies to be inversely related to our dietary intake of flavonoids (4), with trials demonstrating that the consumption of anthocyanidins and flavan-3-ols leads to improvements in endothelial vascular function and protects pancreatic beta cells from oxidative stress (6, 14). They also help to protect LDL cholesterol from oxidation and therefore lowers the risk of atherosclerosis. Rutin and hesperidin – flavonoids found in citrus fruits, have been shown to strengthen blood cells and can assist in the treatment of hemorrhoids and varicose veins (5). Several studies have even demonstrated that adding a spice and herb mix to beef when cooking (oregano, rosemary, garlic, ginger or turmeric, black pepper) can lead to a significant improvement in vascular and metabolic function several hours after the meal, demonstrating that the anti-oxidants from the mix provide protection from the pro-inflammatory action of the meat, the post-prandial (glucose) oxidative effect and lipid (fat) peroxidation. It has even been shown to inhibit the formation of malondialdehyde, a carcinogenic compound. Even a small glass of red wine consumed with a meat dish, or added when cooking has proven in studies to inhibit the formation of this compound (11,12,13). There are many reasons why the Mediterranean diet is so beneficial to our health - this is one possible example as to why. Clearly how we prepare our food is an important facet for our health long term. All the more reason to add plenty of herbs and spices to our hamburgers when prepping for a BBQ and not opting for the cheaper shop bought ones.
So how many servings should you be aiming for daily? A meta study carried out in 2017 and published in the International Journal of Epidemiology concluded that to provide protection against cancer we should be consuming 7 servings of fruit and vegetables a day. However, for cardiovascular disease, strokes and overall risk of mortality the intake proved to be higher at 10 servings a day. It is worth noting that fruits and vegetables contain a variety of nutrients (i.e. vitamin C, potassium and magnesium) and phytochemicals (including flavonoids and carotenoids). Other compounds i.e. glucosinolates in cruciferous vegetables induce detoxifying enzymes and intake of fruits, vegetables and fibre may help to balance and excrete hormone concentrations and assist hormone metabolism, all of which “are likely to act synergistically through several biological mechanisms to reduce risk of chronic diseases and premature mortality” and of course, they may also be helping by replacing less healthy foods in the diet (15). Lastly but not least, they also have a beneficial effect on gut microbiota through the ingestion of plant material (fibre) which plays a vital role in the inflammatory expression of the immune system and protection of the intestinal barrier function (16). A medium-size piece of fruit or a cup of lightly cooked vegetables counts as 2 servings. A meal-size salad alone may count as 4 servings or more.
Easy ways to add the protective effects of flavonoids into your day:
Place a few sprigs of rosemary into some drinking water
Place sprigs of rosemary, thyme or/and oregano into cold pressed oils and use for dressings
Add sprigs of herbs and a dash of turmeric and black pepper into a tray of vegetables and roast
Add a dash of cinnamon to your tea, juice, cereal or yoghurt
Add a teaspoon of turmeric and a dash of black pepper to scrambled eggs or an omelette
Make a ginger tea. Add slices of fresh ginger to stir frys
Place garlic into free range poultry, lamb or cook with roasted potatoes or mash and add to baked sweet potatoes
Add basil or coriander to salads or garnish on top stews, chilli’s or soups after serving
Add grapes, pomegranate seeds, chopped apple or slices of orange to salads
3) Yao LH, Jiang YM, Shi J, Tomás-Barberán FA, et al. Flavonoids in food and their health benefits.Plant Foods Hum Nutr. 2004;59(3):113-22. https://www.ncbi.nlm.nih.gov/pubmed/15678717
6) Wang X, Ouyang YY, Liu J, et al. Flavonoid intake and risk of CVD: a systematic review and meta-analysis of prospective cohort studies. Br J Nutr. 2014; 111(1):1-11. [Pubmed].
7) North Shore-Long Island Jewish Health System. ECGC In Green Tea Is Powerful Medicine Against Severe Sepsis, Lab Study Suggests. ScienceDaily. 2007; Nov.
8) Yeoh BS, Olvera RA, Singh V, Xiao X, et al. Epigallocatechin-3-Gallate Inhibition of Myeloperoxidase and Its Counter-Regulation by etary Iron and Lipocalin 2 in Murine Model of Gut Inflammation. The American Journal of Pathology, 2016; DOI: 10.1016/j.ajpath.2015.12.004
9) Fernandez JW, Rezai-Zadeh K, Obregon D, Tan J. EGCG functions through estrogen receptor-mediated activation of ADAM10 in the promotion of non-amyloidogenic processing of APP. Published online 2010; Sep
10) Yung-Hsi K, Richard A, Liao HS. Modulation of Endocrine Systems and Food Intake by Green Tea Epigallocatechin Gallate. Endocrinology, Volume 141, Issue 3, 1 2000; March, Pages 980–987. https://doi.org/10.1210/endo.141.3.7368
11) Zeka K, Ruparelia K, Randolph R, Budriesi R. at al. Flavonoids and Their Metabolites: Prevention in Cardiovascular Diseases and Diabetes. Diseases. 2017 Sep; 5(3): 19. Published online 2017 Sep 5. doi: 10.3390/diseases5030019. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5622335/
12) Zhang Y, Henning SM, Lee Ru-Po, Huang J, et al. Turmeric and black pepper spices decrease lipid peroxidation in meat patties during cooking. International Journal of Food Sciences and Nutrition.Volume 66, 2015. Issue 3. 2013; Nov. https://www.tandfonline.com/doi/full/10.3109/09637486.2014.1000837
13) Li Z, Henning SM, Zhang Y, Zerlin A, et al. Antioxidant-rich spice added to hamburger meat during cooking results in reduced meat, plasma, and urine malondialdehyde concentrations. Am J Clin Nutr. 2010 May; 91(5): 1180–1184. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2854897/
14) Zhang B, Kang M, Xie Q, Xu B, at al. Anthocyanins from Chinese bayberry extract protect β cells from oxidative stress-mediated injury via HO-1 upregulation. J. Agric. Food Chem. 2011;59:537–545. doi: 10.1021/jf1035405 [Pubmed]. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5622335/
15) Aune D, Giovannucci E, Boffetta P, Fadnes L, et al. Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality—a systematic review and dose-response meta-analysis of prospective studies. International Journal of Epidemiology, Volume 46, Issue 3, 1 June 2017, Pages 1029–1056. https://doi.org/10.1093/ije/dyw319
16) Minihane AM, Vinoy S, Russell WR, et al. Low-grade inflammation, diet composition and health: current research evidence and its translation. The British Journal of Nutrition. 2015;114(7):999-1012. doi:10.1017/S0007114515002093