Eating is a necessity, but it is also a pleasure and it is precisely unhealthy foods rich in fats and sugars that are most appealing to us, a mystery that has not yet been solved. Now, a new study carried out by researchers at the Monell Chemical Senses Center (USA) scientific institute may help explain this preference. Its authors analyzed internal neural wiring, revealing separate pathways for fat and sugar cravings, as well as a worrying finding: excessive combination of these pathways triggers our desire to eat more than usual.
The taste of food influences our choices, but it is not clear which precise circuits in our brain are involved in the decision. The vagus nerve sends internal sensory information from the gut to the brain about the nutritional value of food, but the molecular basis of reward in the brain associated with what we eat is not fully understood.
“Food is the definitive reinforcement of nature,” said Guillaume de Lartigue, lead author of the study. “But it has been a puzzle why fats and sugars are particularly attractive. We have now identified that nerve cells in the gut, rather than taste cells in the mouth, are a key factor. “We found that fats and sugars recruit different gut-brain pathways, which explains why that donut can be so irresistible.”
Ultimately, this research provides insight into the factors that control “motivated” eating behavior, suggesting that a subconscious internal desire to consume a high-fat, high-sugar diet has the potential to counteract dieting efforts. The results have been published in Cell Metabolism.
Combining fats and sugars increases the release of dopamine
The researchers used advanced technology to directly manipulate fat or sugar neurons in the vagus nervous system and showed that both types of neurons trigger a release of dopamine in the brain’s reward center in mice. They discovered two pathways in the vagus nerve dedicated to this: one for fats and another for sugars. These circuits, which originate in the intestine, transmit information to the brain about what we have eaten, setting the stage for food cravings.
To determine how fats and sugars affect the brain, they stimulated the intestinal vagus nerves with light. This, in turn, induced the mice to actively seek out stimuli, in this case food, that activate these circuits. The results indicated that sugar and fat are detected by discrete neurons in the vagus nerve and activate parallel but distinct reward circuits to control the reinforcement of specific nutrients.
“We discovered that fats and sugars recruit different gut-brain pathways, which explains why that donut can be so irresistible.”
Not only that, but they also discovered that the simultaneous activation of fat and sugar circuits creates a powerful synergy. “It’s like a double whammy to the brain’s reward system,” de Lartigue said. “Even if the total calories consumed in sugar and fat remain the same, the combination of fat and sugar leads to a significantly greater release of dopamine and, ultimately, overeating in the mice.”
This finding helps explain why dieting can become a challenge. Human brains may be subtly programmed to seek out combinations high in fat and sugar, regardless of conscious efforts to resist. “The communication between our gut and our brain occurs below the level of consciousness,” Lartigue explained, adding: “It is possible that we crave these types of foods without even realizing it.”
In the team’s opinion, this line of research can contribute to the future development of strategies and treatments against obesity. Targeting and regulating gut-brain reward circuits could be a novel approach to avoiding unhealthy eating habits. “Understanding the wiring diagram of our innate motivation to consume fats and sugars is the first step in rewiring it,” says Lartigue. “This research opens up exciting possibilities for personalized interventions that could help people make healthier choices, even when faced with tempting treats,” she concludes.
