Dinner by yourself can be a lonely affair. The lack of social connection could change the way that your body processes your meal.
A new study published in Science Advances has now found evidence that eating with others could help your body balance your blood sugar levels.
In experiments, 108 participants consumed just over 100 grams of white-wheat bread. For the following two hours, researchers tracked their glycemic response.
In one scenario, participants ate the bread on their own. In another scenario, they were accompanied by a close companion.
In the social scenario, blood sugar levels spiked less and returned to baseline faster than in the alone scenario.
The authors argue that this aligns with a “robust phenomenon” in humans.
“Blood sugar regulation is not just about what we eat, but who we eat with,” explains Shir Atzil from the Hebrew University of Jerusalem in Israel.
“Our relationships have an active biological role in our physical well-being.”
Atzil and colleagues argue that their findings provide a proof of concept for the principle of ‘social physiology’.
This is a biological framework for understanding how links between our inward and outward lives have evolved over time.
Social physiology could at least partly explain why we, as a species, are incentivized to cooperate: we are interdependent organisms who rely on each other for greater survival.
You can see that in our very blood, even when we aren’t physically touching.
“We used to think of the body as an isolated system that regulates itself,” explains Atzil. 
“Our findings show that human physiology is inherently social. Being close to someone you love lowers the physical energy your body spends on regulating itself. This gives us a direct metabolic benefit to being together and reveals a core evolutionary reason why humans form bonds in the first place: our bodies run better together.”
In other social animals, like fruit flies, rodents, pigs, and monkeys, studies suggest that isolation can shorten lifespans, suppress immune systems, or amplify stress reactions.
But for ethical reasons, these sorts of experiments are not conducted among humans.
Instead, researchers use small changes in how the body functions alone versus in social settings to better understand how we change in the presence of others.
Glucose responses are a clever way to do this.
When mice are kept in social isolation, studies have found it alters their insulin signaling and impairs their metabolic function, raising the risk of obesity.
In humans, by comparison, loneliness is associated with dysregulated glycemic control and predicts type 2 diabetes.
“While prior work has focused on the outcomes of social isolation, the present study identifies a direct, quantifiable benefit of social proximity in glucose metabolism,” the authors explain.
The team’s experiments compared how human bodies respond to the same carbohydrate meal when alone versus in company.
They also ran parallel experiments among 116 participants, testing how the body copes with cold exposure.
When a partner was present, the body’s temperature regulation was more efficient, especially when the two people were touching.
But even when no one was touching, there were benefits.
In another set of experiments among 115 adults and 56 mother-infant pairs, participants underwent a stress challenge.
It produced a smaller arousal response, such as increased sweating, when another person was present, even if they weren’t physically skin-to-skin.
This arousal response was also ameliorated faster when in company.
The findings suggest that having somebody close by, even if you aren’t touching, could help your body run more efficiently.
What those effects are in the long run is an open question, but population studies generally suggest that loneliness is not good for our overall health.
Evidence suggests that individuals with stronger social ties tend to be healthier, happier, and live longer.
Conversely, social isolation is associated with increased metabolic disorders, cardiovascular disease, cancer, slower wound healing, reduced sleep efficiency, and mortality.
The world’s largest study on happiness has been running for 88 years and counting.
After analyzing hundreds of peer-reviewed papers and countless questionnaires, medical check-ups, and in-person interviews with participants, researchers found that close relationships were one of the best predictors of a happy and meaningful life.
Surrounding ourselves with loved ones seems to be inherently good for us.
It could change how our bodies cope on a miniscule level, but with big repercussions.

The research has been published in Science Advances.