Physical activities do not reduce the desire to eat in obese women

Published on July 4, 2008 5:38 AM

Researchers at the University of Michigan have found that exercise does not cut the appetite in obese women, as it does in lean women.

Though we all use the terms "fat" and "obese" casually in conversation, there is a medical definition of the condition and yes, obesity is considered a health "condition." "Obesity" specifically refers to an excessive amount of body fat. As a rule, women have more body fat than men. Most health care professionals agree that men with more than 25 percent body fat and women with more than 30 percent body fat are obese. These numbers should not be confused with the body mass index (BMI), however, which is more commonly used by health care professionals to determine the effect of body weight on the risk for some diseases.

"The lack of appetite suppression may promote greater food intake after exercise in obese women," said Katarina Borer, PhD, a University of Michigan researcher.

Borer found that in the people organisms a hormone called leptine, which in animals curbs appetite when body fat increases. When leptin levels rise, it supposedly shuts off appetite and motivates physical activity to burn calories. However, as obese people become fatter, their leptin levels rise, but they become resistant to the actions of this hormone.

"The hormone doesn't do the job it's supposed to do in lean people," Borer added.

Borer's group studied 20 postmenopausal women: 10 lean and 10 obese women. The women ate three weight-maintenance meals a day while participating in three experiments on three separate days. During one experiment they did not exercise.

In the other two experiments the women exercised on a treadmill in the morning and the afternoon. They burned 500 calories each time, for a total of 1,000 calories a day. These two experiments differed by exercise intensity. One involved walking at high intensity, or 80 percent of maximal effort, for 7.5 minutes, with 10-minute rest periods between 10 walking sessions. The other experiment was half as intense and involved walking for 15 minutes and resting for 5 minutes.

Every hour and before each meal, these women recorded their appetite level on a 10-point scale ranging from not at all hungry to extremely hungry. Blood samples were collected every 15 to 60 minutes for hormone measurements.

Obese women affirmed they were less hungry than lean women before meals and reported no appetite suppression during exercise.

Scientists found that obese women had much higher leptin levels than in lean women. But during intense exercise, obese women did not have reduced production of leptin, as lean women did, but only moderate-intensity exercise lowered leptin in obese women.