There are many reasons we gain an extra few kilos on the scale – winter, pregnancy, good old-fashioned laziness. But is it your partner that’s making you carry around some excess weight?

Motherhood and menopause are two stages in a woman’s life that carry a higher risk of gaining weight. But research has nailed a third ‘M’ for women to be wary of: man. Moving in with your man can be a significant trigger for piling on the pounds.

University of Queensland researchers tracked the weight of 6458 Australian women over 10 years, finding that childless women in their late 20s and 30s who were married or living with their partner tend to put on more weight than single women. Add a baby to that equation and the weight goes up again – about 9.2 kilograms over a decade.

What’s surprising is that the childless-but-living-with-a-man group gained so much – an average of seven kilos – while single women without kids put on the least with 4.9 kilograms.

What we don’t know is why partnering is having an effect on women’s weight. Other research suggests that when couples live together, their eating habits often change to accommodate each other.

It could well be that we make more of an effort to impress with man-friendly meals, or change our eating patterns to fit in with his – including larger portions or integrating desserts or alcohol with your meals.

Earlier research has already shown that Australian women in their 20s and 30s are gaining kilos more rapidly than older women at mid-life. And while a few extra kilos at 28 or 35 might seem no big deal in the short term, it can mean trouble if you’re lugging them into that other weight-gain danger zone – 45 to 55 – when research says Australian women typically gain a further five kilos.

According to the study, motherhood typically piles on more than partnering up. But although women with one child and a partner put on more than nine kilograms over a 10-year period, the researchers say that it’s hard to untangle how much of this weight gain was influenced by partnering and how much by parenthood.