Volumes of international studies demonstrate that a diet rich in fruits, vegetables, whole grains – the basics of the Mediterranean diet – are associated with lowered risk of various diseases and the promotion of mental health. While individualized diets might be tailored around this norm (e.g. whole grains may not be suitable for some), there is little doubt that a diet rich in minimally-processed plant foods is a coat of armor in a world where the risk of cardiovascular disease, obesity, diabetes, depression and other non-communicable diseases runs high. What is about whole plant foods that provide health resiliency?
First, minimally-processed plant foods are healthy because of what they don’t contain – added sugars, industrially-refined fats, synthetic emulsifiers, artificial sweeteners and the like. Whole plant foods are rich in nutrients – vitamins and minerals. One of the reasons why magnesium levels tend to be relatively low among North Americans is because we avoid its source – deep green leafy vegetables. Whole plant foods can also be a rich source of fibre which, of course, feeds our friendly gut bacteria and plays a critical role in gastrointestinal health. But whole plant foods are more than just healthy sources macronutrients, vitamins, minerals and fibre. They also contain phytonutrients, the natural chemicals that give plants their colour, taste and texture.
Scientists have identified about 25,000 phytochemicals found in global foods, but there are probably lots more. We know the most about the chemical class called polyphenols. In the North American diet these are consumed via tea, blueberries, grapes, apples, cherries, and green leafy vegetables. However, these are just a few examples – many are the deeply coloured fruits and vegetables which could (if only we would consume them!) provide polyphenols.
Interestingly, plants manufacture polyphenols when they are under threat from predators or disease. This is precisely the role played by polyphenols when consumed by humans – protection against pathogens. But much like fibre, scientists are now learning that polyphenols are acted upon by our friendly bacteria and may also play an important role in maintaining a healthy gastrointestinal tract.
And phytonutrients have recently been added to the new definition of prebiotics because they are capable of conferring health benefits when used by our gut microbes (meaning: they provide sustenance to the friendly gut microbes that live within us). After human consumption, sometimes polyphenols are absorbed unaltered, exactly as they are found in the plant. However, quite often the polyphenols are acted upon by our gut microbes and transformed into slightly different structures – metabolites – and these are better absorbed and delivered to various tissue sites where they work to protect cells and benefit the immune system.
Research shows that dietary polyphenols can have far-reaching effects in human health. Beyond fruit and vegetable intake per se, scientists have found that polyphenol intake is associated with lowered risk of many chronic diseases. This is exemplified in research linking total dietary phytonutrient intake and lowered risk of dying from all causes. But even more specifically, higher urinary levels of polyphenols (which provides a measure of those that have been consumed and absorbed) are linked to lower blood markers of inflammation and a decreased risk of dying.
As scientists continue to show the essentiality of polyphenols, it would seem logical to isolate some of the phytonutrients – let’s say the flavonoids or phenolic acids found in specific foods – and give them in pill form. But that hasn’t panned out too well. The available science shows that polyphenols work effectively as a collective. Indeed, there are plenty of studies which show the ability of phytonutrients to lower inflammation or protect cells against the damage of oxidative stress is far more effective when many are consumed vs. a single isolated polyphenol. While we have tons to learn about polyphenols, especially their seemingly intimate connection tom healthy gut microbes, scientists have known for more than two decades that the sum of health-protective properties of combined phytochemicals is far greater than that of their individual parts.
Alan C. Logan, ND is the co-author of The Secret Life of Your Microbiome: Why Nature and Biodiversity are Essential to Health and Happiness (New Society Publishers, 2017)
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