Add this to your laundry list of signs he might not be that into you. A new study claims that a partner’s sudden interest in weight loss could really mean they’re losing interest in you. German Professor Thomas Klein, who studies the link between happiness and body weight, found that people in steady relationships who abruptly begin to diet and exercise are possibly planning to break it up.

“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 told the Daily Mail.

So when one half of a couple suddenly shows interest in slimming down, Klein says, it’s often an indicator they’re “preparing for the partner market.’”

The researchers studied more than 2,000 people ages 16 to 55, and found that most single people weighed less than those in long-term relationships.

“People in a relationship feel less pressure and often put on weight as they do not watch their weight so much,” Klein says.

Dr. Abigail Hirsh, director of Power of Two online, says that while weight loss  could be a sign they’re preparing for the partner market, it could also be a sign they’re preparing for any number of markets.

“It might be the partner market. But it also might be the job market,” she says. “Or it might be ‘my kids are away at school, and I want to find myself again’ market.”

Relationship expert Leslie Seppinni of Los Angeles agrees, also noting that weight loss might be a sign of many things, but that an affair is a definite possibility.

“It could easily be a sign of cheating,” she says. “The person is no longer feeling bored and dissatisfied.  ”Instead, they are feeling alive and want to look their best.”

Ultimately, though, Seppinni believes  any major changes in a relationship should not go overlooked:

“Any time your partner makes a change in front of you, don’t sit back and let it go,” she says. “If out of the blue your partner is no longer a couch potato, you should want to know why.”