Single marriages are associated with weight gain and problems with brain and intestinal function

To reach this conclusion, researchers at the University of California, Los Angeles, in the US, examined 94 adults from Los Angeles using brain imaging, analysis of intestinal metabolites, and blood tests to measure oxytocin. The findings reveal that marriage without romantic attachment may not provide the health benefits often associated with marriage, at least when it comes to weight.

Participants completed a brief questionnaire about whether they received emotional support and comfort from others. The researchers then divided the married and single groups based on their reported levels of emotional support (high or low).

The results were great for married couples. Those who reported low emotional support had a significantly higher BMI than their married peers who received good support. This pattern was not replicated among individual participants, whose levels of emotional support were not related to weight.

The researchers also assessed symptoms of binge eating using a validated scale. Participants who felt less emotional support reported more of these behaviors, including feeling unable to stop eating certain foods despite warnings.

When participants viewed images of food while lying down in an MRI scanner, their brain activity differed depending on the quality of the relationship. Married individuals with high emotional support showed stronger responses in the dorsolateral prefrontal cortex, an area involved in self-control and resistance to impulses.

Married participants who did not receive this support did not show the same pattern. Their brain responses to the food images were similar to those of single individuals, regardless of the level of support.

The dorsolateral prefrontal cortex helps people pause before acting impulsively, weigh long-term consequences against immediate gratification, and regulate desires. Imbalances in this area have been linked to obesity, depression, anxiety, and chronic pain in other research. The present finding suggests that marriages without mutual support may be associated with an impaired response in this region when faced with food stimuli.

Researchers speculate that healthy marriages function as an ongoing practice of self-control. Partners need to regularly put aside selfish motives, consider each other’s needs, and work toward common goals. This frequent exercise can strengthen the neural circuits involved in regulating motivation, with benefits extending to eating behavior.

Romantic marriages may not provide this training effect. Without the motivation to suppress immediate desires for the benefit of a partner, these self-control circuits may remain underpracticed.

Gut chemistry vs. relationship quality

The study also analyzed stool samples to examine tryptophan metabolites, which are compounds produced when gut bacteria break down this essential amino acid. Tryptophan serves as a raw material for serotonin and other molecules involved in mood, appetite, and immune function.

Participants with less emotional support presented different metabolic profiles. They showed reduced levels of indole and indole-3-carboxylate, compounds associated with anti-inflammatory and anti-neuroprotective effects. They also had elevated levels of indoxyl-3 sulfate, a uremic toxin linked to oxidative stress, inflammation, and cognitive decline.

Among married participants specifically, those with low support had lower levels of picolinate, a tryptophan derivative that has immune regulatory properties. Low levels of picolinate have been observed in people suffering from depression and neurological diseases.

The gut findings support the brain findings, suggesting that unsupportive relationships may be related to biological systems that regulate appetite and metabolism operating in a less favorable state.

Oxytocin could be to blame

Married participants tended to have higher blood levels of oxytocin than unmarried participants, although this difference was statistically marginal. Often called the bonding hormone, oxytocin is released during physical affection, emotional intimacy, and moments of connection. Studies have also shown that it reduces food intake and mitigates reward-based eating.

The researchers used statistical modeling to test whether oxytocin could link relationship quality to differences in the brain and gut. Their analysis confirmed the pathway by which positive relationships increase oxytocin, which in turn regulates prefrontal activity in the brain and intestinal tryptophan metabolism.

If marriages without emotional support fail to stimulate sufficient oxytocin release, subsequent effects on brain function and gut chemistry may help explain the higher BMI in this group, although more research is needed to confirm this pathway.

Oxytocin administration has been studied as a potential treatment for obesity, with some clinical trials showing decreased calorie intake and increased activity in areas of the brain associated with self-control. The UCLA findings suggest that relationship quality can naturally influence this same system.

It is important to note that the study has limitations. For example, a single moment was captured, rather than following participants over months or years. It is not possible to determine, from this design, whether marriage without emotional support causes weight gain or whether there are other factors that explain relationship quality and BMI.

The sample included 94 Hispanic adults from the Los Angeles area. The majority had a BMI in the overweight or obese range. Married participants were, on average, older than unmarried participants. Although the researchers controlled for age statistically, unmeasured differences between the two groups may have influenced the results.

The emotional support scale consists of only two questions, and the researchers divided participants by the average score. A more detailed assessment may capture nuances in relationship quality that this brief measure could not detect.

Measuring oxytocin presents technical challenges. The method used may have detected related peptides besides the hormone itself, which could affect accuracy.

The discoveries carry a message that goes beyond scope. Emotional support in marriage appears to be linked to brain function, hormone levels, and gut chemistry in ways that can affect multiple aspects of health.

The dorsolateral prefrontal cortex, the brain region that shows different patterns of activity based on social support, is involved in many forms of self-regulation other than eating. Researchers have already linked this to mood, stress responses, and decision-making in other studies, which partly explains the interest sparked by this discovery. However, this study only examined brain activity related to eating.

The intestinal changes observed in individuals with less social support involve pathways associated with inflammation and immune function. Although the study focused on obesity, these same metabolic systems are active in other health conditions, making social communication worthy of further research.