This phenomenon is known as "assortative mating" - when men and women tend to select partners according to non-random attributes such as height, religion, age and smoking habits.
Researchers have suggested that assortative mating by obesity could increase the already high prevalence of obesity by helping to pass on genes promoting excess weight to the next generation.
To date, all studies investigating assortative mating for obesity have used body mass index or skin fold thickness to measure obesity, and many have not accounted for other potential contributing factors, Dr John R. Speakman of the Rowett Research Institute in Aberdeen, Scotland, and colleagues note.
Study done on couples
Rowett and his team used a technique called dual-energy X-ray absorptiometry (DXA) to get a more precise picture of levels of body fat in their study participants, which included 42 couples.
They used statistical techniques to measure and account for the effects of age, the postal code area where people had grown up, and the amount of time they had been in a relationship.
The researchers found that assortative mating for body composition had indeed occurred, with heavier people winding up with heavier mates.
It's not clear why this happens, Speakman and his team note; leaner individuals may choose one another first, they suggest, leaving overweight people a more limited mate pool to pick from.
Aside from the underlying reason, they add, the fact that people are becoming overweight and obese at earlier ages than ever before could be making assortative mating for obesity even more common, because it is "allowing singles in their late teens and early twenties to more easily distinguish partners with obese and lean phenotypes." - (Reuters Health)