A poor night's sleep might leave you reaching for something sweet the following day. But what if your partner's restless night could affect your eating habits too?

New research suggests that sleep quality has consequences beyond the individual, potentially influencing both partners' food choices and their motivation to maintain a healthy diet.

The findings, published in Annals of Behavioral Medicine, offer a fresh perspective on the connection between sleep, relationships and everyday nutrition.

When Sleepless Nights Affect Two

Researchers led by Concordia University followed 204 couples living together in Canada over three months. The 408 participants had an average age of 42.4 years, and at least one person in each relationship had a body mass index of 25 or higher and was trying to improve their diet or physical activity.

Nearly 96% of participants reported actively working towards healthier eating habits.

Both partners completed questionnaires assessing sleep and diet quality at the beginning of the study, after one month and again after three months. They also kept daily diaries for the first 14 days, recording their efforts to maintain healthy eating routines.

This approach allowed researchers to examine how one person's sleep was associated with both their own dietary behaviour and that of their partner.

Why Your Partner's Sleep Matters

The findings revealed that poor sleep was associated with less healthy eating, even among people whose partners slept reasonably well.

Participants with poorer sleep reported making less effort to follow a healthy diet and feeling less confident in their ability to maintain good eating habits. Their partners experienced similar difficulties, independently of their own sleep quality.

Jean-Philippe Gouin, a psychology professor and corresponding author of the study, suggested that shared food environments could help explain this connection. A sleep-deprived person may be more inclined to choose tempting, calorie-dense snacks, potentially influencing what their partner eats.

However, this explanation remains a possibility rather than a mechanism directly established by the research.

Confidence Makes A Difference

The study identified two important factors connecting sleep and nutrition: self-efficacy and self-regulatory effort.

Self-efficacy refers to confidence in one's ability to achieve a goal, while self-regulatory effort describes the work involved in maintaining a desired behaviour.

When one partner slept poorly, the other tended to report lower confidence and reduced effort towards healthy eating. Statistical analysis suggested that these psychological factors partly explained the association between a partner's sleep quality and subsequent dietary habits.

Women generally reported healthier diets and greater efforts to maintain them than men. However, the researchers found no evidence that gender significantly changed how one partner's sleep related to the other's eating behaviour.

Why Shared Habits Deserve Attention

Across the three-month study, participants' diets improved modestly, while their sleep quality showed no significant overall change.

The researchers emphasised that the observational study cannot establish that insufficient sleep directly causes poorer eating habits. Sleep and dietary behaviour were also self-reported, introducing potential inaccuracies.

Future investigations could examine household food purchases, meal planning, relationship dynamics and objectively measured sleep.

Gouin suggested that lasting dietary improvements may require couples to consider their shared environment rather than focusing exclusively on individual willpower. The researchers also proposed investigating whether treatments for insomnia could benefit both partners' eating habits.

The findings highlight how closely everyday routines can become intertwined. Improving sleep may eventually prove useful not only for individual wellbeing but also for supporting healthier habits within a relationship.