When one person in a household has a rough night, the effects may spill over into more than just mood and energy.
A study of 204 couples living together in Canada found that poorer sleep in one partner was linked to less healthy eating in both people. The connection remained even after researchers took the other partner’s own sleep into account.
The study, published in the Annals of Behavioral Medicine, does not prove that one person’s poor sleep causes the other person to eat worse. But it highlights something that often gets overlooked: eating habits are shaped by the people we live with.
Researchers followed the couples for three months. Participants were 42 years old on average, and at least one person in each couple was overweight or obese and trying to improve their diet or physical activity. Nearly 96% said they were actively trying to eat better.
Both partners answered questions about their sleep and eating habits at the beginning of the study, after one month and after three months. For the first two weeks, they also kept daily diaries about how hard they were trying to eat well and how confident they felt about sticking with those goals.
At the start of the study, people who reported poorer sleep also tended to report less healthy eating habits.
Their partners did too.
In other words, one person’s sleep was linked not only to their own eating, but also to how the other person ate.
That may make sense when you think about how couples actually live. They often shop for groceries together, eat the same meals, share snacks and decide together whether to cook or order takeout.
A tired partner may be less interested in cooking or more likely to reach for easy, highly tempting foods. Once those foods are in the house or become part of the evening routine, they can influence both people.
“People with a sleep-deprived partner were essentially saying they have less confidence in their ability to follow a healthy diet, so they engage in less effort to do so,” study author Jean-Philippe Gouin said in a news release.
The daily diaries told a similar story. People whose partners slept poorly also tended to report putting in less effort to eat well and feeling less confident that they could stick with their goals. Those feelings were also linked with how well they ate later in the study.
But there is an important limit to what the study can tell us.
Poor sleep was linked with less healthy eating at the beginning of the study, but it did not predict how people’s eating habits changed over the next three months. In fact, participants’ eating habits improved slightly overall while sleep stayed about the same.
That means the study is better at showing that sleep and eating habits are connected within couples than proving that one partner’s poor sleep makes the other partner’s diet get worse over time.
Women in the study generally reported healthier eating habits and more effort toward their food goals than men. But researchers did not find evidence that the sleep-and-eating connection worked differently for men and women.
The results may not apply to every couple. Most participants were heterosexual, and all had lived together for at least a year. The study also specifically recruited couples in which at least one person was already trying to make a health-related change, so these participants may have been more focused on food and lifestyle than couples in general.
Sleep and eating habits were also based on what participants reported themselves rather than on sleep trackers or detailed food records.
Still, the study makes a relatable point: eating well can be a shared challenge.
If one person is exhausted, skips cooking, brings home snacks or suggests takeout, those choices can shape what both people eat. The same may be true in the other direction, where one partner’s healthier routines make it easier for the other to follow along.
“We need to consider the social contexts in which poor eating habits are taking place,” Gouin said. “That can involve asking how a partner is influencing one’s eating behavior, whether intentionally or not.”
Researchers say the next step is to test whether helping one partner sleep better can also help both people eat better.
For now, the findings suggest that healthy eating may be easier to maintain when couples think about their routines, food choices and sleep as things they share rather than completely separate habits.
“If we want to make changes that are long-lasting, both partners need to work together to change the home and food environment so that it is easier to maintain healthier habits over time,” Gouin said.
The study was funded by a Social Sciences and Humanities Research Council of Canada Insight Grant.