Scientists at the Institute of Food Research have found that compounds present in the blood after eating a flavonoid rich meal reduce some early signs of heart disease
"We tested compounds that are actually found in the blood, rather than the flavonoid in food before it is eaten, as only these compounds will actually come into contact with human tissues and have an effect on arterial health", said research leader Paul Kroon.
There are six classes of flavonoids: flavonols, flavones, isoflavones, flavanones, flavan-3-ols and anthocyanins.
The scientists focused on the major flavonol in the diet, quercetin, the main sources of which are tea, onions, apples and red wine.
Previous IFR research has shown that quercetin is metabolised very quickly by the intestine and liver and is not actually found in human blood.
For this study, Kroon and his team analysed the compounds that enter the bloodstream after quercetin is ingested, absorbed and metabolised and used them to treat cells in a simple model of atherosclerosis.
"The effect is more subtle than laboratory experiments using the parent compound.
"But we can confirm that eating quercetin-rich foods may help prevent chronic inflammation leading to cardiovascular disease because the metabolites still have an effect on the cells lining the blood vessels", said Kroon.
The biological activity of flavonoids is highly dependent on their structure, and quercetin metabolites have very different activities from those of the parent compound.
"In order to assess the contribution of diets rich in fruit and vegetables to protect against cardiovascular disease, it is crucial that laboratory studies use the relevant compounds and most importantly, at concentrations achievable through diet".
This is one of very few studies that have used concentrations of quercetin metabolites that are achievable after eating quercetin rich foods, such as onions.
It was the first study to investigate all the major metabolites.
It was possible because the scientists synthesised the exact compounds found in the blood after eating a quercetin rich meal.
In the case of one inflammatory process, a lower dose actually had a larger impact.
This indicates that if something is good for you, it does not necessarily follow that more is even better for you.
Also, the lower dose was achievable through diet, for example by consuming 100-200g of onions.
People with high intakes of fruit and vegetables have been found to have a lower risk of cardiovascular disease and it was originally thought this was due to the antioxidant nutrients in plant material.
However, research failed to observe beneficial effects in terms of preventing CVD and recently interest has focused on the protective role that flavonoids may have.
Flavonoids are polyphenolic compounds naturally present in fruit and vegetables.
The research, to be published in Atherosclerosis, was funded through a Biotechnology and Biological Sciences Research Council (BBSRC) responsive mode grant to IFR.
