Michelle RobertsDigital health editor
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Eating very specific types of fresh food each day - not just any five portions of fruit and vegetables - could help keep your heart healthy, a study suggests.
Not all five-a-days are equal, researchers claim, meaning people may not be getting enough important nutrients called flavanols in their diets.
Eating blueberries, plums, blackberries, broad beans and cherries, washed down with green tea, is an ideal way to top them up, they say.
In a study of 30,000 people from the US and UK - even in some who regularly ate five portions of fruit and veg a day - these were often lacking.
Other experts are more cautious, saying it is unclear if boosting flavanol levels would prevent heart problems.
According to new research in the journal Food and Function, fewer than one in five people get enough flavanols (500mg) into their bodies every day.
These antioxidants, found in certain foods, can support heart health, circulation and blood vessel elasticity by reducing inflammation, it says.
The study tracked people's diets and used biomarkers in the participants' urine to monitor intake.
Lead investigator Dr Javier Ottaviani said some simple food switches could "make a real difference" to how much of these beneficial compounds are absorbed.
"Most people assume that eating plenty of fruit and vegetables covers this, but what this research shows is that the specific choices you make matter far more than the total amount."
Investigator Prof Gunter Kuhnle, from the University of Reading, said while five-a-day was still the right message, we may need to think more carefully about which five.
"Different fruits and vegetables offer very different nutritional benefits beyond vitamins and minerals," he said.
"As our understanding of these compounds grows, there is a real opportunity to make dietary guidance more specific and more effective."
Foods with the higher flavanol content per portion, based on the researchers' tests, include:
- plums (one punnet) - 450mg
- cranberries (one punnet) - 300mg
- blackberries (punnet) - 250mg
- green tea (one 250ml cup) - 200mg
- broad beans (a small handful) - 140mg
- cherries (one punnet) - 130mg
- apple (one medium, skin on) -110mg
- strawberries (one punnet) - 90mg
- blueberries (one punnet) - 80mg
- pinto beans (two tablespoons) - 70mg
The researchers have been doing flavanol studies with the chocolate manufacturing giant Mars Inc, which is investigating cocoa flavanol supplements.
The British Heart Foundation (BHF) says the actual amount of flavanols in commercial chocolate - and indeed other foods - varies a lot.
Dark chocolate is often seen as a healthier choice than milk chocolate, because it contains less sugar and more cocoa, which is a source of flavanols.
Two or three squares of dark chocolate might contain between 22-73mg of flavanols, while a few chunks of milk chocolate will have 3-7mg.
Heart expert Prof Naveed Sattar, from the University of Glasgow, said although some small trials had shown some favourable effects of flavonoids on blood pressure, there was no real evidence yet showing actual reductions in heart disease outcomes.
He said more trials were needed before they could be recommended as a way "to reduce cardiovascular events", such as heart attacks and strokes.
Prof Ana Rodriguez-Mateos, an expert in nutrition at King's College London, said the levels of flavanol in fruit and vegetables can vary widely, as they also do in fibre content, and that this should be explored further.
Dell Stanford, from the BHF, says how much flavanol is contained in different products depends on where the food is grown, the climate, its ripeness, and how it is stored or processed - and also on who is eating it.
"Small amounts are absorbed directly. Our gut bacteria help break down flavanols into forms the body can use, but everyone's gut bacteria are different, so the benefits people get from flavanols may vary too."
The BHF and the British Nutrition Foundation say the best way to support your heart health is to follow established advice to eat a balanced diet containing a wide variety of fruit and vegetables.