According to the Daily Mail, women eat less with a man present than they would with a woman. When eating in a group, women ate less the more men there were. "But," writes an unnamed Daily Mail reporter, "when in all-female groups women pigged out and consumed more calories - reinforcing the image of an indulgent girls' night in with ice cream and chocolate."
In a slightly more sober and detailed (than the Daily Mail? No!) writeup for WebMD, Kathleen Doheny quotes study author Meredith Young:
"Women in groups of women tended to increase the caloric value of the food they choose," she says, compared to eating alone or with men. "The bigger the group of women, the more they eat," she says. For instance, women who ate in a group of three each ate about 650 calories, while those who ate in a group of four averaged about 800 each.
Young hypothesizes that women may eat less in front of a man "to look more feminine and in control." Doheny writes,
women want to look more attractive, especially if a potential date or mate is sitting at the table. Other research, Young says, has found that women who eat less are viewed as more attractive and that thin women are seen as more attractive.
It's not really a surprise that women still buy into the stereotype that eating a lot in front of the man is unfeminine (although it is possible that some women eat less with men out of sheer nervousness). But the Daily Mail's "indulgent girls' night" and Doheny's headline — "Ladies' Night Out a Diet Wrecker" — are a bit simplistic. Is it necessarily worse to eat more when you're with your girlfriends? Sure, there's the old trope of women goading each other into ordering dessert (and the equally popular trope of looking down on each other for eating it), but not every meal shared with women is an eating-disordered binge-fest. Some variance in how much we eat at each meal is normal, and while Young's advice — "I suggest it's just something to be aware of" — is pretty measured, it seems unnecessary and unfun to raise your diet-guard every time you go out with your friends.
Young found that men didn't change their intake no matter who their eating partners were. The Daily Mail says, "men simply eat what they want no matter who they are with." What a novel idea.