You've heard "eat your fruits and veggies." Here's the catch.

Eating fruits and vegetables is good for your heart. You knew that. Your grandmother knew that. The food pyramid knew that.

But new research adds a sneaky twist. It turns out that which fruits and vegetables you eat may matter just as much as how many. The secret lies in a group of natural plant compounds with a name that sounds like a tiny superhero team: flavanols.

What on earth are flavanols?

Flavanols belong to a larger family of plant chemicals called flavonoids. Flavonoids are the reason many fruits and vegetables come in such bold colors, and they help plants survive harsh sunlight, hungry pests, and disease. Basically, they are a plant's personal sunscreen and bodyguard rolled into one. When we eat foods loaded with flavonoids, some of that protective power can rub off on us too.

Flavanols are one specific branch of the flavonoid family tree. You'll find them in lots of fruits, vegetables, tea, and cocoa. (Yes, cocoa. Hold that thought, chocolate fans.) Once flavanols get inside your body, they appear to help your cardiovascular system, meaning your heart and blood vessels, in several impressive ways.

They help your blood vessels relax. The inner lining of your blood vessels is called the endothelium. Flavanols nudge the endothelium to produce a molecule called nitric oxide. Nitric oxide is like a "stand down" signal that tells blood vessels to relax and widen. Wider, more relaxed vessels mean lower blood pressure and smoother blood flow. (Side note: nitric oxide is the same molecule certain heart medicines try to boost. Your blackberries are quietly doing pharmaceutical level work.)

They calm inflammation. Long lasting, low grade inflammation slowly damages blood vessels and helps set the stage for heart disease. Flavanols have anti inflammatory effects that may help shield your vessels from that wear and tear.

They mop up cellular trash. Flavanols act as antioxidants, which means they neutralize unstable molecules called free radicals. Free radicals damage cells through a process called oxidative stress, and oxidative stress plays a role in heart disease. Picture free radicals as tiny troublemakers knocking things over, and antioxidants as the cleanup crew restoring order.

What the new research found (and why it raised eyebrows)

A team of scientists from the University of Reading, Harvard Medical School, the University of California Davis, and Mars, Inc. studied the diets of more than 30,000 people across the United Kingdom and the United States.

Here is the smart part. They did not just ask people what they ate, because let's be honest, humans are terrible at remembering and even worse at admitting how many cookies they had. Instead, the researchers measured biomarkers in people's bodies. Biomarkers are measurable substances (in this case, flavanol related compounds in blood and urine) that give an honest, objective picture of what someone actually ate and absorbed. No fibbing your way past a urine test.

The study, published in the journal Food & Function, turned up something surprising. Fewer than one in five people were getting enough flavanols to reach the level shown to lower heart disease risk. And get this: even people who faithfully ate the recommended five servings of fruits and vegetables a day still mostly fell short.

In other words, you can do everything right by the old rules and still miss the mark on flavanols.

How much do you actually need?

Earlier research points to a target. A large clinical trial called the COSMOS study (short for COcoa Supplement and Multivitamin Outcomes Study) found that getting 500 milligrams (mg) of flavanols per day significantly lowered the risk of dying from heart disease.

Why trust the COSMOS study so much? Because it was a randomized controlled trial, which is considered the gold standard of medical research. Here is what that means. Participants were randomly assigned to take either a flavanol supplement or a placebo (a harmless dummy pill with no active ingredient). On top of that, neither the participants nor the researchers knew who got which until the study ended. This setup, called double blinding, stops people's expectations from skewing the results. If nobody knows whether they got the real thing, nobody can accidentally fool themselves or the data.

The new research shows most people land well below that 500 mg goal, even when they follow standard healthy eating advice.

The flavanol all stars

Here are some of the best food sources of flavanols, ranked by how much they pack per serving. Print this and stick it on your fridge.

• Plums (about 500g, roughly 1 pound): about 450 mg

• Cranberries (about 250g, roughly 1 cup): about 300 mg

• Blackberries (about 200g, roughly 1.5 cups): about 250 mg

• Green tea (one 250 ml, roughly 8 oz cup): about 200 mg

• Broad beans / fava beans (80g, a small handful): about 140 mg

• Cherries (about 400g, roughly 2.5 cups): about 130 mg

• Apples with skin (one medium, about 200g): about 110 mg

• Strawberries (about 200g, roughly 1.5 cups): about 90 mg

• Blueberries (about 150g, roughly 1 cup): about 80 mg

• Pinto beans (40g, about 2 tablespoons dry): about 70 mg

Notice how wildly the numbers swing. A single cup of green tea delivers about 200 mg, while the same weight of some other foods barely registers. One quick note: peel that apple at your own risk, because much of the flavanol treasure hides in the skin. The skin is the best part nutritionally, which is the universe's way of rewarding people who are too lazy to peel.

Why "just eat more produce" isn't specific enough

These findings poke at an interesting question. Could dietary guidelines do more good if they told people which fruits and vegetables to focus on, instead of only how many?

One of the researchers, Professor Gunter Kuhnle of the University of Reading, put it nicely. The "five a day" message is right, he said, but we may need to think harder about which five. Different fruits and vegetables bring very different benefits beyond the basic vitamins and minerals. As scientists keep learning about compounds like flavanols, there's a real chance to make food advice sharper and more useful.

To be clear, this is not a reason to ditch your broccoli for blackberries and call it a day. Variety still wins, and every fruit and vegetable brings something to the table (sometimes literally). The point is that small, smart swaps can stack the deck a little more in your heart's favor.

The bottom line: Eating fruits and vegetables matters, full stop. But leaning into the flavanol heavy hitters, like blackberries, apples with the skin on, broad beans, plums, or a simple cup of green tea, could hand your heart a bit of extra armor. Sometimes the most powerful health upgrade isn't eating more. It's choosing better.

This article is for general education and isn't dietary advice tailored to any specific person. Flavanol-rich foods are part of a heart-healthy pattern, but they aren't medication and they don't replace blood pressure or cholesterol management when those numbers are off. If you take blood thinners like warfarin, talk to your prescriber before significantly increasing dark-chocolate or green-tea intake — vitamin K and other compounds can affect medication levels. The Mediterranean diet pattern as a whole has stronger evidence than any single food, so think "add flavanols" rather than "flavanols as a fix."