Study co-authors Sarah Stewart-Brown, a professor of Public Health at Warwick Medical School in England, economist Andrew Oswald of the Department of Economics at the University of Warwick and David G. Blanchflower of Dartmouth College in New Hampshire studied the eating habits of 80,000 people in Britain.
The study, scheduled to be published in the journal Social Indicators Research, found mental well being appeared to rise with the number of daily portions of fruit and vegetables people consumed.
Well being peaked at seven portions a day, the researchers said.
Most western governments currently recommend to "strive for five" for cardiovascular health and as protection against cancer risk, Blanchflower said.
"The statistical power of fruit and vegetables was a surprise," Stewart-Brown said in a statement. "Diet has traditionally been ignored by well-being researchers."
One-quarter of Britain's population eat just one portion or no portions of fruit and vegetables per day, and one-tenth currently consume seven or more daily portions of fruit and vegetables.
The study does not distinguish among different kinds of fruits and vegetables. It defines a portion as approximately 3 ounces.