Consuming five portions of fruit or vegetables each day is linked to a lower risk of premature death but eating more portions appears to have no further effect, their study concluded.
The findings contradict recent research which found eating "seven a day" holds the lowest risk of death.
The latest study, published on thebmj.com, examined the association between fruit and vegetable intake and risk of premature deaths.
Researchers from China and the US analysed 16 studies involving more than 830,000 participants. Higher consumption of fruit and vegetables was associated with a lower risk of death from all causes, particularly cardiovascular disease.
They found the average risk of death from all causes was reduced by about 5% for each additional daily serving of fruit and vegetables.
But once five portions had been consumed, there was no additional benefit noted for extra portions.
The authors said: "This provides further evidence that a higher consumption of fruit and vegetables is associated with a lower risk of all-cause mortality, particularly cardiovascular mortality."
They added: "There was a threshold around five servings of fruit and vegetables a day, after which the risk of all cause mortality did not reduce further."