Nov 15, 2016 3 min read

Dear Doctor K: You’ve mentioned phytonutrients in a few recent columns. What are they? And what can they do for our health?

Dear Reader: Let’s begin by breaking “phytonutrients” into its two parts. First, “nutrients.” These are chemicals in our environment that we need to get inside our body, usually through eating foods that contain them. Nutrients are a necessary part of our body chemistry. Indeed, many are necessary for the life of most living things.

Nutrients include carbohydrates, proteins and fats. They also include metals — such as iron, copper, iodine and zinc — and vitamins. I’d call oxygen and water nutrients, too.

Now to “phyto.” The word comes from the Greek word for “plant.” And that’s primarily where you can find phytonutrients — in plant foods such as fruits, vegetables, whole grains, dried beans and nuts. These natural compounds give plants their color, flavor, smell and texture.

Phytonutrients are powerful and healthy substances to include in your diet. There is growing evidence that they play a crucial role in helping to maintain human health and prevent a number of diseases, such as macular degeneration and some cancers.

There are as many as 2,000 known phytonutrients. Some of the better-known phytonutrients are isoflavones (in soy); lignans (in flaxseed and whole grains); carotenoids, such as beta-carotene (in carrots and dark, leafy greens); lutein and lycopene (in brightly colored fruits and vegetables); and flavonoids (in red-blue tinted fruits).

Choosing colorful foods (M&Ms don’t count) helps ensure that you get as many phytonutrients as possible. Typically, the deeper the color, the more phytonutrients present in the food. Notable exceptions are cauliflower, garlic and onions, and whole grains, which contain plenty of these healthful substances.

The growing interest in phytonutrients has created a vast supply of supplements lining store shelves. But in general, a pill can’t do what diet can. Getting your phytonutrients from plant-based foods ensures that you’ll get a variety of nutrients that work well together. A single serving of vegetables, for example, may provide more than 100 different phytonutrients. The crucial interaction of these phytonutrients is generally lost when you’re getting only one or two substances in a pill.

To maximize your intake of phytonutrients:

n Eat phytonutrient-rich foods frequently throughout the day. This helps keep blood levels of these components constant and ultimately more effective.

n Eat at least five to nine servings a day of fruits and vegetables.

n Create a meal around vegetables and fruits. Fill half your plate with color.

n Savor the skins of the fruits and vegetables you eat, assuming you like the taste. The skins often are rich in phytonutrients.

n Regularly include a wide array of whole grains in your diet.

n Cook your vegetables if that’s how you prefer to eat them. Most phytonutrients are heat-stable.

Dr. Komaroff is a physician and professor at Harvard Medical School.