Polyphenols are a group of plant compounds which have a number of health benefits.
We often discuss polyphenols in nutrition, especially on this web-site. There is a lot of research which covers the role of polyphenols in nutrition. If you regularly consume foods containing plenty of polyphenols then there are strong associations with alleviating the issues of chronic diseases. Chronic diseases include the likes of stroke, cardiovascular diseases, metabolic syndrome, type 2 diabetes, and particular types of cancer. They also have an impact in improving general digestion and overall health.
So many foods contain polyphenols. They are all plant based so consuming vegetables and fruits should deliver a high level of these polyphenols. They are also obtained from processed and fermented foods too. Consider red wine, chocolate, berries, tea and coffee which are all good sources. These compounds are also found in a variety of other plants.
The amount and type of polyphenols in our food depends on growing conditions, the cultivar, growing conditions and how they are treated after harvesting. Cooking and preparation are two major processes which influence the quality of the polyphenols we consume. In some cases they may even improve the quality.
Type of Polyphenols
Over 8,300 types of polyphenols have been identified and there are still many which remain undiscovered or uncharacterised. They all have a typical phenolic structure.
Polyphenols can be further categorized into 4 main groups:-
- Flavonoids. These account for around 60% of all polyphenols and are the largest group of phenolic compounds. Examples on our web-site include quercetin, kaempferol, catechins, and anthocyanins. These are found in foods like apples, onions, dark chocolate, and red cabbage.
- Phenolic acids. This group accounts for around 30% of all polyphenols. Examples include stilbenes and lignans, which are mostly found in fruits, vegetables, whole grains, and seeds.
- Polyphenolic amides. This group includes the capsaicinoids found in chili peppers and the avenanthramides in oats.
- Other polyphenols. This general, all-embracing group includes everything else. Take for example resveratrol in red wine which is a stilbene, ellagic acid in berries, curcumin in turmeric, and the lignans in flax seeds, sesame seeds, and whole grains.
The amount and type of polyphenols in foods depend on the source, including its origin, ripeness, and how it was farmed, transported, stored, and prepared. A diet rich in polyphenols might be the Mediterranean diet. This is a diet rich in polyphenol-containing foods such as red wine, olive oil, fruits and vegetables etc.
Polyphenol-containing supplements are available as well. However, they’re likely to be less beneficial than polyphenol-rich foods although this has still to be established. The protective effects of polyphenols in the body also depends on their extraction from food, the level of intestinal absorption, their metabolism, and biological action with target tissues. Everybody is different, the intake of dietary polyphenols which are found in the plasma and the urine are different from one person to the next. One of the main reasons for such differences is probably due to the different gut microbiota composition and a host of genetic polymorphisms (essentially our genetic make-up), and this in particular is often difficult to link to unambiguous health effects.
The reasons why polyphenols work has been attributed to their anti-inflammatory properties and their antioxiodant properties in many cases. It is also thought that many of their benefits are due to interactions with signaling proteins (Kostyuk et al., 2011).
Polyphenols And a Reduction In Death From All Causes.
The Mediterranean Diet is a diet rich in polyphenols. A large primary prevention study examined the long-term benefits of this diet on the occurrence of cardiovascular disease (CVD) in particular but also overall death (all cause mortality). The people studied were at high risk but who did not at the time have CVD. It was known as the PREDIMED study.
The PREDIMED study was based on collecting food consumption data through diaries and a managed food frequency questionnaire. The polyphenol content of all the food consumed was estimated from the Phenol-Explorer database.
Amongst the high-risk participants, anybody with a higher polyphenol intake demonstrated a 37% lower mortality risk compared with those groups with a lower intake. Examining the types of polyphenols consumed, the stilbenes and lignans showed the highest benefit. The flavonoids and phenolic acids had no significant effect on reducing death.
Polyphenols And Heart Disease
Some general clinical studies show that polyphenols could reduce the risk of heart disease including atherosclerosis by positively reducing various risk factors associated with the condition.
The PREDIMED study we described earlier showed that there was a significant reduction in a variety of heart disease related events. Death from heart disease was also reduced. This was linked to a higher intake of polyphenols of a general nature (Tresserra-Rimabu et al., 2014b).
Consumption of cocoa polyphenols which are mainly flavonoids were found to produce a significant decrease in blood pressure if they were consumed daily for a fortnight (Shrime et al., 2011).
Cocoa generally significantly decreases the levels of LDL (bad) cholesterol and raises the levels of HDL (good) cholesterol in the body. The affect is attributed to the presence of cocoa polyphenols.
Diabetes
Kim et al., (2016) conducted a very thorough review of the benefits of consuming polyphenols and reducing the risk of type-2 diabetes. They summarized all the epidemiological and clinical studies up to that time. There is not a lot of evidence even now regarding studies on humans although there is plenty of information from animal and cell studies. Generally, consuming plenty of polyphenols is associated with a lower risk of type-2 diabetes but as they state, it is not always obvious.
The mechanisms by which polyphenols might exert their benefit is through protecting the β-cells that produce insulin in the pancreas from glucose toxicity. They can also stimulate insulin secretion. They may also inhibit salivary and pancreatic α-amylase and α-glucosidase which are involved in carbohydrate metabolism to produce glucose.
Weight Management
The Mediterranean Diet has long been cited as a diet for those wishing to reduce weight and manage it too. One of the main components is olive oil which has one of the highest concentrations of polyphenols of all the food we might encounter. There is very strong evidence that consuming olive oil in appropriate amounts helps not only with preventing cardiovascular disease and strokes but also mitigating the effects of metabolic syndrome and reducing some cancers.
Not all olive oils are the same but extra virgin olive oil is regarded as the best because of it contains relatively healthy fats. If part of a diet, there is research which suggests that this oil compared to others is very effective in maintaining a health lifestyle and in helping us mane our weight.
Polyphenols And Neurodegenerative Diseases
References
Hanhineva, K.; Törrönen, R.; Bondia-Pons, I.; Pekkinen, J.; Kolehmainen, M.; Mykkänen, H.; Poutanen, K. (2010) Impact of Dietary Polyphenols on Carbohydrate Metabolism. Int J Mol Sci. 2010, 11, pp. 1365–1402
Kim, Y., Keogh, J.B., Clifton, P.M. (2016) Polyphenols and Glycemic Control. Nutrients. 2016;8(1):17. Published 2016 Jan 5. doi:10.3390/nu8010017
Kostyuk, V.A.; Potapovich, A.I.; Suhan, T.O.; de Luca, C.; Korkina, L.G. (2011) Antioxidant and signal modulation properties of plant polyphenols in controlling vascular inflammation. Eur. J. Pharmacol. 658, pp. 248–256
Shrime, M. G., Bauer, S. R., McDonald, A. C., Chowdhury, N. H., Coltart, C. E., & Ding, E. L. (2011). Flavonoid-rich cocoa consumption affects multiple cardiovascular risk factors in a meta-analysis of short-term studies. Journal of Nutrition, 141(11), pp. 1982-1988 (Article)
Tresserra-Rimbau, A., Rimm, E. B., Medina-Remón, A., Martínez-González, M. A., López-Sabater, M. C., Covas, M. I., … & Arós, F. (2014). Polyphenol intake and mortality risk: a re-analysis of the PREDIMED trial. BMC Medicine, 12(1), 77 (Article).
Tresserra-Rimbau, A., Rimm, E. B., Medina-Remón, A., Martínez-González, M. A., De la Torre, R., Corella, D., … & Fiol, M. (2014b). Inverse association between habitual polyphenol intake and incidence of cardiovascular events in the PREDIMED study. Nutrition, Metabolism and Cardiovascular Diseases, 24(6), pp. 639-647 (Article).
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