Phytonutrients and your health: Beyond polyphenols

It’s beyond doubt that eating a plant-rich diet is good for you. Countless studies have shown that eating plenty of fruit, veg, nuts, and seeds is linked to better health and a longer life.

There are many reasons for this. Plants are a source of healthy carbohydrates, protein, and fiber to fuel your gut microbiome. They also contain a wide range of vitamins, minerals, and other micronutrients.

Another group of compounds called phytonutrients, or phytochemicals, also help provide some of plants’ incredible health powers. In this article, we’ll explain what they are, their health benefits, and where to find them.

What are phytonutrients?

Phytonutrients are defense chemicals produced by plants. They protect against infection by microbes, ultraviolet radiation from the sun, and the stress caused by hot or cold temperatures.

So far, scientists have discovered thousands of phytonutrients, and the list continues to grow. Although there are many more, today, we’ll cover four of the most well-studied categories:

• polyphenols

• carotenoids

• terpenoids

• phytosterols

There are plenty of unfamiliar chemical names below, but don’t worry about remembering them all. It just provides a sense of the wonderful complexity in every mouthful of plants you consume.

A final note before we get cracking: You don’t need to worry about increasing your intake of each individual phytochemical. If you focus on eating a diverse, plant-based diet, you’ll automatically consume a wide range of phytonutrients.

Powerful polyphenols

If you’ve followed ZOE for any length of time, you’ve probably heard us talk about polyphenols. These compounds occur in many plants, especially those that are brightly colored.

One example is anthocyanins, which produce the red, blue, and purple colors of many plants — the edible bits and the flowers.

Each of these subcategories contains a laundry list of other compounds. For instance, flavonoids are further broken down into flavanones, flavones, flavonols, and anthocyanidins. In all, scientists have identified more than 8,000 polyphenols.

Health benefits of polyphenols

Scientists have been interested in polyphenols for a long time, but there is still much to learn. So far, research suggests that polyphenols:

• Help mop up products of metabolism called free radicals, which can damage cells.

• Protect against cardiovascular disease; flavonoids seem particularly important here.

• Reduce the risk of some cancers.

• Protect against neurodegenerative conditions, such as Alzheimer’s disease — although not all researchers agree.

• Reduce inflammation.

Polyphenols are quite large compounds, so your gut only absorbs around 5–10% of them.

However, they feed “good” gut bacteria. And as our microbes ferment polyphenols, they produce a dizzying array of new, smaller compounds, which are easier to absorb and influence our health.

This is one reason why it is so challenging to understand the links between polyphenols (and other phytonutrients) and health: 

And this suite of metabolites probably varies depending on the types of bacteria in your gut — and everyone has a distinct microbiome, varying by sex, age, location, culture, and other factors.

There’s also the possibility that some gut bacteria feed on the myriad of polyphenol metabolites producing even more distinct compounds. Similarly, polyphenol metabolites that leave your gut and enter your blood then travel to your liver, where some are modified further.

It’s easy to imagine how polyphenols consumed by one person might have subtly different effects than in someone else. It’s also clear why getting to the bottom of phytonutrients’ health effects is tricky. 

Where to find polyphenols

Polyphenols are in most plants, but particularly colorful and bitter plants. But these foods have particularly high levels:

• cocoa powder (and good quality dark chocolate, as discussed in our excellent ZOE Science & Nutrition podcast episode with Spencer Hyman)

• artichoke

• blueberries

• blackcurrants

• spinach

• plum

• broccoli

• olive oil

• tea

• cherry

• strawberry 

• prunes

For a more comprehensive list, try this ZOE article on polyphenols.

Clever carotenoids

Carotenoids, as the name suggests, are found in carrots, but they also occur in many other orange, yellow, and red-colored plants. Scientists have now discovered well over 800 carotenoids.

Health benefits of carotenoids

As with polyphenols, carotenoids appear to have a range of health benefits, but once again, scientists are still ironing out the incredibly complicated details. However, these are some of their best-understood roles:

• Alpha-carotene, beta-carotene, and beta-cryptoxanthin are converted into vitamin A in your body.

• Lutein, lycopene, and fucoxanthin are powerful antioxidants.

• Lutein and zeaxanthin are found in the retina, and seem to play an important role in vision and eye health.

• Carotenoids appear to protect against some cancers.

Some experts also believe that fucoxanthin in brown algae might impart a range of beneficial effects. For instance, some research suggests it might help tackle obesity and reduce the risk of cancer, metabolic syndrome, heart disease, type 2 diabetes, and more. 

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Where to find carotenoids

The following are good sources of carotenoids:

• sweet potato

• carrot

• pumpkin

• tomatoes

• parsley

• orange

• daikon radish

• cabbage

• fenugreek

• purple turnip

• green leafy vegetables

Terrific terpenoids

Terpenoids, also called isoprenoids, are widely found in nature. Scientists have identified a staggering 80,000 types, making them the “most chemically and structurally diverse family of natural products.” They occur in virtually all natural foods. Impressive.

Health benefits of terpenoids

There has been relatively little research into the health benefits of terpenoids.

With tens of thousands of naturally occurring terpenoids, unpicking their precise role in health will take some time, but already there is evidence that they may support health.

However, it’s important to note that just because something works in a petri dish doesn’t necessarily mean it will work in a whole human.

Other terpenoids have been shown to extend the life of fruit flies, protect roundworms against oxidative stress, improve heart function in rats, and increase the growth rate of fish.

Where to find terpenoids

Terpenoids occur in almost all living organisms, and they often contribute to aromas and flavors, including those of:

• ginger

• eucalyptus

• lime

• orange

• grapefruit

• lemongrass

• saffron

• wine 

• frankincense and myrrh

Terpenoids have been used by humans throughout history. For instance, for thousands of years, people have carved ornaments out of amber — a fossilized plant sap terpenoid. 

A mixture of terpenoids creates pitch, which is used to water-proof homes and boats. And rubber, which is a natural terpene, has been widely used for all manner of things.

Fantastic phytosterols

Phytosterols is the collective term for plant stanols and sterols.

Phytosterols are an important structural component of membranes in plants, playing a similar role to cholesterol in humans and other animals. 

Health benefits of phytosterols

Experts have known since the 1950s that phytosterols can reduce levels of “bad” cholesterol. They seem to do this via a number of routes.

For instance, because phytosterols are similar to cholesterol, in your gut, they “compete” for absorption into your blood, meaning that less cholesterol can enter your circulation.

Because phytosterols can reduce blood cholesterol, manufacturers sometimes add them to spreads. The label might say that it includes “plant sterols” and proudly declare that the product will “reduce cholesterol levels.”

Scientists are still investigating this topic, which is made all the more challenging because people seem to respond differently to phytosterols.

Aside from lowering cholesterol, there’s some evidence that phytosterols may have antioxidant capabilities. Some studies even suggest that a phytosterol-rich diet can reduce cancer risk by 20%.

Phytosterols might also help combat obesity, high blood pressure, and inflammation, although the evidence isn’t conclusive.

Where to find phytosterols

Levels of phytosterols are high in:

• Nuts: Particularly pistachios and almonds.

• Wholegrains: Particularly flaxseed and wheat germ.

• Fruits and vegetables: Particularly corn, broccoli, and lettuce.

However, the richest sources of phytosterols are oils, including olive, sesame, sunflower, and peanut.

What does it all mean?

It’s undoubtable that a diet rich in plants will support good health. A significant chunk of these benefits may be thanks to phytonutrients.

The truth is, we’re only scratching the surface of phytonutrients. It’s highly likely that these compounds interact with each other and our gut bacteria, meaning that they have different effects in different people. 

So, while scientists continue to investigate the specific benefits of each of the thousands of compounds, try upping your plant intake.

Also, keep it varied — each plant has its own cocktail of plant chemicals, so focusing on variety will ensure you consume a wide range of phytonutrients. When it comes to plants, eating the rainbow really is a solid piece of advice.