Holiday celebrations often revolve around eating, but for those with food restrictions, that can produce an incongruous feeling when dining with friends and loved ones: loneliness.

People with restricted diets -- due to allergies, health issues or religious or cultural norms -- are more likely to feel lonely when they can't share in what others are eating, new Cornell University research shows.

"Despite being physically present with others, having a food restriction leaves people feeling left out because they are not able to take part in bonding over the meal," said Kaitlin Woolley, assistant professor of marketing in the Samuel Curtis Johnson Graduate School of Management and lead author of the research.

Across seven studies and controlled experiments, researchers found that food restrictions predicted loneliness among both children and adults.

The research also offers the first evidence, Woolley said, that having a food restriction causes increased loneliness. For example, in one experiment, assigning unrestricted individuals to experience a food restriction increased reported feelings of loneliness. That suggests such feelings are not driven by non-food issues or limited to picky eaters, Woolley said.

"We can strip that away and show that assigning someone to a restriction or not can have implications for their feeling of inclusion in the group meal," she said.

Further evidence came from a survey of observers of the Jewish holiday of Passover. When reminded during the holiday of the leavened foods they couldn't enjoy with others, participants' loneliness increased. Yet, within their own similarly restricted group, they felt a stronger bond.

Bonding over meals is an inherently social experience, Woolley notes. In previous research, she found that strangers felt more connected and trusting of each other when they shared the same food, and eating food from the same plate increased cooperation between strangers.

But when restricted from sharing in the meal, people suffer "food worries," Woolley said. They fret about what they can eat and how others might judge them for not fitting in.

Those worries generated a degree of loneliness comparable to that reported by unmarried or low-income adults, and stronger than that experienced by schoolchildren who were not native English speakers, according to the research. Compared with non-restricted individuals, having a restriction increased reported loneliness by 19%. People felt lonelier regardless of how severe their restriction was, or whether their restriction was imposed or voluntary.

The study concluded that food restrictions and loneliness are on the rise and "may be related epidemics," warranting further research.

To date, Woolley said, children have been the primary focus of research on the effects of food restrictions. A nationally representative survey she analyzed from the Centers for Disease Control did not track the issue among adults.

But increasingly, she said, food restrictions are being carried into adulthood, or adults are choosing restricted diets such as gluten-free, vegetarian and vegan for health or ethical reasons. Up to 30% of all participants in her research deal with restrictions, Woolley said.

"This is a problem that I don't think people are quite aware of," she said, "and that has implications for people's ability to connect with others over eating."