While five portions of fruit and veg a day is good for you, eating 10 is dramatically better, researchers have found.
They say a fruit and vegetable intake above five-a-day shows major benefit in reducing the chance of heart attack, stroke, cancer and early death, and could prevent up to 7.8 million premature deaths worldwide every year.
The new research, led by scientists from Imperial College London, analysed 95 studies on fruit and vegetable intake.
The team found that although even the recommended five portions of fruit and vegetables a day reduced disease risk, the greatest benefit came from eating 800g a day, which is roughly equivalent to ten portions.
'Our results suggest that although five portions of fruit and vegetables is good, ten a day is even better', said Dr Dagfinn Aune, lead author of the research from the School of Public Health at Imperial.
The study, which was a meta-analysis of all available research in populations worldwide, included up to 2 million people, and assessed up to 43,000 cases of heart disease, 47,000 cases of stroke, 81,000 cases of cardiovascular disease, 112,000 cancer cases and 94,000 deaths.
In the research, which is published in the International Journal of Epidemiology, the team estimate approximately 7.8 million premature deaths worldwide could be potentially prevented every year if people ate 10 portions, or 800 g, of fruit and vegetables a day.
This risk was calculated in comparison to not eating any fruit and vegetables.
Dr Aune said that several potential mechanisms could explain why fruit and vegetables have such profound health benefits.
'Fruit and vegetables have been shown to reduce cholesterol levels, blood pressure, and to boost the health of our blood vessels and immune system.
This may be due to the complex network of nutrients they hold.
'For instance they contain many antioxidants, which may reduce DNA damage, and lead to a reduction in cancer risk,' he said.
Dr Aune added that compounds called glucosinolates in cruciferous vegetables, such as broccoli, activate enzymes that may help prevent cancer.
Furthermore fruit and vegetables may also have a beneficial effect on the naturally-occurring bacteria in our gut.
The vast array of beneficial compounds cannot be easily replicated in a pill, he said: 'Most likely it is the whole package of beneficial nutrients you obtain by eating fruits and vegetables that is crucial is health.
'This is why it is important to eat whole plant foods to get the benefit, instead of taking antioxidant or vitamin supplements; which have not been shown to reduce disease risk.'
In the analysis, the team took into account other factors, such as a person's weight, smoking, physical activity levels, and overall diet, but still found that fruit and vegetables were beneficial.
'We need further research into the effects of specific types of fruits and vegetables and preparation methods of fruit and vegetables,' said Dr Aune.
'We also need more research on the relationship between fruit and vegetable intake with causes of death other than cancer and cardiovascular disease.
'However, it is clear from this work that a high intake of fruit and vegetables hold tremendous health benefits, and we should try to increase their intake in our diet.'