For seven days, the subjects ate a weight-maintaining diet. Then one morning, no breakfast was served and nothing again all day. The next morning, after thirty-six hours without food, the subjects were taken to a room for a brain scan using positron emission tomography, a mapping of the cerebral blood flow that reveals which areas are being activated.
Note:This is an excerpt from the book "Hunger: An Unnatural History" by Sharman Apt Russell (Basic Books, 2005), pg 27.
In Angelo Del Parigi’s experiment, men and women did not show any significant differences in how they rated feelings of hunger and satiety. There were no differences in the appetite centre in the lower brain, which regulates the balance between hunger and satiety and its effect on body weight. There were no differences in the chemical and hormonal signals sent through the blood, except for lower levels in women of a hormone that inhibits hunger. But hungry men had more activity than women in the area of the brain that processes emotion, as if they felt their hunger more acutely. And satiated men had more activity than women in the part of the brain that processes the association between stimulus and response, in short, the feeling of satisfaction: hey, that was good! Satiated women had more activity than men in the occipital temporal cortex, the seat of object recognition. No one knows yet what this means.
Not just once, but many times, Angelo had asked people not to eat so he can watch their brains light up. Other experiments with thirty-six hours of fasting were between lean and obese men and lean and obese women. Obese individuals responded to satiation with greater activity in their prefrontal cortex, an area associated with complex thought and the inhibition of “inappropriate response tendencies” and decreased activity in the lower brain area associated with emotion. Does this suggest that obese people respond to eating and satiation with more social and cognitive inhibitions perhaps learned and acquired? Do they get less emotional reward from eating? Again, we don’t know, and Angelo won’t speculate.
But these studies are also practical. Women suffer more from obesity and eating disorders than men, so it is useful to know if there are gender differences in how women and men respond to hunger. For people trying to diet, it is useful to know how they will react to calorie deprivation and weight loss. The problems associated with obesity make it one of the biggest health threats of the twenty-first century, on the World Health Organization’s top ten list, on the top five list for developed countries. The morbidly obese can suffer horribly. Even the mildly obese risk shorter lives.