But a third of participants in the study said busy lifestyles meant they couldn't prepare healthy meals.

"These people were more likely to have smaller intakes of fruit and vegetables over the 20 years than those who did not say a lack of time had influenced their diet.

"However, it was perceived lack of time, rather than actual free time, that influenced people's food choices," the researchers said.

There was also a divergence between the sexes when it came to the ability of partners to sway eating habits.

A third of people, mainly men, said their partners had a positive influence on their diet while about 10 percent of participants, mainly women, said the effect was negative.

"We also need to examine the availability of healthy food in venues such as the workplace and in shops. Despite all the healthy eating messages, it's still easier to go to a local shop and buy a chocolate bar rather than a piece of fruit," said the study's lead author, dietician Amelia Lake.

The research was funded by the Wellcome Trust and published in the academic journal Appetite.