Too much of a good thing: why choose food over supplements


You once had to be involved in science in some way to know the term polyphenol but in the past decade, these compounds have received more and more attention in nutrition circles. Polyphenols are a class of substances, found in plant foods (phytochemicals), that offer a wide range of disease-fighting properties.

Name a plant food that’s been linked to protection against an ailment and it’s likely there are polyphenols playing a role.  They offer an arsenal of weaponry against common chronic diseases including antioxidant action against cardiovascular disease, certain cancers, neurodegenerative diseases such as Alzheimer’s and more.  The names of various groups of polyphenols are numerous. Flavonoids, stilbenes  and lignans are just a few examples but consider that there are hundreds in the foods we eat. The polyphenols contribute to the stellar reputation of foods such as  extra virgin olive oil, dark chocolate, red wine,  apples, berries and tea. In fact, though, the list of polyphenol-rich selections includes whole grains, pulses, fruits, vegetables and nuts and seeds.

Yup –all plant foods.  These compounds are incredibly abundant in various healthy eating patterns such as the Mediterranean diet, the DASH diet and vegetarian eating patterns.

But as important as these compounds are to our health, in plants, they’re vital for their survival.  For example, the pigments which give plants their colour or substances responsible for  odours may attract insects that lead to pollination. And no pollination means no reproduction.  Other phytochemicals are actually part of the plant’s defense systems against various pests and  diseases or even too much sunlight. For example, the  bitter substances in citrus fruits  are an example of a defence mechanism.  In order to avoid being eaten, plants secrete a variety of toxins and  natural pesticides. But while some of these  very same substances, polyphenols for example, have been shown to act as disease-fighters in humans, in large doses, such as those found in supplements, however, these compounds may do to humans what small doses do to insects.

Overdoing phytochemicals when choosing a variety of foods has historically been a difficult task. Many of these substances, particularly the ones that are meant to deter pests from eating the plants, give foods a bitter taste. Excessive amounts of various phytochemicals in a food can make it virtually unpalatable. In fact, extreme bitterness in a food has almost been a natural safeguard for humans against poisoning.

But now it’s easy to overdo your polyphenol intake. Just peruse the supplement aisles or go online and check out the huge array of offerings.

The title of a recently published paper in the journal, Nutrients, Polyphenols, and DNA Damage: A Mixed Blessing captures the issue perfectly. The authors reviewed studies  published from 2010 to the present and included a total of 386 papers.

They conclude, “To summarise, results reported in the recent literature, on the whole, lend support to the hypothesis that dietary polyphenols protect the body against the effects of reactive oxygen species on DNA integrity, but do so reliably only when present at low concentrations.”  Large doses may go hand in hand with DNA damage (which can cause diseases such as cancer and accelerate ageing). As a result, the authors urge caution in the development of functional foods- options where various substances are added to foods to enhance their health benefits.

The past studies  showing the potentially  harmful effects of  high dose supplements have received too little attention. But it seems to be clear:  in the amounts you can consume in  whole foods, these compounds protect against disease but in larger amounts, such as those found in many supplements, they may cause DNA damage.

The message is clear: for health’s sake, get your polyphenols from real food.

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Categories: Nutrition News

Author:Rosie Schwartz

Rosie Schwartz is a Toronto-based consulting dietitian and writer.

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