Researchers from Penn State College of Medicine, US, found that after being continuously fed a high fat/high calorie diet, the brain adapts to what is being ingested and forgets to balance calorie intake. The study proves junk foods are endocrine disruptors, say experts
Next time you pop that biscuit absent-mindedly or reach out for the packet of chips out of habit while hammering away at your keyboard, know that you are not only loading up on calories, you are also delaying their digestion as fatty, junk foods dull your gut responses. Continuously eating a high fat/calorie diet can reduce the brain’s ability to regulate food intake, as it seems to disrupt the signalling pathway between the brain and the gut, according to new research. In short, mindless snacking rewires the brain and reduces its ability to regulate appetite or switch on the satiety button.
The study on rats, published in The Journal of Physiology, found that after being continuously fed a high fat/high calorie diet, the brain adapts to what is being ingested and forgets to balance calorie intake. Researchers from Penn State College of Medicine, US, suggest that calorie intake is regulated in the short-term by cells called astrocytes (large star-shaped cells in the brain that regulate many different functions of neurons) that control the signalling pathway between the brain and the gut. “Continuously eating a high fat/calorie diet seems to disrupt this signalling pathway,” Dr Kirsteen Browning, Penn State College of Medicine, US, lead author, said. Astrocytes stimulate neurons that ensure the stomach contracts correctly to fill and empty in response to food passing through the digestive system. When they go awry, this natural process gets disrupted. “After 10-14 days of eating a high fat/calorie diet, these astrocytes 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,” the researchers have said. However human studies will need to be carried out to confirm if the same mechanism occurs in humans, they add.
This finding is important because it nails the reason why we become gluttons and could encourage development of anti-obesity pills that target neurons.
Explains Dr Uday Phadke, Director of Diabetes and Endocrine Services, Sahyadri Group of Hospitals, Maharashtra, “Normal hunger is when one has not eaten for a long time and the body is craving for energy. This typical metabolic hunger triggers certain hormones in the gut that signal the brain to feed the body. But when one eats foods high in carbs and fats, they activate the reward mechanism whereby the brain starts feeling nice and asks for more of this pleasurable sensation. This is called hedonic hunger. Normally, the stomach is supposed to signal the brain that it is time to stop. On the other hand, the brain derives pleasure by eating fatty and sugary foods, stops responding to small amounts and asks for more. For instance, one may have had a full dinner but is tempted to have dessert despite not being hungry. Or one may eat a burger with cheese and meat that is akin to a thousand-calorie bomb. One may feel satiated but addicted to pleasurable sensation, the brain may generate a craving for more. It has nothing to do with hunger. The sight, smell and taste of the food can make you overeat. If one is not careful, this pleasure-eating can progressively lead to obesity.” Dr Phadke advises patients about restricting calorie-dense foods. “The goal is not to stop eating but to have alternatives, say a chapati instead of a biscuit that has so many calories and fat content,” he adds.
“The research gives a scientific rationale. It’s high time that a warning should be written on all junk food preparations,” says Dr Shashank Shah, Consultant Bariatric Surgeon at Lilavati Hospital, Mumbai. “Short-term junk food load is compensated by astrocytes and hypothalamic cells but chronic exposure to junk food and excess fatty acids can induce obesity,” he adds. “The hypothalamus is the area of the brain where neuronal control of obesity occurs. Foods rich in free fatty acids increase their flow to the hypothalamus. Excess deposited fatty acids then disturb the function of astrocytes, inducing what is called reactive astrogliosis. This increases secretion of Gamma-aminobutyric acid (GABA), which impacts neurotransmitters. This also increases inflammation and destroys the ability of surrounding cells of the hypothalamus to protect the body from excess weight. The result is reduction of energy expenditure and increase in body weight, followed by all other hormonal changes of obesity,” says Dr Shah. He feels it would be interesting to understand that bariatric surgeries like bypass procedures reduce the flow of such free fatty acids to the astrocytes, reduce inflammation and obesity.
Obesity is a global public health concern because it is associated with increased risk of cardiovascular diseases and Type 2 diabetes. According to Unicef’s World Obesity Atlas for 2022, India is predicted to have more than 27 million obese children, representing one in 10 children globally, by 2030.