Eating a high-fat/calorie diet on a regular basis may impair the brain’s capacity to control calorie intake. According to new research in rats, the brain adjusts to what is swallowed and decreases the amount of food taken to balance calorie intake after brief durations of being fed a high-fat/high-calorie diet.
The researchers from Penn State College of Medicine in the United States believe that astrocytes (huge star-shaped cells in the brain that govern many different activities of neurons in the brain) control the signalling channel between the brain and the stomach in the short term. Consuming a high-fat/calorie diet on a regular basis appears to impair this signalling system. The findings were reported in the journal The Journal of Physiology.
Understanding the function of the brain and the complicated mechanisms that contribute to overeating, a behaviour that can lead to weight gain and obesity, could aid in the development of treatments. Obesity is a worldwide public health issue linked to an increased risk of cardiovascular disease and type 2 diabetes. In England, 63% of adults are deemed overweight, with over half of these suffering from obesity. One in every three youngsters who complete elementary school is overweight or obese1.
Dr. Kirsteen Browning of Penn State College of Medicine in the United States stated,
“Calorie intake seems to be regulated in the short-term by astrocytes. We found that a brief exposure (three to five days) of a high fat/calorie diet has the greatest effect on astrocytes, triggering the normal signalling pathway to control the stomach. Over time, astrocytes seem to desensitise to high-fat food. Around 10-14 days of eating a 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.”
When high-fat/calorie diet is consumed, astrocytes first respond. When they are activated, gliotransmitters are released, which are substances (including glutamate and ATP) that excite nerve cells and allow normal signalling pathways to stimulate neurons that govern how the stomach operates. This ensures that the stomach contracts properly in response to food going through the digestive system.
The cascade is disturbed when astrocytes are suppressed. The reduction in signalling molecules causes digestion to be delayed because the stomach does not fill and empty properly. The rigorous study included behavioural observation to track food consumption in rats (N=205, 133 males, 72 females) fed a control or high fat/calorie diet for one, three, five, or fourteen days.
To target specific brain circuits, this was supplemented with pharmacological and specialised genetic techniques (both in vivo and in vitro). The researchers were able to directly suppress astrocytes in a specific region of the brainstem (the posterior section of the brain that links the brain to the spinal cord), allowing them to examine how individual neurons responded while the rats were awake.
Human research will be required to confirm whether the same mechanism exists in people. If this is the case, more research will be needed to see if the process can be safely targeted without disturbing other brain networks.
The researchers intend to investigate the process further. According to Dr. Kirsteen Browning,
“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.”
