We are told “eat your green vegetables”, but are they essential to our diet?

Shutterstock/Tijana Simic

Tim Spector

Author of Spoon-Fed: Why Almost Everything We’ve Been Told About Food Is Wrong, King’s College London, United Kingdom

We know that eating plants is good for us. In fact, the more the merrier. The ideal number for good health and our intestinal microbes is 30 different plants per week.

It’s not as hard as it looks, because that total includes nuts, seeds, fruits, legumes, beans, whole grains, and many other plants that aren’t green yet confer health benefits. But why eat vegetables first?

Plants get their color from a range of chemicals that help them thrive and survive. These polyphenols, such as red and blue anthocyanins, green chlorogenic acid, and yellow quercetin, are also the compounds we need to stay healthy.

There are hundreds of different polyphenols in cruciferous vegetables such as kale, broccoli, arugula, and cabbage. All of them have different beneficial impacts on our health thanks to their powerful effect on our gut microbiome. This community of microbes that live in our large intestine use polyphenols to make helpful chemicals known as postbiotics that affect everything from our immune response to our mental health.

Decades of evidence shows that increased consumption of green leafy vegetables is associated with better health outcomes: from reduced cancer risk to improved cognitive health, lower risk of type 2 diabetes and better pregnancy outcomes. It’s all thanks to the polyphenols and other nutrients found specifically in the colorful green leaves, plus another key ingredient that also feeds our gut microbes: fiber.

In addition to being high in fiber and polyphenols, green vegetables are low in a form of carbohydrate called starch. Unlike potatoes, carrots, corn, and beets, which contain enough starch to cause blood sugar to spike and impair our glucose metabolism and hunger, green vegetables do not have this effect and can therefore be consumed freely. Moreover, as I discuss in Spoon fedthere are leafy greens in season all year round.

Although the green parts of the plant have a high concentration of polyphenols, dark red or purple leaves can sometimes have even higher levels. But making sure we “eat our colorful greens” is the easiest way to remember to eat many different polyphenol-rich, non-starchy plants throughout the year.

John Brady

Sydney, New South Wales, Australia

Are the green parts of plants an integral part of our diet? The simple answer is no. Indeed, they can be dangerous for some people, due to the vitamin K1 concentrated in these foods. This vitamin helps with blood clotting and wound healing, but for those of us on the blood thinner warfarin, the vitamin K1 content of fresh green vegetables is an antidote to the drug.

I found this problem so frustrating that I recently published a cookbook for people on warfarin, explaining the options available to ensure safe eating habits.

All of the vitamins and minerals found in green vegetables are found in other foods, but with lower concentrations of vitamin K.

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