We’ve all been there. What starts as a handful of chips or a spoonful of ice cream ends with an empty container and dread of the bathroom scale. But what is it about food that makes even the most disciplined person occasionally overeat?
For years, researchers have been probing the possibility that obesity and addiction overlap, with emerging evidence suggesting that the same reward circuits in the brain that are activated by drugs also respond to calories. Obese people, the thinking goes, may overindulge because their brains’ reward circuitry, which responds to the pleasure of eating, is out of whack.
Now, Yale University researchers have found evidence that high-fat foods have the ability to alter and interfere with the reward circuitry in the brains of mice — and that injecting a particular molecule can restore the normal reward response in the brain. Administering that molecule can even cause mice to find a low-fat meal satisfying.
“The idea is that if the brain adapts to a drug or calories in such a way that your reward response is deficient, then these individuals would need to consume more of the same,” said Ivan de Araujo, a professor of psychiatry at Yale University School of Medicine, who led the study published Thursday in the journal Science. “When the reward system is weak, you do more to obtain the same reward.”
The researchers first tested how calories from high-fat food activated reward circuits in the brain, independent of the pleasure animals experience from tasting and smelling food. They used a catheter to infuse high- and low-fat foods directly into the animals’ guts, and found that the high-fat calories caused deficient responses in the brains’ reward circuitry.
Then they injected a molecule normally released in response to fat intake, called oleoylethanolamine. Doing so restored the levels of a neurotransmitter, called dopamine, involved in the brain’s reward responses. Mice on a high-fat diet given the molecule were also able to find low-fat meals more satisfying.
Now, the researchers hope to monitor the brain activity of human subjects using imaging scans, to see whether they can alter activity in the brain’s reward circuitry through a similar treatment. They are also interested in studying whether some of bariatric surgery’s positive effects may be explained by alteration of this same brain-gut signaling pathway. They have yet to study whether other components of diet, such as sugar, act through the same mechanism.
Dr. Nora Volkow, director of the National Institute on Drug Abuse, who was not involved in the research, said it was a fascinating elucidation of the ways in which a peripheral organ is linked to the reward pathways in the brain.
“What has been surprising is that there’s been such a reticence to recognize this,” Volkow said. “You have different levels of severity. . . . I lose control once in a while with candies or with chocolate — it does not mean I am addicted. Drugs activate and hijack the neurocircuitry that is in our brain to respond to natural rewards like food.”