The obese seem to be caught in a vicious circle. They respond more readily than others to fatty meals, according to findings presented at the 75th Annual Scientific Meeting of the American College of Gastroenterology held in San Antonio, Texas recently.
Thus gastric function, as well the activities of the autonomic nervous system that regulates digestion, are impaired in obese individuals in both fasting and fed states, according to a study from the University of Texas Medical Branch in Galveston, "Altered Postprandial Gastric and Autonomic Functions in Obese Subjects."
When the autonomic system is impaired or altered, the brain may not be fully informed of the food ingestion, leading to over-eating.
Measures of gastric myoelectrical activity (GMA) by electrogastrography and of heart rate variability on electrocardiogram for 12 obese and 12 lean patients were compared for a 30 minute fasting period and then 30 minutes after a fatty soup or a high protein soup.
"Obese subjects in the study showed enhanced responses to both soups," said the study's co‐author Jiande Chen, Ph.D. "The obese were more receptive to fatty meals, meaning the stomach is more tolerant to fatty meals, as well as more responsive to protein meals. Since the function of the stomach is to pump whatever is in the stomach to the small intestine, being more responsive means that the stomach may empty the protein meals more quickly in obese subjects than in lean subjects," explained Dr. Chen.
Researchers observed that the percentage of normal slow waves was reduced with the fatty soup in the lean group, but not in the obese. The power of gastric slow waves was not altered with the protein soup in the lean, but increased in the obese.
According to Dr. Chen, "Obese patients are more prone to fatty meals. The stomach of lean subjects gets 'sick' (a reduction in normal slow waves of the stomach) with fatty soup, whereas the stomach of obese subjects is fine with fatty soup. The increase in the power of gastric slow waves with the protein soup in obese, but not in lean, suggests that the stomach responds to protein soup more positively and the emptying of the stomach may be faster in obese than in lean."
Additionally, researchers found reduced activity for the vagus nerve that regulates muscle contraction of the stomach and intestines to help process food among obese subjects in the study, and increased activity in the sympathetic nervous system in the fasting state.
The obese demonstrated a complete absence of normal autonomic responses after eating. "Typically, after a meal in lean subjects, the cardiac sympathetic activity increases and the cardiac vagal activity decreases," said Dr. Chen. "In the obese subjects, however, these normal post‐meal changes in the cardiac autonomic functions were completely absent, which suggests an impaired autonomic response to food ingestion. The autonomic nervous system sends meal‐related gastrointestinal information, such as mechanical distention and chemical stimulation via nutrients to the brain. If the response of the autonomic system to food ingestion is impaired or altered, the brain may not be fully informed of the food ingestion, which may lead to over‐eating," explained Dr. Chen.