**2. Mechanisms present in obesity**

The number of adipocytes increases in the early age but reaches a maximum in youth and remains constant regardless of weight changes. In overweight or moderate obesity, the cells grow by the accumulation of lipids, without increasing their number. However, when obesity increases to more severe levels, the number of adipocytes will always increase [3].

Adipose tissue can be made up of large adipocytes (hypertrophy) or many small ones (hyperplasia). These two mechanisms contribute to the expansion of adipose tissue. In adults, hypertrophy is the mechanism that predominates and has been detected, which is strongly related to diet, while hyperplasia depends on genetics [4].

When there is an imbalance between the amount of energy consumed and that used by the body, it begins to store the excess energy in the form of triglycerides inside the adipocytes. These adipocytes begin to become hypertrophic, which causes free fatty acids to be released into the circulation (lipotoxicity), as well as the adipocytes changing their immunological balance which promotes the production of proinflammatory cytokines [5].

Obesity is a chronic state of low-grade inflammation. During the development of obesity, macrophages infiltrate the visceral white adipose tissue, causing chronic inflammation of low intensity that is characterized by the upregulation of proinflammatory adipokines such as TNFα, and decrease the concentration of antiinflammatory adipokines such as adiponectin. In addition, saturated fatty acids and TNFα, derived from adipocytes and macrophages, result in a cycle that leads to chronic inflammation of fat cells [6], as shown in **Figure 2**.

Also, during obesity, adipose tissue produces a greater amount of reactive oxygen species (ROS) which causes oxidative stress. This stress in turn leads to the abnormal production of adipokines (chronic low-grade inflammation), where it has been shown, for example, that the concentration of adiponectin is inversely related to the concentration of ROS [7].

#### **2.1 Abdominal obesity**

The white adipose tissue is metabolically active itself that participates in the metabolic regulation and physiological processes such as the inflammatory response, vascular function, and the secretion of hormones and adipocytokines [8].
