Research has just identified a new specialized neural circuit between the gut and brain that promotes the consumption of high-fat foods.
Sugars and fats are essential nutrients for life and for this reason evolution has provided animals with systems that detect the presence of these substances in food.
The food industry very aggressively exploits this innate propensity for sugar and fat by producing processed products that contain high levels of these two nutrients, at levels far in excess of those normally found in nature.
The excessive stimulation of the brain caused by repeated exposure to these industrial products therefore promotes the overconsumption of sugar and fat (and therefore calories) and the development of obesity. In addition, all countries without exception that have incorporated these industrial products into their diets have seen rapid spikes in the incidence of obesity and obesity-related diseases.
Attraction is independent of taste
So far we have attributed the attraction of fat mainly to its organoleptic properties, i.e. the pleasure caused by the presence of fatty foods (ice cream, chocolate, butter) in the language.
However, research recently published in the prestigious journal Nature suggests that the nervous system also plays a key role in the desire for fatty foods1.
The researchers found, unsurprisingly, that within a few days, mice exposed to water bottles containing different substances quickly developed a strong preference for the one containing fat.
However, and this is the most interesting aspect of the study, this attraction does not appear to depend on the detection of fats in the tongue: genetically engineered mice, in which the fat receptors are located on the tongue, respond in the same way to the presence of fat.
In other words, even if they didn’t taste the fat, the animals were still able to detect its presence and developed a strong attraction to the solution containing the fat.
The gut-brain axis
This phenomenon seems to be caused by the presence of a detection system that informs the brain about the presence of fat in the digestive system: after a high-fat meal, the blood vessels that perfuse the intestines send a signal (via the vagus nerve) that activates a group of neurons , which are located in the taste nucleus, a region of the medulla oblongata (rachidial bulb) specialized in the interpretation of sensory stimuli.
Figure Adobe Stock
The vagus nerve
This pathway of communication seems absolutely necessary to explain attraction to fat, because genetic manipulations that prevent these neurons from responding to the signal from the gut eliminate attraction to fat entirely.
In other words, our innate attraction to high-fat foods isn’t just a matter of taste. Rather, it is an evolutionarily chosen adaptation whose purpose is to encourage repeated fat consumption to maximize energy intake.
This gut-brain connection has certainly played a key role in the survival of the human species, especially in times of food shortages. On the other hand, the many fat-laden industrial products offered to us in our era of food abundance literally hold this system hostage, resulting in excess calorie intake that promotes the onset of obesity and excess fat-related diseases.
1. Li M et al. Gut-brain circuitry for fat preference. Naturereleased September 7, 2022.