The Five-a-day message is well known, but applying this does not seem to be filtering down into everyday life. Recent studies have shown that the average consumption of people in developed countries is three portions a day.
"These finding provide strong support for the recommendations encouraging the public to consume more than five servings of fruit and vegetables per day," wrote lead author Feng He from St George's University of London.
The meta-analysis study of eight prospective cohort studies (five from the US, three from Europe, and one from Japan) combined 257 551 individuals with an average follow-up time of 13 years.
After adjustment for confounding factors, the researchers quantitatively assessed the risk of stroke as a function of fruit and vegetable intake.
Individuals who ate between three to five portions per day had an 11 per cent lower risk of stroke than people who ate less than three portions per day. Eating five or more portions per day lowered the risk of stroke by 26 per cent.
The researchers could not determine the exact protective effect of a diet high in fruit and vegetables, but did highlight the presence of potassium, folate, fibre and antioxidants.
"Since raised blood pressure is the major cause of stroke, the blood pressure lowering effect of potassium could be one of the major mechanisms contributing to a reduced risk of stroke with an increased fruit and vegetable intake," said Feng He.
A 2002 study by the same authors (British Medical Journal Vol. 323, pp. 497-501) showed that potassium had a direct effect on strokes that appeared to be independent of its blood-pressure lowering effects, although the mechanism was not fully understood.
The scientists downplayed the role of folate, fibre and antioxidants: "the contribution of dietary folate, fibre, and antioxidants to a reduced risk of stroke in only speculative."
In an accompanying, independent comment, also in The Lancet (Vol. 367, pp. 278-279) Lyn Steffen from the University of Minnesota School of Public Health, said: "However, disease prevention might not be attributed to single-nutrients, but to the interaction of nutrient and non-nutrient components in whole foods."
Steffen called for public health strategies to be developed to push the Five-a-day diet.
"Partnerships must be formed between public health agencies, state and local government, schools, and the food industry and the media to promote healthy food choices," she said.
One limitation with this new study is the diet of the individuals themselves, since people who eat more than five portions of fruit and vegetables a day are probably less likely to smoke, have lower intakes of salt and fat, and be more physically active.
Another limitation that could have implications for the nutrients industry, and the food industry in general, was that the no distinction could be made as to "whether some types of fruit and vegetables were better than others."
A report from the European Union showed that global fruit and vegetable production was over 1 230 million tonnes in 2001-2002, worth over $50 billion (€41 000 million). Asia produced 61 per cent, with Europe and North/Central America both producing nine per cent.