Obesity has become an epidemic in industrialized and developing countries. In 30 years, unless serious changes are made, a majority of adults and many children will be classified as overweight or obese. Whereas fatness alone endangers physiological performance of even simple tasks, the associated co-morbidity of obesity including metabolic syndrome in all its manifestations is a far more critical problem. If the current trend continues as predicted, health care systems may be incapable of handling the myriad of obesity-related diseases. The financial costs, including those due to medical procedures, absenteeism from work, and reduced economic productivity, will jeopardize the financial well-being of industries. The current review summarizes the potential contributions of three processes that may be contributing to humans becoming progressively more overweight: circadian or chronodisruption, sleep deficiency, and melatonin suppression. Based on the information provided in this survey, life-style factors (independent of the availability of abundant calorie-rich foods) may aggravate weight gain. Both epidemiological and experimental data support associations between disrupted physiological rhythms, a reduction in adequate sleep, and light-at-night-induced suppression of an essential endogenously produced molecule, melatonin. The implication is that if these problems were corrected with life-style changes, body-weight could possibly be more easily controlled.