If women are prone to "eat like a bird" when men are watching, men may be similarly programmed to "eat like a horse" when women are around, suggests a small US study by behavioural scientists.
Researchers observed diners at an all-you-can-eat Italian buffet and found men who dined with at least one woman at the table ate 93 per cent more pizza than their peers who had only male dining companions.
The tendency to overeat extended to healthier fare as well - men ate 86 per cent more salad in the company of women.
"We find that while men disproportionately over-eat in the company of women, women felt like they overate and felt rushed when eating with men even though there was no evidence that they actually ate more," said lead study author Kevin Kniffin of the Dyson School of Applied Economics and Management at Cornell University in Ithaca, New York.
"People should calm down when eating with members of the opposite sex," Kniffin added by email.
To see how mixed-sex dining might influence eating habits, Kniffin and colleagues asked 74 men and 59 women at an Italian restaurant with a menu featuring unlimited pizza, salad and sides to join them for a lunchtime experiment.
Researchers asked diners arriving at the restaurant why they chose it and whether they considered other places to distract them from the true purpose of the study, and then sat back to watch how much people ate based on who else was at their table.
Men dining with women typically ate about three slices of pizza and five bowls of salad, compared with about 1.5 slices and less than three bowls of salad when they ate in the company of other men.
The women, meanwhile, ate more salad and less pizza when joined by female companions than when dining with men.
It's possible that the men might be unconsciously signaling their biological fitness through excessive eating, essentially showing off to appear attractive to a potential mate, Kniffin said. By engaging in risky or unhealthful behaviour during the meal, the men signal that they are so healthy and fit that they can endure self-inflicted pain on a temporary basis, at least.
"In other words, 'self-handicap behaviour' is basically a kind of showing off," Kniffin said.
Beyond the small size of the study, other limitations include the lack of social context for the meals that might provide clues about how eating habits differed for a date versus a business lunch, the researchers acknowledge in the journal Evolutionary Psychological Science.
It may be a stretch, for example, to assume that men might eat more pizza in the presence of women only because they feel a need to show off, said Samantha Heller, a senior clinical nutritionist at New York University Langone Medical Center who wasn't involved in the study.
Nerves, the social setting, and who is picking up the tab all might contribute to how much men eat on dates, for example, Heller said by email.
While it's hard to make specific diet recommendations based on such a small study, overall guidelines for healthy eating can still apply when men and women dine together, Heller noted. Following a plant-based diet most of the time, though, might help supersede the high intake of pizza and burgers on occasion.
"We should all be eating more slowly, mindfully and thoughtfully," Heller said. "There is never any reason to stuff one's self into a food coma. It's tough on the body in many ways and never leaves one feeling energized, healthy, or in the case of the male-female relationship, sexy."