London: If your partner has suddenly turned enlightened about health and started fighting flab, it's time to get cautious rather than feeling flattered -- for the change could be to please somebody other than you.

People who suddenly start fighting the flab while they're in an apparently steady relationship are secretly preparing to drop their other half, a daily reported a study as claiming.

According to sociologists, happy couples don't worry about their expanding waistlines because there is less pressure to look attractive.

"When you are on the lookout for a new partner people try to be as thin and attractive as possible,' Klein, of the University of Heidelberg, said.

Klein added: "People in a relationship feel less pressure and often put on weight as they do not watch their weight so much."

Researchers studied more than 2,000 people aged between 16 and 55. Among the findings was that people in couples generally weighed more than single people hoping to attract a partner in a competitive dating market.