Appetite suppression effects have been found in two different types of brain cells, in two separate studies.
In the first study, a type of glial cell (cells that surround, support, and protect neurons) called tancytes have been found to have the same savory taste receptors that the tongue has. They sense the taste called umami, the taste of protein. That taste is what makes something taste meaty. It is activated by (among other things) monosodium glutamate (MSG), which is why MSG is put into food.
Glutamate (and its acid form, glutamic acid) is one of the essential amino acids that make up proteins. Two other essential amino acids, arginine, and lysine, are what the tancytes in the brain detect.
The tancytes sit in the brain where they are in contact with the cerebrospinal fluid, where they can sense the amino acids, and in contact with the part of the hypothalamus in the brain that controls energy levels and body weight. When they sense that the levels of arginine and lysine are high enough, the tancytes send appetite suppression signals to the hypothalamus that decrease appetite. The tancytes respond in as little as 30 seconds to lysine and arginine. Tancytes can also generate new neurons, allowing the hypothalamus to be retrained through diet.
Foods beside meat that contain useful levels of lysine and arginine are plums, apricots, avocados, almonds, and lentils. Eating these thus reduce hunger faster than other foods. High protein foods such as these also digest more slowly, so they don’t quickly raise blood sugar levels, thus reducing food cravings and keeping you satiated longer.
Tancytes also have the same sweet taste receptor that the tongue has. They detect glucose levels in the blood this way, possibly adding another appetite suppression signal.
The second study focused on neurons in a higher-level part of the brain, the medial septal complex, which is implicated in emotion and cognition. They found that these neurons contribute to appetite suppression by sending signals down to the hypothalamus.
By activating these neurons, the researchers were able to control appetite without causing the side effects other interventions cause, such as anxiety and changes in physical activity.
Together, these two studies provide two separate targets for potential diet drugs, but also for interventions based on diet.