Obese People Experience Delay In Feeling Full, UF Researchers Find
February 26, 2003
GAINESVILLE, Fla. — Most people feel full about 10 minutes after they begin eating, but for those who are obese, it may take almost twice as long for their brains to get the message, according to researchers at the University of Florida’s Evelyn F. and William L. McKnight Brain Institute.
Through innovative use of neuroimaging, UF scientists successfully pinpointed when the brain responds to changing hormone levels in the body that signal satiety. The finding raises the possibility that a delayed feeling of fullness or the inability to feel satisfied while eating could perpetuate obesity, making treatment difficult, they report in the February issue of Psychiatry Annals.
In the same issue, UF scientists present an overview of research that says the enjoyment of highly palatable food, such as a steak dinner, may produce changes in the brain similar to those produced by cocaine and other drugs of abuse.
As for the drastically overweight who are slow to feel full, the solution may be to make behavioral changes, such as eating only when hungry, slowing the pace of meals and learning to appreciate smaller portions, said Yijun Liu, an assistant professor in the UF College of Medicine’s psychiatry department at the McKnight Brain Institute.
“My mother was right when she said that I should eat slowly,” Liu said.
Liu used a novel magnetic resonance imaging method known as temporal clustering analysis to scan the brains of 10 obese and 20 normal-weight adults. Each volunteer received about 350 scans over the course of 35 minutes, Liu said. Glucose was given to them intravenously after the first five minutes to trigger the food response. The responses to food in the hypothalamic region of the obese patients’ brains were not only weaker but also significantly delayed, taking four to nine minutes longer to occur.
Obesity accounts for more than 300,000 premature deaths each year in the United States, second only to tobacco-related deaths, according to statistics from the Centers for Disease Control and Prevention. Obesity is defined as having a body mass index of 30 or higher, usually meaning a person is about 30 or more pounds overweight.
The research lends credence to theories that the brain’s pathways for saying “when” are fewer and less developed than the pathways that prompt eating, researchers said. Further, viewed along with additional research presented in February’s Psychiatric Annals, it suggests that loss of control over eating and obesity produces changes in the brain that are similar to those produced by drugs of abuse.
“Our work suggests that Thanksgiving is the single day of the year with the least amount of drug use,” said Dr. Mark S. Gold, a distinguished professor of psychiatry and neuroscience and chief of the addiction medicine division at UF’s College of Medicine. “Who binges on turkey and then shifts focus to drug taking? Overeating has an inhibitory effect on illicit drug taking.”
Gold served as guest editor for Psychiatric Annals, presenting a package of articles by researchers from UF and elsewhere that brings home the message that overeating, obesity and insulin resistance is an increasingly significant health threat. It also presents “intriguing and cogent evidence that overeating can affect changes in the pleasure-reinforcement circuits of the brain that closely resemble those seen in addiction,” said journal editor Dr. Jan Fawcett, a psychiatry professor at the University of New Mexico School of Medicine.
Neurotransmitter changes occur in the brain whether they are provoked by natural rewards, drugs, gambling, feeding or fasting, Gold said in an accompanying journal article. The article is based on Gold’s own many years of research along with data cited in another of the journal articles from scientists at the Brookhaven National Laboratory in Upton, N.Y., who demonstrated through positron emission tomography scans that dopamine is a key neurotransmitter in alcohol and cocaine reward, as well as in food reward and overeating.
“It’s more than hypothetical that there are brain abnormalities associated with obesity,” Gold said.
The similarities between the misuse of food and drugs are striking, said Dr. William S. Jacobs, an assistant professor in the UF psychiatry department’s addiction medicine division and medical director of Gateway Community Services Inc. in Jacksonville. Both disorders involve similar brain systems and result in similar behaviors and feelings. Patients who need treatment report loss of control, compulsive use and denial. Both disorders generally involve early substance experimentation – one with drugs, the other with diets or binging. Both can result in early death.
“Patients with binge eating, obesity, anorexia and bulimia have a chronic disorder characterized by loss of control, relapse, compulsivity, shifting priorities and continuation despite severe and adverse consequences,” Jacobs said.
Gold said he hopes the ever-increasing evidence that tempting foods can be highly pleasurable and as compelling as potent drugs of abuse will help physicians to recognize their role in solving the major public-health problem presented by obesity and lack of exercise.
“Up until recently, people thought an addiction model might be an excuse for overeating, but it explains why we have an epidemic of obesity,” Gold said. “It’s important to realize that palatability has changed the way the brain processes food information. Most of us do not eat for hunger or because we’re starving. Most of us eat because it’s a pleasurable activity. The brain has a lot of pathways to reinforce eating. But those pathways for saying ‘when’ have not kept up with the abundant food supply.”
Generally, people who are obese have limited success with weight-loss programs unless they make major lifestyle changes, said Jeff Wagner, a board-certified nutritional counselor in Washington County, Pa.
“At least half of obese patients have been through numerous programs,” Wagner said. “That’s their life story – going from program to program, diet to diet. Just as only a small percentage of people succeed when they first try to break their drug habit, it’s the same with obesity. They need structured living or day-to-day intervention. It’s not a matter of the right product, program or diet. It’s a matter of admitting you have a problem and making a commitment to permanently change your behavior, which often means changing your relationships with others. Only people who are willing to work very hard are successful.”