Abdominal obesity was defined as a waist of more than 89 centimeters (35 inches) in women and more than 102 centimeters (40 inches) in men. During the 12 years of the study period, the average waist size of Americans grew to 96 centimeters (38 inches) for women and 102 centimeters (40 inches) in men. "Rising concern. No doubt," said Dr. William Dietz, an obesity expert who previously worked with the Centers for Disease Control and Prevention (CDC) and now works at the George Washington University. The growth of the stomach occurs among Americans even as the overall level of obesity, which is defined not by waist size, but by the body mass index (BMI), a ratio of weight and stature has remained constant. "What this indicates is that even though obesity rates may remain stable, fat distribution may be changing, which means that we should not be complacent about this plateau" statistics, said Dietz, who was not involved in the study . 

Dr. Earl Ford, a CDC researcher and lead author of the study, said the seemingly contradictory trends are disconcerting. He said it could be that Americans are exercising less and are becoming flabby. Because fat weighs less than muscle, not necessarily are becoming heavier.  The study cites other possible reasons for the increase in abdominal fat, such as sleep deprivation and certain medications. In addition, the researchers said the increase could be related to pesticides, plastic additive BPA and other chemicals that mimic hormones that can affect weight. However, that connection is conjecture and has not been shown. Belly fat not only makes the body of some people take the shape of an apple, but it often means that ?? fat has accumulated deep inside the body, around the liver and other abdominal organs.