The "five a day" rule should be doubled to 10 pieces of fruit and vegetables, a major study has said as it found that increasing consumption dramatically decreases the chance of disease.
Eating 800 grams of fruit and vegetables a day can reduce a person's chance of having a stroke by a third, while the risk of heart disease can drop by around 24 per cent.
It may also help stave off cardiovascular disease and cancer, while the study found that if everyone followed the new rule nearly 8 million premature deaths could be prevented worldwide.
Researchers from Imperial College London, who analysed data from 95 studies concerning fruit and vegetable intake, said they wanted to work out exactly what a person would need to eat to gain the maximum protection against disease.
But last night nutritionists warned that telling people to eat more portions could lead to add pressure and create "unrealistic expectations".
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 10 portions compared to people who ate none at all.
The research team also found that apples and pears, citrus fruits, salads and green leafy vegetables such as spinach, lettuce and chicory, and cruciferous vegetables, such as broccoli, cabbage and cauliflower, may help protect against heart disease, stroke, cardiovascular disease, and early death.
And cancer risk could be reduced by eating green vegetables, such as spinach or green beans, yellow vegetables, such as peppers and carrots, and cruciferous vegetables, they said.
Lead author Dr Dagfinn Aune, from the School of Public Health at Imperial, said: "We wanted to investigate how much fruit and vegetables you need to eat to gain the maximum protection against disease, and premature death.
"Our results suggest that although five portions of fruit and vegetables is good, 10 a day is even better. "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.
"It is clear from this work that a high intake of fruit and vegetables holds tremendous health benefits, and we should try to increase their intake in our diet."
Whilst consuming more than five portions of fruit and vegetables a day may be desirable, two thirds of adults currently don't consume the recommended minimum of 5-A-Day
Dr Alison Tedstone
The study, published in the International Journal of Epidemiology, also found that smaller intakes had benefits; a daily intake of two-and-a-half portions was associated with a 16 per cent reduced risk of heart disease, a 4 per cent lower risk of cancer and a 15 per cent reduction in the risk of premature death.
Meanwhile, a separate story published in the journal Thorax, found that a fruit and veg-rich diet is linked to much lower risk of chronic lung disease.
Experts assessed information on the health and dietary intakes of more than 44,000 men from Sweden. During a follow-up, almost 2,000 cases of chronic obstructive pulmonary disease (COPD) were diagnosed.
The authors found that those eating five or more daily servings were 35 per cent less likely to develop lung disease than those eating two or fewer daily servings.
Each additional serving was associated with a 4 per cent lower risk of COPD in former smokers and an 8 per cent lower risk in current smokers.
The British Thoracic Society stressed that people who smoke should know that kicking the habit is the most effective way of reducing their chances of developing COPD.
Dr Alison Tedstone, chief nutritionist at Public Health England, said: "The 5-A-Day target is the foundation of a healthy balanced diet and is an achievable way to help prevent a number of diseases.
"Whilst consuming more than five portions of fruit and vegetables a day may be desirable, two thirds of adults currently don't consume the recommended minimum of 5-A-Day.
"Adding pressure to consume more fruit and vegetables creates an unrealistic expectation."