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Through Thick and Thin

Press Release No. 345/2011
3 November 2011
Heidelberg sociologists explain influence of partnership on body weight

People who are happy with their life partnership are more likely to put on weight than singles. One reason for this is competitive pressure on the partnership market. A study undertaken at Heidelberg University’s Max Weber Institute of Sociology proves the point. “When rivalry is fierce in connection with finding a partner,” says Prof. Dr. Thomas Klein, “singles will keep an eye on their weight in a bid to be more attractive. If there’s less competition, differences in weight between singles and people living in a partnership are less marked.” According to the Heidelberg sociologist, the weight similarities often found in couples are traceable not to adjustment processes during partnership but to a preference for people with a similar physique when selecting a partner.

Sociologically, the “negative protection” and “selection” mechanisms operative on the partnership market are well-established factors. Partnerships are often associated with weight increases. In other words, while steady relationships are demonstrably beneficial for health and life expectancy and are thus “protective”, a negative effect makes itself felt in the body weight sector. Equally well established is the fact that slimness improves the prospects of finding a partner (selection). Previously, however, the absence of data left it unclear what role the partnership market plays in the negative protection effect and to what extent weight similarity between partners is attributable to selection or adjustment.

To cast light on these issues, Prof. Klein and his team evaluated the data from the “Partnership Market Survey 2009”. This representative inquiry by the Heidelberg sociologists involved approximately 2,000 people between 16 and 55 and was the first to take account of conditions on the partnership market and the way they affect the motivation for weight-watching. It indicated that in a partnership “negative protection” is much less marked if singles have little to fear from rivals prior to partnership. “From this we can conclude that if there’s not too much competition on the partnership market, singles will pay less attention to their weight and accordingly not get much heavier in a partnership,” says Prof. Klein. “But if they anticipate strong rivalry, they will pay greater attention to their figure and get heavier as soon as a steady relationship stops them from having to worry about potential competitors.”

These findings are substantiated by the fact that the weight of people in partnerships that have run into trouble is frequently lower than in smooth-running relationships. “It is conceivable that this may also have to do with the fact that there are fewer joint meals or that the problems have psychosomatic repercussions,” Thomas Klein concedes. “But one can also interpret weight loss as a kind of preparation for a return to the partnership market, a concern for physical attractiveness caused by an awareness that it may soon be necessary to go in search of a partner again.”

Another conclusion to be drawn from the data is that the body mass index (BMI) of the responders is proportionate to that of the partner. But as the relationship wears on, there is no increase in weight similarity between the partners. “Accordingly, BMI similarity between partners rests on partner selection processes,” says Prof. Klein, “not on an adjustment of the partners to one another. Normally, slim people select slim partners and heavier people select heavier partners.”

Prof. Dr. Thomas Klein
Max Weber Institute of Sociology
phone: +49 6221 542972

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