The World Health Organization describes obesity as “a chronic complex disease defined by excessive fat deposits that can impair health,” declaring obesity as a major health concern and disease in 1997. In 2013, the American Medical Association recognized the obesity disease condition as one associated with various pathophysiological problems requiring intervention. The global obese population continues to increase, calculated to be greater than 1 billion in 2024, or about 1 in every 8 persons. Likewise, the prevalence of obesity among Korean adults continues to increase. As a significant health risk factor and one of the main causes of chronic disease, obesity is caused by the increased intake of ultra-processed food, excessive nutritional intake, inadequate physical activity, smoking, heavy drinking, sleep disorders, particular chemicals and drugs, environmental toxins, endocrine disruptors, stress and mental illness, genetic and congenital disorders, et cetera. Obesity has detrimental effects on physical, mental, psychological, and sociological well-being, leading to body dysmorphia and image disfiguration, discomfort, disability, disease, and death. Obesity is not simply a risk factor for chronic diseases, rather, it is an epidemic of a complex chronic illness that is difficult to be cured. Obesity is exacerbated in the modern era due to rapidly changing societal lifestyles and its associated multifaceted effects. Due to the difficulty in the management of obesity, the individual causes and societal influence on lifestyle must be tightly controlled. The most decisive pathological process of obesity is inflammatory changes of adipose tissue. Produced by adipose tissue, various hormones and inflammatory agents affect normal tissue to induce an inflammatory response, leading to insulin resistance and a disruption of neuroendocrine homeostasis, particularly the reduction in thyroid hormone and the imbalance of adrenal hormones. In this article, the author will review the functional medicine aspect of altered metabolic adaptation in obesity.