Instead of nagging your spouse to lose weight, try going on a diet yourself

Tired of nagging your spouse to lose a few kilos? You might get better results by going on a diet yourself.

Health experts have seen that the weight status of couples tends to move in sync. It is often similar when they get married, and if one partner gains weight over time, the other does as well. In fact, researchers have found that if one half a couple becomes obese, the risk that the other will follow suit rises by 37 per cent.

There are signs that the reverse is true as well. A long-term population study in England suggests that when one spouse loses weight, a “ripple effect” extends to the other spouse. Another study of bariatric surgery patients found that nearly two-thirds of their spouses were lighter a year after the procedure, with a median weight loss of just under 1.5 kilos.

Researchers led by psychologist Amy Gorin of the University of Connecticut set out to see whether they could replicate these results in a randomised controlled trial. They recruited 130 couples in which one partner was willing to try a weight-loss programme and the other was not. To be included, the partner on the programme had to be either overweight or obese (with a body mass index between 27 and 40) and the other partner had to be overweight (with a BMI over 25).

Couples did not have to be married, though 121 of them were.

The couples were randomly assigned to one of two groups. In one group, one of the partners received a free six-month membership to Weight Watchers, which included access to meetings and the use of digital tools to track eating and exercise habits. (The study was funded in part by Weight Watchers International.) In the other group, one of the partners got a simple four-page handout with information about exercise and healthy eating.

All of the participants were weighed and measured by professionals at the start of the study, three months in, and at the six-month mark.

In both groups, the partners who actively participated in a weight-loss program generally succeeded in losing weight. After six months of effort, those in the Weight Watchers group lost 4.5 kilos (or 4.5 per cent of their body weight), on average, while those who got the handout lost nearly 3 kilos (or 3.2 per cent of their body weight), on average. Those differences were not large enough to be statistically significant.

But Gorin and her colleagues were more interested in what had happened to the other half of these couples.

The partners of those who used Weight Watchers lost nearly 2.25 kilos, on average, and the partners of those who got the worksheet lost a little more than 1.8 kilos, on average. After six months, the average percentage of weight loss was an identical 2.09 per cent for both groups.

For the people who weren’t actively trying to lose weight — but did so anyway — it didn’t matter whether their partner was using Weight Watchers or the “self-guided” approach detailed on the handout. Nor did it matter if they were male or female, or if they overweight or obese when their partners began their weight-loss programme.

Experts believe the health benefits of weight loss kick in after body mass drops by 3 per cent. Overall, 32 per cent of the nondieting partners achieved that goal.

The researchers created mathematical models to predict how much weight the study participants would lose in each three-month period. Those models had errors, but those errors followed a distinctive pattern.

“If one member of a couple lost more [or less] than predicted at any given time point, the other member of the couple also lost more [or less] than predicted,” the researchers wrote.

The results bolster the case that couples have a significant influence on each others’ weight — for good or for bad. But longer-term studies will be needed to see whether people can maintain this “ripple effect” weight loss, the team noted.

The researchers used direct mail and online advertisements to recruit study participants, and offered to pay them $100 each if they completed the study. They wound up with a sample that was 96 per cent Caucasian. Future studies will need to be more diverse to assess whether the ripple effect applies to other racial and ethnic groups, the researchers wrote.

Still, the findings should encourage health experts to find ways to “harness household and social dynamics to promote clinically significant weight loss”, Gorin and her colleagues concluded. Doing so “could improve the reach and cost-effectiveness of weight management programmes”.

The study appears in the March issue of the journal Obesity.