What's the science behind the emerging phytochemicals, polyphenols, and flavonoids trends?

When it comes to the new trend in polyphenols, flavanols and other phytochemicals, the first thing you should know is that these are not essential for nutrition. They are neither micronutrients (vitamins or minerals required in small amounts to aid the normal functions of a living thing) nor macronutrients (nutrients such as carbohydrates, fats and proteins which are required in large amounts for a living thing to survive). What they are instead are plant-based bioactive compounds that aid the functioning and health of an organism.

Every month new scientific discoveries are made into these amazing photochemical compounds based on cutting-edge research. Yet what is the evidence-based scientific research behind them and are they the next nutritional buzzwords ready for companies to sell stuff to you with?

What is a phytochemical?

A phytochemical (“Phyto” meaning plant) is a non-essential chemical produced by plants which help it attract pollinators and defend against bacteria, fungi, UV radiation and high temperatures. As new scientific discoveries are made every day, it has been found that there are many types of Phytochemicals, ranging from Carotenoids (beta-carotene in carrots for example) to Polyphenols (such as Flavanols), Phytosterols (such as phytoestrogen in Soya products), Terpenoids (substances which give plants and flowers their fragrance- think herbs and essential oils- such as lavender and cinnamon, citrus, eucalyptus, basil, pine, sage, mint, parsley, cannabis, rose, rosemary, peppercorn etc), Nitrogen-containing compounds (codeine, morphine, cocaine, quinine- also found in cocoa, tonic water, coffee and tea and peppers) and Organosulfur compounds (such as cruciferous vegetables like cabbage, Brussel sprouts, kale, watercress, rocket and broccoli). Many have been found to have health-boosting effects with huge medicinal potential.

Types of Phytochemical-Kings college London

What is a polyphenol?

By Dr Ana Rodriguez-Mateos, Professor King's college London.

A Polyphenol is a type of phytochemical found in many plants. There are many types Polyphenol, ranging from Stilbenes found in grapes to Flavenoids (Flavenols, Flavones, Flavanols, Flavanones, Anthocyanins and Isoflavones), Phenolic Acids (Hydroxycinnamic acid and Hydroxybenzoic acids) and Lignans, Curcuminoids and Ellagitannins. These chemicals usually occur bound to sugars such as the flavanols in red wine, tea, dark chocolate and apples. Fresh vegetables contain polyphenols in their skins and outer leaves (the parts most people usually throw away) and the riper a vegetable, the higher the flavonoid content. Fruit and vegetables grown in a field have more polyphenols than those grown in a greenhouse.

What does the evidence say about the health benefits of phytochemicals?

Phytochemicals have been found to have neutraceutical properties. A nutraceutical (also called a bioceutical) is defined as a pharmaceutical alternative which claims physiological biological benefits. Recent scientific trials (including a few prominent meta-analysis papers- the gold standard of scientific evidence)- have shown that phytochemicals, including polyphenols such as flavanols and flavenoids, have health benefits for the prevention and treatment of chronic diseases. These include.

• Cardiometabolic diseases- the study by Wang et al, found that flavonoids reduce CVD risk- 11% reduction from anthocyanidins, 10% reduction from proanthocyanins, 12% reduction from flavones, 12% from flavanones and 13% from flavan-3-ols (Wang et al., 2014). The study by Aune et al (Aune et al., 2018) also used biomarker analysis from blood analysis (which strengthens the reliability of the data), and found that total (n=1578) carotenoids reduce the risk of CVD, stroke, CHD and all-cause mortality (Aune et al., 2018) by 25% RR: 0.75 (0.64, 0.88 Cl). Additionally, carotenoids were found in the metanalysis study by Jiang, (Jiang et al., 2021), which found that increased beta-carotene reduced the risk of type two diabetes RR:0.78 (CI: 0.70, 0.87) with no significant impact from beta-cryptoxanthin and lycopene (highlighting that not every phytochemical has the same effect. Lycopene was found in a metanalysis by (Cheng et al., 2019) Cheng et al to reduce stroke risk by 26% RR: 0.74, (0.62–0.89, risk, CVD risk by 37% RR: 0.86, (0.77–0.95), and mortality risk by 14%, RR: 0.63, 0.49–0.81). This study also found that tomatoes and lycopene were associated with lower LDL-cholesterol and circulating proinflammatory Il-6.
• Age-related cognitive decline and neurodegenerative disease- Green tea flavanols are also associated with decreased cognitive decline (Ng et al., 2008) (Fusar-Poli et al., 2020)and curcumin has been found to have benefit for depression (Fusar-Poli et al., 2020) with n=10 studies, 531 participants, 25% risk reduction( 1.11 to -0.39), p < 0.001) and anxiety symptoms n=5 studies, 284 participants, p< 0.001). Polyphenols have also been found in metanalysis trials to improve BDGF (Ammar et al., 2020) and cognitive function(Cui et al., 2020).
• Cancer- The study by Aune et al also found that Carotenoids reduced cancer risk by 26%.
• Anti-Inflammatory action- Anthocyanins in berries have been shown to lower blood lipids (Yang et al., 2017) and improve vascular function (Fairlie-Jones et al., 2017).
• Modulation of the gut microbiome- Aune et al- found that polyphenols work in a bi-directional relationship with the gut microbiota, modulating the microbiota in a beneficial way (Aune et al, 2017).

This is a highly dynamic and interesting emerging field of nutritional science, and one with huge health-boosting potential. From cinnamon lowering blood sugar to plant sterols reducing circulating blood cholesterol, as Thomas Edison wrote in 1903, “the doctor of the future will no longer treat ill-health with drugs but rather will cure and prevent disease with nutrition.”

References

1. Ana Rodriguez-Mateos, Kings College London.
2. Aune, D., Giovannucci, E., Boffetta, P., Fadnes, L. T., Keum, N., Norat, T., Greenwood, D. C., Riboli, E., Vatten, L. J., & Tonstad, S. (2017). 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. Int J Epidemiol, 46(3), 1029–1056. https://doi.org/10.1093/ije/dyw319
3. Jiang, Y. W., Sun, Z. H., Tong, W. W., Yang, K., Guo, K. Q., Liu, G., & Pan, A. (2021). Dietary Intake and Circulating Concentrations of Carotenoids and Risk of Type 2 Diabetes: A Dose-Response Meta-Analysis of Prospective Observational Studies. Adv Nutr, 12(5), 1723–1733. https://doi.org/10.1093/advances/nmab048
4. Cheng, H. M., Koutsidis, G., Lodge, J. K., Ashor, A. W., Siervo, M., & Lara, J. (2019). Lycopene and tomato and risk of cardiovascular diseases: A systematic review and meta-analysis of epidemiological evidence. Crit Rev Food Sci Nutr, 59(1), 141–158. https://doi.org/10.1080/10408398.2017.1362630
5. Vauzour, D., Vafeiadou, K., Rodriguez-Mateos, A., Rendeiro, C. and Spencer, J.P., 2008. The neuroprotective potential of flavonoids: a multiplicity of effects. Genes & nutrition, 3(3), pp.115–126.
6. García-Conesa, M. T., Chambers, K., Combet, E., Pinto, P., Garcia-Aloy, M., Andrés-Lacueva, C., … & González-Sarrías, A. (2018). Meta-analysis of the effects of foods and derived products containing ellagitannins and anthocyanins on cardiometabolic biomarkers: Analysis of factors influencing variability of the individual responses. International journal of molecular sciences, 19(3), 694.
7. Craig, W. J. (1997). Phytochemicals: guardians of our health. Journal of the American Dietetic Association, 97(10), S199-S204.
8. Shaalan, E. A. S., Canyon, D., Younes, M. W. F., Abdel-Wahab, H., & Mansour, A. H. (2005). A review of botanical phytochemicals with mosquitocidal potential. Environment international, 31(8), 1149–1166.
9. Shaalan, E. A. S., Canyon, D., Younes, M. W. F., Abdel-Wahab, H., & Mansour, A. H. (2005). A review of botanical phytochemicals with mosquitocidal potential. Environment international, 31(8), 1149–1166.
10. Molyneux, R. J., Lee, S. T., Gardner, D. R., Panter, K. E., & James, L. F. (2007). Phytochemicals: the good, the bad and the ugly?. Phytochemistry, 68(22–24), 2973–2985.
11. Wang, X., Ouyang, Y. Y., Liu, J., & Zhao, G. (2014). Flavonoid intake and risk of CVD: a systematic review and meta-analysis of prospective cohort studies. Br J Nutr, 111(1), 1–11. https://doi.org/10.1017/s000711451300278x