Ladies' Night Out a Diet Wrecker

Aug. 5, 2009 -- Girls' night out can be fun for single and married women alike, but eating with a large group of women friends may influence you to eat more, a new study suggests.

"Women eating in groups of women tend to increase the calorie values of the food they choose," says Meredith E. Young, PhD, a psychologist and an assistant professor in the Centre for Medical Education at McGill University in Montreal, who led the study.

Women who eat in smaller groups of women friends, she found, eat somewhat less, and those who eat a meal with a man eat even less.

For the men, Young found a different story. Neither the number of dining companions nor the group's gender makeup seemed to make a difference in how much the men ate.

The study is published online in the journal Appetite.

Young and her colleagues observed 469 college men and women eating at three different cafeterias at McMaster University in Hamilton, Ontario, Canada, where Young completed the research.

The researchers observed which food items students placed in front of them at the tables, tallied the calories, noted the sex of the people dining, and recorded the size of the groups.

Next, the researchers analyzed what factors affected food intake, such as the sex of dining companions and the size of the group.

Calorie Intake: Men vs. Women

Not surprisingly, Young's team found that total calories were higher for men's meals than for women's. Men averaged about 716 calories while women averaged 609.

When women ate with men, they took in about 552 calories, but when eating with another woman, took in more, about 665.  When two men or two women ate together, they ate about the same number of calories.

"When it is a date situation, that's when we see a big difference," Young says.

When a woman eats with a mixed group, Young found, she also eats less than when she eats only with other women. "As soon as there is a man in the mix, the amount of calories a woman eats decreases."

As the number of men in the group increased, the calorie count in the women's meals decreased, she found.

"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.

But the sex of dining companions or group size didn't influence caloric intake for men, she found. "Men didn't seem to be affected by anything," Young tells WebMD.

Exactly why dining companions of the opposite sex influence how much women eat isn't known, Young says, although she can speculate.

"The hypothesis we'd like to keep right now is, the social signaling thing," she says. In other words, 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.