Overweight couples mating boosts obesity

People select partners of a similar size to them, according to scientists, who say the trend is contributing to Britain's obesity epidemic.

Scientists at the Rowett Research Institute, Aberdeen, and Aberdeen University found that people select mates with a similar amount of body fat to their own – passing on a "double dose" of genes that make someone susceptible to being obese.

Previous studies have shown that people "assortatively mate" – select partners with characteristics similar to our own – on the basis of age, height, social class, education and race.

Researchers have also shown a link between couples and their body mass indices – an indirect measure of body fatness.

But Dr Diane Jackson, of the Rowett Research Institute, said: "It has also been suspected that BMI may be linked to other things that people choose their partner by, such as social class or age.

"In our study, we corrected the results for all these other factors and we measured body fat using DXA (dual-energy X-ray absorptiometry), which is a much more accurate and reliable method of assessment than BMI.

"We also showed that the assortative mating for body fatness was not linked to the length of time that a couple had lived together."

The study – published in the August issue of the American Journal of Clinical Nutrition on Wednesday – involved 42 couples.

Professor John Speakman, of Aberdeen University, said it was not yet clear how overweight people end up together.

"Perhaps the social activities of the overweight and obese people coincide, making them more likely to meet partners who are also overweight and obese," he said.

Prof Speakman said assortative mating for body fat had increased over time, as people tend to choose partners and have children later in life.

"Nowadays, we choose partners and have children much later, but if we are going to become obese, on average we do so much younger," he said.

"This makes it possible for potential partners to select each other on the basis of body fatness."

The number of overweight people in the world overtook the number of malnourished for the first time in 2006, according to Professor Barry Popkin, director of the department of nutrition at the University of North Carolina.

Obesity costs the British economy as much as 7.4 billion pounds ($NZ9.8 billion) per year, and study published in the British Medical Journal warned in December that dealing with obesity could bankrupt the National Health Service.