One of the substances produced by the fat cells in our body is called leptin. If we have more fat cells, we are able to produce more leptin, and this plays a key role in regulating energy intake and expenditure, including appetite, hunger, metabolism and behavior. When leptin levels are high, animals act as if they are adequately nourished, they eat less, become more active, and increase the activity of their immune system. In contrast, leptin levels are low; animals will eat more and rest more because they need to conserve energy which allows them to put energy into their immune system. However, animals with the obese gene do not produce leptin, which means they feel hungry, try to eat as much as possible, and try to conserve energy by not moving much. Do animals really stop eating when they have high leptin levels and start getting hungry when they have low leptin levels? For the online search result, I found an article published by M. Flavia Barbano and Martine Cador who are studying at the Victor Segalen University of Bordeaux in France. Also, this report was carried out at the Neuropsychology Laboratory of the Victor Segalen University of Bordeaux. This paper used thirty-two rats and three experiments investigating the motivational, anticipation and consumption aspects of food. He tested the appetite of a rat that was satiated by feeding it its favorite food. The results are able to determine the authenticity of the Leptin theory using short and long term diet regulation. In the test, the investigators used about a month, which included moving the rats from a cage into the glass bowl, to obtain the result, and the research was successfully carried out...... middle of paper ..... .to eat chocolate cereal instead of normal food. However, the result of the second test was not the main point that verifies the authenticity of the leptin theory. In the third test, the investigator provided the normal food to the rats and fed them until they were full, which means the leptin level. are high in rats and the message sent from the brain will allow the rats to stop eating and start becoming active. At that point, the rats stop eating; the authors provided the chocolate cereals which are the preferred food of the rats in front of them when they contain a high level of leptin. Although the rat still ate some of the chocolate cereal, after a few bites the rats couldn't continue. The rats' desire for food clearly decreased due to the lower leptin level. Even when they are presented with leptin, it still plays an important role in their appetite..