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New data from an Australian longitudinal study suggests romantic partnerships often coincide with modest but consistent weight gain. The pattern is surprising: married people tend to have healthier habits on paper, yet their average body mass index (BMI) climbs after entering a committed relationship.
What the study looked at and what it found
Researchers at the University of Queensland analyzed health records for more than 15,000 adults over a 10-year period (2005–2014). Reporting in PLoS One and covered by New Scientist, the team tracked BMI changes as participants transitioned into — or remained in — long-term relationships. Their headline finding: beginning a committed partnership often coincided with an increase in BMI, even though many couples adopted behaviors typically associated with better health.
Why do couples gain weight despite healthier habits?
At first glance the results seem contradictory. Married adults smoke less, drink less alcohol, and report higher fruit and vegetable consumption than single people. Yet they gain more weight. The lead researcher attributes this to psychological and social factors: comfort, lowered appearance-related pressures, and shared social meals.
Once a relationship stabilizes, the motivational incentives to stay thin for a potential partner diminish. That emotional ease can translate into more frequent indulgent meals, larger portion sizes, dessert ordering, and an overall relaxed attitude toward calorie-dense foods. Mealtime becomes social — and social meals are often more calorie-rich.
Additional drivers: kids, leftovers and lifestyle shifts
Parenthood amplifies the effect. Parents commonly sample children’s leftovers or snacks, increasing daily caloric intake. A complementary study from the University of Glasgow found newly married couples gained an average of 1.8–2.2 kilograms in the first year after marriage — a small but measurable shift in population weight trends.
Health trade-offs: less smoking, more calories
Being in a relationship is not uniformly bad for health. Married people often benefit from better mental health and lower rates of risky behaviors; divorced or single men, for example, are more likely to smoke or misuse alcohol than married men. In other words, romantic relationships appear to reduce some harmful habits while promoting others, such as overeating and reduced physical self-monitoring.
What this means for public health and individuals
For public-health researchers and clinicians, these findings highlight the need to address social and behavioral contexts around eating — not just individual choices. Couples-based interventions that encourage shared physical activity, mindful eating, and portion control could help mitigate relationship-related weight gain without undermining the social and emotional benefits of partnership.
Practical takeaways
- Watch portion sizes during social meals and date-night dinners.
- Make shared physical activities part of routine life together.
- Be mindful of the extra calories that come from kids’ snacks and leftovers.
- Focus on balanced, consistent habits rather than short-term dieting after weight gain occurs.
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