A recent study found that junk food may alter the brain's neurological pathways, reducing its ability to regulate caloric intake. According to the researchers, the mechanism that fatty foods sparks on neural activity could not only lead to overeating, but also to obesity.

A new study in the Journal of Physiology suggests that junk food reduces the brain's ability to regulate caloric intake by altering neurological pathways, and subsequently disrupting appetite in the long term, which could lead to overeating and weight gain.

Researchers at Penn State College of Medicine in the United States arrived at this conclusion after conducting research that subjected rats to a high-fat, high-calorie diet for 14 days. They observed that the rats' astrocytes (cells in the brain that regulate neuron functions including the pathway between brain and gut) became desensitized with continuous fat consumption.

These star-shaped cells act as intermediaries between the brain and the stomach and signal chemical transmitters that determine how the stomach works. During the first four days of the study, no abnormalities were noticed in the brain or stomach. However after fourteen days, the researchers discovered a decrease in astrocyte activity in the rats, which disrupted digestion and appetite.

"Calorie intake seems to be regulated in the short-term by astrocytes. We found that a brief exposure (three to five days) of high fat/calorie diet has the greatest effect on astrocytes, triggering the normal signalling pathway to control the stomach. Over time, astrocytes seem to desensitize to the high fat food.

Around 10-14 days of eating high fat/calorie diet, astrocytes seem to fail to react and the brain’s ability to regulate calorie intake seems to be lost. This disrupts the signalling to the stomach and delays how it empties," explained Dr Kirsteen Browning, main study author, in a press release.

Normally, the brain has the ability to adapt to respond to what is ingested, and reduces the amount of food consumed to balance the caloric intake. Astrocytes initially respond when high-fat, high-calorie foods are ingested.

Their activation triggers the release of gliotransmitters, chemicals that excite nerve cells and activate normal signaling pathways to stimulate the neurons that control stomach function. The release of gliotransmitters allows the stomach to contract to fill and empty itself after food has passed through the digestive system.

Over time, the chemical signaling cells weaken and make digestion slower: the stomach no longer fills and empties properly.

According to Dr. Kirsteen Browning, it is still unclear whether the decrease in astrocyte activity is the cause or the result of overeating. "We have yet to find out whether the loss of astrocyte activity and the signalling mechanism is the cause of overeating or that it occurs in response to the overeating. We are eager to find out whether it is possible to reactivate the brain’s apparent lost ability to regulate calorie intake. If this is the case, it could lead to interventions to help restore calorie regulation in humans," she added.

She says the discovery of a disrupted pathway between the brain and stomach could eventually pave the way for an anti-obesity treatment.

According to a study published in the journal BMJ Global Health in September 2022, nearly two-thirds of adults worldwide are overweight or obese. By 2060, researchers estimate that three out of four adults will be affected.

Following the study on rats, the American researchers plan to further explore the action of fatty foods on the brain. Research with humans will need to take place to confirm whether the same mechanism occurs in humans. If so, additional testing will be needed to assess whether the mechanism can be safely targeted without disrupting other neural pathways.