Our desire to eat fatty foods could be due to a connection between the gut and the brain . As researchers from the Columbia Zuckerman Institute publish in the journal Nature , in the case of mice, the fat that reaches the intestines triggers a signal. This signal is transmitted to the brain through the nerves and causes the desire to eat fatty food. The study opens the door to the possibility of interfering with this gut-brain connection, to cut off the desire for more fat, help make healthier choices, and address the growing global problem caused by overeating in some parts of the Earth.
“We live in unprecedented times, in which excessive consumption of fats and sugars is causing an epidemic of obesity and metabolic disorders ,” said first author Mengtong Li. “If we want to control our insatiable desire for fat, science is showing us that the key pathway that drives these cravings is a connection between the gut and the brain.”
Previously, researchers studied the case of sugar. They found that glucose activates a specific circuit between the gut and the brain that communicates with the brain in the presence of gut sugar. Non-calorie artificial sweeteners, on the other hand, don’t have this effect, which probably explains why diet soda can leave us feeling unsatisfied.
“Our research shows that the tongue tells the brain what we like, that is, what tastes sweet, salty or fatty,” says Dr. Zuker, who is also a professor of molecular biochemistry and biophysics and of neuroscience at the College of Vagelos Physicians and Surgeons of Columbia. ” The gut, however, tells our brain what we want , what we need.”
In the current study, the researchers wanted to see how the mice responded to the fat present in the diet, that is, to the lipids and fatty acids that we all need to live. The animals were offered bottles of water that had dissolved fats and bottles of water with sweet substances that do not affect the intestine but are attractive. In just two days, the rodents showed a preference for water bottles that had fats in them . They kept it even when scientists genetically modified them so they couldn’t taste fat. “Even though the animals couldn’t taste the fat, they were driven to consume it,” says Dr. Zuker.
The researchers thought that fat must activate specific brain circuits that drive the animals’ preference for fat. To find these communication pathways, they measured brain activity in mice while they ate fat. What happened was that neurons in the caudal nucleus of the solitary tract, or cNST, which are located in the brainstem, the most primitive part of the brain, were activated. Something that also happened in the previous study of sugar. Neurons in the vagus nerve, which links the intestine to the brain, also moved when the mice had fat in their intestines.
Next, the researchers focused on the intestine, more specifically on the endothelial cells that line it. Two groups of cells were found to send signals to neurons in the vagus nerve in response to fat.
“One group of cells functions as a general sensor for essential nutrients, responding not only to fats, but also to sugars and amino acids,” explains Li. “The other group responds only to fat, potentially helping the brain distinguish fat from other substances in the gut.”
After the findings, the scientists blocked the activity of these cells by administering a drug to the mice. None of the cell groups signaled anything, and the vagus nerve neurons did not respond to the fat in the intestine. Using genetic techniques, these vagal neurons were also deactivated. In both cases the mouse lost interest in fat. “These experiments provide novel strategies for changing the brain’s response to fat and possibly behavior toward food,” Li said.
Global obesity rates have nearly doubled since 1980. “Excessive consumption of cheap, highly processed foods high in sugar and fat is having a devastating impact on human health, especially among low-income people and in poor communities. color,” Dr. Zuker said. “The better we understand how these foods hijack the biological machinery underlying taste and the gut-brain axis, the more opportunities we have to intervene.”
Reference: Li, M., Tan, HE. Et al. 2022. Gut-brain circuits for fat preference. Nature. DOI: 10.1038/s41586-022-05266-z
