**4. Leptin as an energy balancer**

Leptin acts in the brain and maintains energy homeostasis through a negative feedback mechanism [29]. The process is mediated through the receptors in the hypothalamic area named the paraventricular nucleus, ventromedial hypothalamic nucleus, lateral hypothalamic area (LHA), and arcuate nucleus (ARC). The ARC is the primary site for leptin to integrate peripheral energy balance signals [30]. Recently, it has been observed that leptin could play a significant role in the long-term regulation of energy balance and short-term management of body weight and food intake. The gastric leptin produced because of the actions of the intestinal peptide serves as a local stimulus and plays a vital role in food digestion and absorption [31]. The particular area requires more investigations to prove the role of gastric leptin in food digestion and absorption. Research supported the predominant role of leptin in neuroendocrine mediated starvation through changing sympathetic nervous system activity [32].

Overweight or obesity is characterized by increased fat mass and is proportional to circulating leptin levels in individuals [33]. The elevated levels of leptin in body fluid are explained based on leptin resistance. The hypothesis was proved using rodents fed

*Biodiversity of the Adipocyte-Derived Hormone, Leptin DOI: http://dx.doi.org/10.5772/intechopen.100576*

with a high-fat diet and leptin sensitivity loss in ARC neurons [34]. At the cellular level, the inflammatory signals mediate the process of leptin resistance. The two significant characteristics of obesity connect with hyper-leptinemia and leptin resistance. At the molecular level, the leptin gene is over-expressed in overweight or obese individuals [35]. Apart from these functions, many researchers reported the genetic and epigenetic factors that control leptin action in energy homeostasis and food intake [36–38]. A better understanding of leptin-induced pathogenicity of obesity and obesity-related disorders and the regulation of energy homeostasis will provide an alternative solution in preventing obesity and obesity-related co-morbidities.
