**1. Introduction**

To date, it is estimated that more than a billion adults are overweight and over 300 million adults are classified as obese worldwide [1]. Owing to the dramatic prevalence of obesity, there is a drastic increase in obesity-associated diseases, including hypertension, type 2 diabetes, dyslipidemia, kidney disease, heart disease, cancer, obstructive sleep apnea, and osteoarthritis. The adipose tissue, also called fat, includes white adipose tissue (WAT) and brown adipose tissue. Obesity is mainly caused by an excessive accumulation of fat mass in WAT to the extent that health may be adversely affected. WAT functions as both a metabolic and an endocrine organ that lies at the heart of a complex network participating in the regulation of various biological responses, including inflammation, immunity, endocrine, and metabolism [2].

Adipose tissue is a dynamic tissue, and the mass of adipose is generally determined by a balance of adipocyte proliferation, differentiation, enlargement, and lipolysis. Increased adipose

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

mass may result from the enhancement of adipocyte formation (adipocyte differentiation, also called adipogenesis), enlargement of adipocyte (lipogenesis), and/or reduction of lipolysis that contribute to fat accumulation in WAT. Adipocyte differentiation is defined as the formation of new adipocytes from multipotent stem cells or preadipocyte precursors [3]. In brief, adipogenesis is divided into four steps, including initial growth arrest, mitotic clonal expansion (MCE), early differentiation, and terminal differentiation-development of mature adipocyte phenotype [4]. White and brown adipocyte differentiation share common pathways and possess specific characteristics. Unless specified, "adipocyte differentiation or adipogenesis" indicates white adipocyte differentiation here.
