Gut Hormones Influence Eating, Addictive Behaviors
What’s in your guts might influence how your brain responds not only to food, but also to alcohol and cigarettes, claimed Dr. Tony Goldstone at an NIH psychoneuroendocrinology scientific interest group lecture in the Clinical Center.
Several gut hormones, including ghrelin, PYY, GLP-1, and insulin influence the brain’s response to food, he explained. These hormones send signals to areas of the brain responsible for eating and addictive behaviors.
“When you’re hungry, you’re liable to find high-energy foods more appealing,” said Goldstone, head of the psychoneuroendocrinology research group at Imperial College London, based at the Hammersmith Hospital in London, U.K.
An empty stomach produces ghrelin, referred to as the “hunger hormone.” Ghrelin signals the brain to feel hunger. After a person eats, the intestines produce hormones such as GLP-1 and PYY that ease the sensation of hunger.
In several studies, Goldstone has observed that when volunteers were shown photos of hamburgers, pizza, cake and other high-energy dense foods on an empty stomach, activity increased in the areas in the brain that respond to reward. The opposite happened when patients were full. Reward centers were less active when the volunteers viewed photos of high-energy foods. The effects of fasting could be mimicked by giving injections of the hormone ghrelin.
He also studied patients who have had gastric bypass surgery, a procedure for obesity in which parts of the stomach and intestines are reconnected so that food bypasses most of the stomach and the first part of the small bowel. After the surgery, Goldstone said, patients respond less to photos of high-energy foods than do patients with obesity who have not had surgery, or after a different type of surgery called gastric banding. The appeal of high-energy foods declines after gastric bypass surgery, as does the associated activation of the brain reward system, while the appeal of low-energy foods, such as vegetables, stays the same.
In fact, the intestines of patients who have had gastric bypass surgery produce more GLP-1, a hormone that reduces blood sugar and causes a reduction in appetite, and PYY, a hormone that also reduces appetite. The changes in these hormones are in part responsible for the beneficial effects of this surgery and appear also to explain these healthy changes in food reward.
In addition to altering how the brain responds to pictures of food, nutritional state might also influence other addictive behaviors, including how people respond to money and stress, how impulsive they are or the risks they take.
In one study, Goldstone’s team told healthy volunteers they could win money if they pressed a button at a correct time. When volunteers had not eaten overnight and were hungry, their brain’s reward centers showed more activity while they were anticipating winning money than when they were full. This study also found that when volunteers were shown unpleasant photos that produced discomfort, their brains were more responsive if they hadn’t eaten.
“Food intake suppresses the brain’s responsiveness to unpleasant images,” he explained. “We have also seen this happen after gastric bypass surgery, suggesting that changes in gut hormone may be responsible for this effect.”
In animal studies, the gut hormones GLP-1 and ghrelin have been shown to “modify reward behaviors to almost any drug tested.”
Currently, Goldstone is studying patients who are trying to lose weight and others who have recently quit drinking alcohol or smoking cigarettes, as part of the Gut Hormones in Addiction study (www.ghadd.ac.uk). “We are investigating whether manipulation of these GLP-1 and ghrelin hormones can reduce craving and brain responses to food, alcohol or cigarettes, as well as unpleasant images.” He hopes to publish his findings soon.
“These gut hormones are targets towards treating obesity, but also may be effective in preventing cravings and reducing consumption and relapse in populations such as alcoholics and smokers,” he concluded.