Being in a happy and stable relationship is wonderful, but it could come at a great cost to your health and waistline, according to new research published in PLOS Genetics.

People tend to gain a few “love pounds” once they have entered a serious and comfortable relationship — with recent reports suggesting that 62 percent of couples gain around 14 lbs of “happy weight” after falling in love. It should come as no surprise that a new study found that the lifestyle people lead with their romantic partners has great impact on their risk of obesity.

Research out of the University of Edinburgh shows that middle-age couples' choices, especially in regard to diet and exercise, have a much greater influence on their chances of becoming obese than their upbring. This means the many nights couples spend staying in and watching televisions or eating out can overpower the instilled healthy habits each shared with their siblings and parents growing up, and conversely, a partner’s healthy habits could overturn the unhealthy ones instilled during childhood and adolescence.

“Although genetics accounts for a significant proportion of the variation between people, our study has shown that the environment you share with your partner in adulthood also influences whether you become obese and this is more important than your upbringing,” Chris Haley, who led the study, said in a statement. “The findings also show that even people who come from families with a history of obesity can reduce their risk by changing their lifestyle habits."

Researchers recruited up to 20,000 people from Scottish families and compared their family genetics and home environments in childhood and adulthood. They then related these to measures linked to health and obesity. Sixteen measures, including waist-to-hip ratio, blood pressure, body fat content, and body mass index, were considered. The findings suggested that common genetic variants, pedigree-associated genetic variants and recently-shared environment of couples are the most important contributors to variation in these traits, while past family and sibling environment have a limited impact.

The findings reinforce the message that it’s never too late to start healthy habits, as lifestyle changes in adulthood have a great impact in tackling obesity, regardless of genetic profile. Obesity, like many other medical conditions or disorders, is an interplay of genes, social environment, and behavior factors, which means actions and other environmental factors can influence how genes act within the body.

Source: Xia C, Amador C, Huffman J, et al. Pedigree- and SNP-Associated Genetics and Recent Environment are the Major Contributors to Anthropometric and Cardiometabolic Trait Variation. PLOS Genetics. 2016.