Soya isoflavones in particular have been shown to reduce cardiovascular disease risk as they inhibit the growth of cells that form artery-clogging plaque.
All of the 102 patients in the latest trial had suffered a first or recurrent ischaemic stroke -caused by a blood clot - in the previous six months and had established heart disease.
The patients were split into two groups, with one receiving a 12-week course of isoflavone as an 80mg daily dietary supplement, and the other given a dummy pill or placebo.
The scientists measured the way the brachial artery - the main artery of the arm - dilated in response to an increase in blood flow.
This measurement, the flow-mediated dilatation (FMD), is an indicator of the functioning of the cells that line the inner surfaces of blood vessels - the endothelium - which are implicated in cardiovascular disease.
At the start of the study the prevalence of impaired FMD was similar between the two groups.
But after 12 weeks, the FMD improved significantly in the patients given the isoflavone supplement.

The 50-year-old has cancelled several dates this year because of illness. The Royal Albert Hall gig itself had been rescheduled from May.
It seemed to be in jeopardy again when Morrissey was taken to hospital in Swindon on Saturday, after two members of his band carried him off stage.
A show in Bournemouth, due to take place on Monday, was postponed, but the star’s spokeswoman said he was now “rested and absolutely fine”.
Morrissey’s tour is due to move onto its European leg next month, including gigs in the Netherlands, France, Belgium, Germany and Ireland.
The former Smiths singer then tours the US throughout December.
Singer Morrissey returned to the stage at London’s Royal Albert Hall on Tuesday, and made light of his collapse during a recent concert in Swindon.
“Fasten your seatbelts it’s going to be a bumpy night,” he declared, launching into the Smiths’ hit This Charming Man.
That song had been the last one he played before collapsing with breathing difficulties on Saturday night.
In London, he pretended to faint again, before springing to his feet and declaring: “Thank you, Swindon!”
The taciturn star spoke briefly about his collapse, telling the sell-out crowd: “The doctor said I shouldn’t smile. I told him, ‘I don’t’.”

Poaching of the endangered one-horned rhino in Nepal is increasing due to inadequate security caused mainly by the Maoist insurgency, officials say.
The Nepalese authorities say that 31 rhinos have died in less than a year
This is said to be one of the highest number of rhino deaths in recent years and more than half the deaths have been blamed on poachers.
Nepal is home to more than 600 one-horned rhinos, accounting for a quarter of the total population which is mainly found in north-eastern India and Nepal.
The number of rhinos had been increasing in Nepal in recent years as a result of conservation schemes and security arrangements.
But recent reports of a high number of rhino deaths have alarmed the authorities.
The increase in poaching has been blamed largely on inadequate security caused by the long-running Maoist insurgency.
The government was forced to cut down the number of security posts established to counter the poachers after it deployed the military to tackle the rebels last year.
Trading in the horn of the rhino is internationally banned, but experts say that poachers are encouraged by the big profit margin.

For many years, Nepal has been widely regarded as a conservation success.
But now it is emerging as an international transit point for illegal wildlife goods, particularly those being moved between India and China.
Sandwiched between the two Asian giants, Nepal has devoted nearly 20% of its land to national parks and protected areas that have conserved endangered animal and plant species.
But outside such preserved areas, highways and mountain trails are increasingly becoming transit routes for wildlife traffickers, conservationists and officials say
The amount of wildlife goods seized in the recent past really tells us that Nepal is indeed a transit point,” says Prasanna Yonjan of Wildlife Conservation Nepal, an organisation that has helped authorities catch many traffickers and poachers.
“We know Nepal is a conduit for the international market, particularly the Orient. Most of the goods seized here are not products from Nepal but from down south, particularly India, Bangladesh and perhaps also from Bhutan.”
The superintendent of police, Devendra Subedi, who heads the crime branch in the capital, Kathmandu, says illegal wildlife trafficking has become a part of organised crime.
“There are several layers involved, and the people in it are found to be [involved] in other crimes like drug trafficking as well,” he explains.
So much so that even the country’s forest minister Matrika Prasad Yadav is well aware of the happenings. A former Maoist rebel leader, he even went on to say that several government agencies are involved in the trafficking network.
“One example is the smuggling of red sandalwood that comes in from India and is smuggled out to China,” he said in an interview for the BBC’s One Planet programme.
“I have documentary proof that even my own ministry, before I took over, allowed such smuggling by calling the red sandalwood ‘common wood’.
“Later when my ministry, and the finance and home ministries, opened checkpoints on highways, my staff were harrassed and threatened by the people of the other two ministries.
“When tonnes and tonnes of red sandalwood can be smuggled in and out, you can imagine what could be happening with things much smaller in size.”
But others point out that, as a former Maoist rebel, the minister has a track record of tough talk about other political parties.

Portugal winger Cristiano Ronaldo has been ruled out of his country’s 2010 World Cup play-off ties against Bosnia-Hercegovina on 14 and 18 November.
Ronaldo travelled to his homeland to have his ankle injury assessed, despite Spanish club Real Madrid claiming their player would not be fit enough to play.
“Cristiano was in Lisbon on Tuesday,” said Portugal’s football federation.
“The player is not in good enough physical condition to train with the squad ahead of the play-offs.”
The Portuguese FA said they wished Ronaldo a “good and rapid recovery” from an injury he picked up playing for Madrid in a Champions League game against Marseille on 30 September.
He has not played in seven games for the Spanish club since but did figure for Portugal in a World Cup qualifier against Hungary on 10 October when he aggravated the problem.
Portugal, World Cup semi-finalists in 2006, play Bosnia-Hercegovina in Lisbon and then Zenica four days later, with the aggregate winners qualifying for the 2010 finals in South Africa.

German referee Robert Hoyzer has admitted match-fixing charges and has promised to co-operate fully with an ongoing investigation.
“The accusations that have been raised in public are true,” he said. “I regret my behaviour profoundly and apologise.”
The German Football Federation had said he was under suspicion of rigging a Hamburg SV cup match last year.
The DFB investigation has now been widened to include five more matches Hoyzer was involved in.
He had initially denied the charges, but said on Thursday: “I have documented completely and unsparingly my behaviour and my entire substantial knowledge of all facts and people known to me in this matter.”
Hoyzer has told state prosecutors Friday that other referees and players were involved in the scandal, German newspaper Sueddeutsche Zeitung newspaper reported on Friday.
According to the newspaper, he said he had been present when other referees received money from a Croatian-controlled betting ring in Berlin and had heard of players getting paid.
Earlier in the week, Hoyzer’s lawyer strongly criticised the DFB’s handling of the case and said his client had been pressured into signing a resignation letter.
The match at the centre of the allegations involved Hamburg SV against lower-league Paderborn where Hoyzer sent off one Hamburg player and awarded Paderborn two penalties.
Hamburg were leading 2-0 but went on to lose 4-2. Manager Klaus Topmoeller was later sacked.

Real Madrid winger Cristiano Ronaldo is to consult his former specialist in the Netherlands after his ankle injury failed to show signs of improvement.
The £80m signing from Manchester United first sustained the problem to his right ankle in September and aggravated it playing for Portugal on 10 October.
He will now see Professor Niek van Dyjk who treated the same ankle in 2008.
“He cannot train and must continue treatment and relief work until another examination is made,” Real explained.
Early diagnosis of Ronaldo’s injury suggested he would be sidelined for between three and four weeks.
Instead the 24-year-old, who scored nine goals in helping Real win each of their opening seven competitive matches this season, has missed his team’s last seven games, only two of which have been won.

Uefa has drawn up legislation to prevent all players, management and referees from betting on games.
European football’s governing body has acted in the wake of the match-fixing scandal in Germany.
In January, referee Robert Hoyzer admitted to being involved in fixing a number of matches for financial gain.
Since then the German Football Federation (DFB) has confirmed it is investigating 25 people in connection with match-rigging.
DFB president Gerhard Mayer-Vorfelder said: “Uefa wants to introduce a code of honour so that players, coaches, management and referees in Europe cannot bet on matches.
“It is not just a German problem. Italy, Romania and the Czech Republic have also experienced problems with manipulation.”

Relations between the UK and the Kremlin reached a low after the murder in London of Russian emigre Alexander Litvinenko in November 2006.
But Mr Miliband insisted the UK’s continued demand for the extradition of the main suspect in the killing would not block co-operation on other issues.
The foreign secretary said the talks had been “substantive and productive” and marked by “mutual respect”.
He added that, although there were differences between the two countries, there had been a “genuine search for common ground and common action”.
Mr Miliband told reporters: “The cultural and business links that are growing, I think, are testimony to the importance of the UK-Russia relationship.
“That is reflected now at governmental level - not just on issues of the economy and foreign policy, but also on energy, climate change and other issues.”
He continued: “We don’t paper over our differences but we don’t allow them to block co-operation”.
Mr Miliband had met Sergei Lavrov for dinner and informal talks ahead of the meeting.
Discussions were expected to cover Iran, the Middle East and Afghanistan.
According to BBC diplomatic correspondent Bridget Kendall, a senior diplomat has indicated the main focus will be on issues where Russia’s collaboration is needed internationally - over Afghanistan, and over the question of Iran’s nuclear programme.
The aim, said the diplomat, was to be clearer about Russia’s position on Iran, and whether if current negotiations with Tehran failed, Russia would be prepared to adopt a tougher position.
The last British foreign secretary to visit Russia was Jack Straw in 2004. But Prime Minister Gordon Brown has spoken frequently with Russian president Dmitry Medvedev at international summits.
Ahead of his arrival, Mr Miliband said the UK still did not always “see eye to eye” with Russia but acknowledged it was a world power and an important trading partner.
Writing on his blog, Mr Miliband said: “We share the same global challenges and it is important that we work on them together.
“The wealth of people-to-people contacts and the dynamic business links which have grown between Britain and Russia over the last 20 years make political engagement all the more important.”
The Foreign Office said Mr Miliband would meet a range of politicians, business leaders and representatives of civil society before returning home on Tuesday.

Although the researchers cannot totally rule out the possibility that people with depression may eat a less healthy diet they believe it is unlikely to be the reason for the findings because there was no association with diet and previous diagnosis of depression.
Study author Dr Archana Singh-Manoux pointed out there is a chance the finding could be explained by a lifestyle factor they had not accounted for.
“There was a paper showing a Mediterranean diet was associated with a lower risk of depression but the problem with that is if you live in Britain the likelihood of you eating a Mediterranean diet is not very high.
“So we wanted to look at bit differently at the link between diet and mental health.”
It is not yet clear why some foods may protect against or increase the risk of depression but scientists think there may be a link with inflammation as with conditions such as heart disease.
Dr Andrew McCulloch, chief executive of the Mental Health Foundation, said: “This study adds to an existing body of solid research that shows the strong links between what we eat and our mental health.
“Major studies like this are crucial because they hold the key to us better understanding mental illness.”
He added people’s diets were becoming increasingly unhealthy.
“The UK population is consuming less nutritious, fresh produce and more saturated fats and sugars.
“We are particularly concerned about those who cannot access fresh produce easily or live in areas where there are a high number of fast food restaurants and takeaways.”
Margaret Edwards, head of strategy at the mental health charity SANE, said: “Physical and mental health are closely related, so we should not be too surprised by these results, but we hope there will be further research which may help us to understand more fully the relationship between diet and mental health.”