"Women have a much stronger reaction to food, such that whether they try to inhibit their desire or not, they have stronger signal [in the part of the brain that controls hunger perception and desire to eat]," study leader Gene-Jack Wang, MD, tells WebMD.
Wang, chairman of the medical department of Brookhaven National Laboratory, Upton in N.Y., and colleagues have been using state-of-the-art brain imaging to learn which parts of the brain are involved in eating behaviors.
They have previously shown that obese people are less able than others to sense when their stomachs are full. Recently, they have looked at what happens in the brain when a hungry person gets to see, smell, and taste -- but not eat -- favorite foods.
In some of these studies, they saw very strong signals in parts of the brain involved in emotional regulation and motivation. But in other studies, the signals weren't so strong. Wang suspected this might be because of differences between how men and women react to food.
So they tested 13 women and 10 men with PET brain scans. To make sure they were hungry, study participants fasted for 18 hours before scanning. And to make sure they were tempted, the researchers made the participants' favorite foods: bacon/egg/cheese sandwiches, cinnamon buns, pizza, cheeseburgers, fried chicken, lasagna, barbecued ribs, ice cream, brownies, and chocolate cake.
During scanning, participants were able to see and smell the food. They even got tastes, applied to their tongues with a cotton swab. To make sure they stayed tempted, researchers brought them new hot food every four minutes.
But subjects didn't get to eat until the 30-minute scans were completed, and only after they completed a quiz on their feelings of hunger, desire for food, and alertness.
Before their second round of scans, participants were asked to practice ignoring the food or shifting their thoughts away from it. During this phase of scanning, they were asked "to inhibit their desire for food and suppress their feelings of hunger."
That worked pretty well for the men. Their brain scans showed much less hunger-related activity when they tried to suppress their desire for food.
That didn't happen for the women, at least not as a group. Although some women were better than some men at suppressing food desire, overall the women's brains showed just as much hunger-related activity when they tried to hold down their desire.
Are the findings plausible? WebMD asked Rexford S. Ahima, MD, PhD, director of the obesity center at the University of Pennsylvania's Institute for Diabetes, Obesity, and Metabolism. Ahima is an expert in the brain circuits responsible for feeding behavior and body weight regulation.
"More and more we see there is a structural basis for why we eat the way we do. Maybe our brains are hardwired to predetermine the way we eat," Ahima says. "The interesting thing about the Wang study is that when they present food to people and ask them to consciously inhibit the urge to eat, men are better able to do it than women."
Ahima notes that the study only shows men to be better at inhibiting their brains' response to food. But can men really resist emotional eating better than women can? That, he says, will have to be tested directly.
Sex Hormones May Affect Hunger
Why do men's and women's brains respond differently? Wang and Ahima suspect that female sex hormones play a major role.
"There is a link between female hormones tending to promote weight gain and overeating," Ahima says. "There are some women who tend to binge eat in synch with their menstrual cycles. And look at pregnancy -- it makes some women overeat, but some do not. So while there may be overall differences in terms of gender, this may differ for individuals."
Wang suggests that women may have evolved to seek food more avidly than men do.
"There could be evolutionary needs for that, because women have a very important mission: They have to carry the baby," Wang says. "And for most of human history, you could never get enough food to eat. Now that's no longer a problem in developed countries -- but now this brain circuit is a problem when we are surrounded by attractive, high-calorie foods."
The solution, Wang says, is for people who find themselves unable to control their eating to keep filling, low-calorie foods close at hand.
"Our lifestyle now is so much different from that of our grandparents," Wang says. "Our jobs and our living status is very stressful. So when we see food we eat it, because we want to do something to compensate for our problems. Inhibition control is very important -- but if you can't have it, surround yourself with nutritious foods."
Wang's study appears in the Jan. 15 early online edition of the Proceedings of the National Academy of Sciences.