The study, by Imperial College London, calculated such eating habits could prevent 7.8 million premature deaths each year.
The team also identified specific fruit and veg that reduced the risk of cancer and heart disease.
The analysis showed even small amounts had a health boon, but more is even better.
A portion counts as 80g (3oz) of fruit or veg - the equivalent of a small banana, a pear or three heaped tablespoons of spinach or peas.
The conclusions were made by pooling data on 95 separate studies, involving two million people's eating habits.