The Potential of Polyphenols

The old adage “we are what we eat” takes on new meaning as we learn more about the science behind how nutrition impacts both physical and mental health. There is a rapidly growing body of research that demonstrates the benefits of a largely plant-based diet. The Mediterranean diet has repeatedly been shown to be associated with healthy aging and increased resilience and resistance against chronic, non-communicable diseases (NCDs), including type 2 diabetes, early cognitive decline and heart disease. Both epidemiological and observational studies provide evidence that a Mediterranean diet featuring a large variety of vegetables, fruits, whole grains and healthy fats (like olive oil, nuts, avocado), is associated with reduced risk of cardiovascular, psychiatric, or neurologic disorders.

“…foods heavily emphasized in the Mediterranean diet.”

While fiber intake has long been at the focus of research into healthy diets, interest has turned to polyphenols (PPs) – a group of plant-based compounds, or “phytonutrients,” that naturally occur in many foods heavily emphasized in the Mediterranean diet. As secondary metabolites of plants, PPs help defend against stressors such as extreme temperatures, UV radiation, pests and diseases. A key mechanism in the production of these compounds by plants, is the communication between plant root systems and soil microbes. In preclinical studies these molecules serve similar roles as antioxidants that can neutralize damage from metabolic bi-products like reactive oxygen and nitrogen species. Even though this antioxidant mechanism may be important for some phytonutrients, surprisingly, it does not play a significant role after oral ingestion in humans.

“…the quantity and quality of PPs contained in foods is influenced by many factors such as climate, soil health, use of chemical fertilizers, stage of ripening, storage, processing and cooking.”

There are four main classes of PPs based on their chemical structures: phenolic acids, flavonoids, stilbenes and lignans. These can be further divided into subclasses, some of which have become familiar names for health-conscious consumers. For example, resveratrol is a stilbene polyphenol highly concentrated in red grapes and red wine. Quercetin is a flavonoid polyphenol found in almost all types of fruits and vegetables. Both are among the best studied PPs in preclinical studies with antioxidant, anti-microbial, anti-inflammatory properties. Some of these compounds have been evaluated for their potential use as nutraceuticals – dietary supplements to slow chronic disease development. Importantly, the quantity and quality of PPs contained in foods is influenced by many factors such as climate, soil health, use of chemical fertilizers, stage of ripening, storage, processing and cooking. However, several factors have raised early doubts about the benefit of these polyphenols, in particular the low levels of the parent compound detectable in the circulation after consumption and the enormous amount of red wine that one would have to consume to reach therapeutic levels, with the negative effect of the alcohol far outweighing the health benefits from the resveratrol.

“PPs are not just benefits for us, but also benefit our gut microbes and have been shown to alter the composition, function and metabolic activity of the gut microbiome.”

However, new research suggests that our gut microbiota may play a key role in how PPs exert health benefits in humans. Due to their large molecular size, about 90-95% of PPs are not absorbed in the small intestine and need to travel to the end of the small intestine and proximal colon, where they interact with gut microbes that break down the larger PP compounds into smaller, better absorbable ones. PPs are not just benefits for us, but also benefit our gut microbes and have been shown to alter the composition, function and metabolic activity of the gut microbiome. It is thought that these bi-directional influences facilitate positive change to our immune function, cardiovascular health and brain function by modulating inflammation, oxidative stress and communication between nerve cells.

Scientists are just beginning to unravel these complex relationships and there is much to still learn. Meanwhile, you may try enhancing your diet with PP rich foods like blueberries, cocoa, spinach, onion, olives, teas and spices (peppermint, oregano, celery seed, thyme, rosemary). However, as far as red wine is concerned, don’t consider the regular consumption of a glass of red wine as an important source of health promoting resveratrol of other flavonols. However, small amounts of red wine enjoyed with your dinner in the company of friends and family, are an important part of the Mediterranean lifestyle and contribute to your overall wellbeing.