You've long known that eating more fruit and vegetables makes you healthier. But what if chomping on your greens made you happier too? 

Researchers at the University of Warwick and University of Queensland have made the startling discovery that eating more fruit and vegetables can substantially increase people's later happiness levels.

The study found that happiness levels kept increasing until participants consumed up to 8 portions of fruit and vegetables per day, Science Daily reported.

Results were dramatic. The difference in participants' happiness levels from eating no fruit and vegetables to having 8 portions a day was the equivalent of somebody going from being unemployed to having a job, researchers concluded. 

The study, which is to be published in the American Journal of Public Health,  followed more than 12,000 randomly selected people in Australia, with subjects keeping food diaries to track their eating habits and happiness levels. 

Professor Andrew Oswald said: "Eating fruit and vegetables apparently boosts our happiness far more quickly than it improves human health. People's motivation to eat healthy food is weakened by the fact that physical-health benefits, such as protecting against cancer, accrue decades later. However, well-being improvements from increased consumption of fruit and vegetables are closer to immediate."

Researchers say the findings might have implications for public policy, with eating healthily now having a psychological as well as physical pay-off.