The markedly high prevalence of obesity contributes to the increased incidence of chronic diseases, such as diabetes, hypertension, sleep apnea, and heart disease. Because of high prevalence of obesity in almost all countries, it has been the focus of many researches throughout the world during the recent decades. Along with increasing researches, new concepts and controversies have been emerged. The existing controversies on the topic are so deep that some researches argue on absolutely philosophical questions such as “Is obesity a disease?” or “Is it correct to treat obesity?” These questions are based on a few theories and real data that explain obesity as a biological adaptation and also the final results of weight loss programs. Many people attempt to lose weight by diet therapy, physical activity and lifestyle modifications. Importantly, weight loss strategies in the long term are ineffective and may have unintended consequences including decreasing energy expenditure, complicated appetite control, eating disorders, reducing self-esteem, increasing the plasma and tissue levels of persistent organic pollutants that promote metabolic complications, and consequently, higher risk of repeated cycles of weight loss and weight regain. In this review, major paradoxes and controversies on obesity including classic obesity paradox, pre-obesity fat-but-fit theory, and healthy obesity are explained. In addition, the relevant strategies like “Health at Every Size” that emphasize on promotion of global health behaviors rather than weight loss programs are explained.