One of the reasons why obesity should be classified as a chronic multifactorial disease is due to the complex multifactorial etiology that causes a chronic progressive disease. For decades, there has been widespread discussion as to whether obesity is caused by dietary behavior or by the obesogenic environment that reduces individuals' physical activity levels. However, these factors work together with biological, metabolic, genetic, and psychological factors that lead to the complexity of obesity. Obesity develops over time through an imbalance between energy consumption and energy expenditure, therefore excess energy is deposited in fat cells causing weight gain. Attributing the cause of obesity to an imbalance in the energy system resulting from overeating and lack of physical activity is too simplistic and does not recognize that obesity is caused by large multifactorial factors, which lead to the development of a chronic disease. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Firstly, environmental agents cause an imbalance of the energy system including an increase in food intake which is increased due to the obesogenic environment which is the modern environment whereby the consumption of high content foods is encouraged energy with a high sugar and fat content (Chaput et al., 2011). Additionally, chemicals such as phthalates and bisphenol are often found in the environment and are associated with obesity because they disrupt metabolism. This points to environmental factors associated with obesity. There are numerous behavioral agents that cause obesity by affecting the system of energy imbalance influencing increased eating behaviors, such as emotional eating where individuals use food in response to their emotions (Fischer et al., 2007) , prescription of antidepressants such as mirtazapine (Chandra et al., 2018) and antipsychotics such as clozapine, smoking cessation and low physical activity. For example, low participation in physical activity increases sedentary behavior which imbalances the energy system by reducing energy expended. Psychological factors are largely comorbid with weight gain, with large associations between depression and obesity (Blaine, 2008) with broad links to eating behaviors such as depression increasing emotional eating and calorie intake. There are large metabolic factors that unbalance the energy system through disordered signals of hunger, satiety, and fullness, which are not fully understood. For example, a number of peripheral peptides have been shown in research to induce satiety signals in the brain, examples of these peptides are leptin, cholecystokinin (CCK), glucagon-like peptide-1, and peptide YY (PYY). which, when disordered, increase food intake (Geliebter, Ochner & Aviram-Friedman, 2008). More importantly, leptin binds to receptors in the brain that control food intake, some may be genetically predisposed to leptin deficiency, which alters the energy balance system. Some individuals have leptin dysregulation or a leptin receptor mutation, abnormalities in the proopiomelanocortin (POMC) gene or the melanocortin-4 receptor system. Various genes have been identified that contribute to obesity, for example genetic variants of fat mass and the obesity-associated gene (FTO) predispose to changes in BMI and body weight that lead to obesity (Frayling et al., 2007) . Furthermore, genome-wide studies have discovered 58 genes that contribute to obesity, which identifies the role of genes involved in predisposition.