The smell of food makes you feel full

Bad news for the manufacturers of the weight loss pills Zepbound and Wegovy, which brought Elli Lilly and Novo Nordisk combined sales of US$12.9bn in 2024? Scientists at the Max Planck Institute for Metabolism Research have discovered a new network of nerve cells in rodent models that evokes a feeling of satiety when smelling food in normal-weight mice, but not in obese mice – a new therapeutic approach?

The researchers used brain scans to investigate which regions of the mice’s brains respond to food odours, and were able to identify a new group of nerve cells in the medial septum of the brain. These nerve cells respond to food in two steps: When the mouse smells food, the nerve cells fire and create a sensation of fullness. This happens within a few seconds because the nerve cells are directly connected to the olfactory bulb. The nerve cells react to different food smells, but not to other smells. When the mice started to eat, the nerve cells were inhibited. Overall, the mice ate less when these nerve cells are active before eating.

In obese mice, the same group of nerve cells was not activated when the mice could smell food. The mice did not feel fuller and did not eat less overall. The authors point out that it is already known that obesity disrupts the olfactory system, including neuronal activity in the olfactory bulb. The newly identified group of nerve cells could also be affected by obesity.

“Since we discovered that the pathway only reduces appetite in lean mice, but not in obese mice, our study opens up a new way to help prevent overeating in obesity”, says Sophie Steculorum, who led the research. 

The human brain contains the same group of nerve cells as the mouse. However researchers have just to prove that the process is the same as in mice. Reactivation of the olfactory system in obese people might then be a way