How Eating Releases Opioids in the Human Brain
Research shows that endogenous opioid release occurs even in the absence of pleasure, meaning people may binge eat even when food doesn’t taste good.
Whether it’s the holiday season or someone’s birthday in the office, it’s hard not to overeat when you’re surrounded by delicious food. But what if you’re surrounded by bland, tasteless food? It might be just as hard to say no.
Researchers from the Turku PET Center in Finland found that when people drank a tasteless nutritional drink their brains released more opioids, the chemicals linked to pleasure and euphoria, than when they ate a piece of pizza. The study suggests that opioid release in the human brain may not always be linked to the experience of pleasure, but can still leave you wanting more of whatever gave your brain that endorphin rush.
“This finding leads us to think that maybe opioid release during eating is not so much related to pleasure but to satiety itself,” said Lauri Tuominen, research fellow in psychiatry at Massachusetts General Hospital and co-author of the study.
During the study, participants were injected with a radioactive compound that was bound to their brain’s opioid receptors. Radioactivity in the brain was then measured using positron emission tomography (PET) scans under three different circumstances: after eating pizza (a palatable meal) after consuming a nutritional drink (a non-palatable meal), and after an overnight fast.
Unsurprisingly, participants described feelings of pleasure when eating the pizza but not when consuming the nutritional drink. What amazed the researchers is that even though the participants felt no pleasure when consuming the nutritional drink, it still caused more of an opioid release in the brain than the pizza.
“The finding that something as tasteless as a nutritional drink would release opioids was a surprise to us,” Tuominen said, explaining that this opioid release could mean bad news for portion control, especially for people who already overeat. “For binge eaters, food does not need to taste good and they may still binge it,” Tuominen commented.
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The study did not test whether the rate of food absorption played a role in opioid release but Tuominen would like to consider this in future trials.
“In this experiment, we did not measure metabolism directly, but it’s interesting that nutritional drink is absorbed faster than pizza from the gut,” he said. “The brain and particularly the opioid system may respond differently depending on the speed that the food is absorbed.”
The human opioid system regulates our appetite and previous research has shown that a dysfunctional opioid system is a major sign of morbid obesity. The results of the PET Center study indicate that overstimulation of the opioid system may be to blame. Tuominen and his team are exploring how this information can be used in weight management and obesity prevention.
“At the Turku PET Center we are currently investigating whether the activity of the opioid system could predict who is at risk for obesity,” Tuominen said. “The study also highlights the role of the opioid system in eating and as a potential target for novel treatments.”
One of these novel treatments might include the administration of naloxone, an opioid blocker used to treat opioid drug overdoses, to slow the rate of food consumption. A 2011 study discovered rats undergoing morphine withdrawal ate less food when they were given naloxone. Tuominen hopes his study will inspire other researchers to investigate the use of opioid blockers in obesity prevention.
“There are some data showing that Narcan (a naloxone nasal spray) could be used to treat obesity and this study hopefully encourages further look into that kind of treatment.”
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