A person with a body mass index (BMI) of 30 or greater is considered obese. BMI is calculated as weight in pounds divided by height in inches squared and multiplied by 703.
Even the most seemingly well-adjusted women still have issues with their body image, a new study suggests.
The results show women who have a normal perception of body image based on psychological screening tests still have brain scans that reveal they are concerned about getting fat.
"Even though they claim they don't care about body issues…their brains are showing that it really bugs them to think about the prospect of being overweight," said study researcher Mark Allen, a neuroscientist at Brigham Young University in Provo, Utah.
The pattern of brain activity is similar, though not as strong, as that seen in women with eating disorders such as anorexia, the researchers say. On the other hand, brain scans of men included didn't show any indication that they were concerned about body image.
The contrasting results between the sexes is likely due to the social pressure women feel to be thin in today's society, and not due to a biological difference, the researchers say.
"It's not really a male-female difference, so much as it's the social pressure that surrounds men and women," Allen said.
Body image in the brain
The study involved 10 normal-weight women and nine normal-weight men between the ages of 18 and 30. Both groups were shown images of people with different body shapes (either fat or thin) that matched the subjects' gender. With each image, the subjects were asked to "imagine someone is saying 'your body looks like hers/his." This all occurred while the subjects had their brains scanned using functional magnetic resonance imaging (fMRI).
When women looked at images of overweight individuals, their brain scans showed a spike in activity in a region thought to be involved in self-reflection and evaluation of self-worth, called the medial prefrontal cortex. Anorexic and bulimic women also show increased activity in this region when they look at images of overweight individuals, Allen said, but their brain activity is more pronounced.
The same spike in brain activity wasn't found when women pictured themselves as thin. And men showed no change in activity in this brain area regardless of whether they pictured themselves as fat or thin, suggesting they didn't experience the same self-reflection that women did.
Previous work by Allen and his colleagues has shown that male body builders that completed this experiment have brain activity patterns similar to bulimic women.
"[That's] interesting because they kind of have that same social, cultural mindset that many young women do — this over-concern with being fit and being trim — so they were really affected by those fat images," Allen said.
Overall, the results should caution women about the risks of crossing the line from concern about body image into a full-blown eating disorder, Allen said.
The current study cannot distinguish whether the spike in brain activity was due to negative feelings about being overweight, or simply the fact that these normal-weight women needed to picture themselves in a different way when they were asked to imagine themselves as fat.
In other words, researchers might see the same spike in brain activity when overweight women look at images of thin women, because picturing themselves as thin requires that they alter their self-image.
In order to tease out an answer, future studies will need to include overweight women.
The results will be published in the May issue of the journal Personality and Individual Differences.