Sugar and fat are two ingredients that are almost always present in addictive foods. Carbonated drinks, juices, sweets or chocolate bars are loaded with sugar. Menus at fast-food restaurants rely on our appetite for fat to make their products attractive. The taste of these foods is important… but according to a new study published in Nature, there is more to it than that. A signaling system exists in humans, facilitating communication between the brain and the gut. This may help explain the urge behind one of humanity’s major health problems.
“These results support the idea that there are two sensory inputs going to the brain: one encodes what we like and the other what we want. These two inputs work together. First, with the tongue, you recognize what you like… but then the stomach tells you what it needs,” explains Charles Zuker, a researcher at the Howard Hughes Medical Institute and a professor at Columbia University.
This division could explain, according to a 2020 study on sugar, why drinks with artificial sweeteners fail to match the attraction produced by those with real sugar. In that study – also published in Nature – it was observed that, even in mice whose sense of taste had been suppressed, the preference for drinks that included sugar over artificially sweetened beverages was maintained.
In the case of fat, the team led by Zuker tested the mechanisms that determine food preferences, providing two types of substances (dissolved in water) to laboratory mice: one had fat, while the other, though artificially sweetened, was non-fat. Within two days, the mice showed a clear preference for greasy, fatty water, even when the researchers genetically modified them so they couldn’t taste fat on their tongues. This proved that the desires of the intestine could, in fact, trump the tongue.
María del Mar Malagón, president of the Spanish Obesity Society and professor at the University of Córdoba, considers the new research to be “extraordinary.” For her, the most interesting aspect is that “researchers have been able to delimit the brain area that is activated when eating fat, [which] is responsible for the appetite or preference for fat.”
The researchers also identified specific neurons that transmit to the brain the stimuli produced by fat when it reaches the stomach, as well as another group of neurons that informs the brain of the presence of sugars. In a study carried out by Mengton Li, of the Howard Hughes Medical Institute, once signaling pathways in mice were identified, scientists were able to block them with a drug, thus mitigating the desire for fat.
Zuker, who explains that his work consists of “understanding the fundamental biological mechanisms behind our preferences,” believes that this knowledge can be useful in combating an epidemic of diabetes and obesity, which is a huge health problem in today’s world.
“If you understand the circuit, perhaps you can begin to alter it with molecules that control its activity,” he points out, acknowledging that his team has already been in contact with the food industry to propose alternatives that satisfy the demand for fat in the intestine without causing negative side effects.
“There are two groups of people who can benefit from these interventions. One is made up of those who have clinical problems: in their case, it would be possible to intervene with a compound that allows [the brain and the gut] to begin to dissociate,” Zuker notes. “The second group is made up of general consumers. With them, the logic would work as in artificial sweeteners, the difference being that not only should the tongue be satisfied, but also the intestine-brain circuit.”
“Conceptually, maybe there is a way in which we can maintain the attraction to sugar or fat, but without the excess calories.”