Food intake (eating) is a form of behavior that is subject to conscious control. In practice, many obese and weight-gaining individuals claim that their eating is out of (their) control. Mechanistic models describe the interplay of biological and environmental forces that control food intake. However, because human food intake is characterized by individuals intervening to adjust their own patterns of behavior, food intake should reflect interactions among biology, environment, and attempted self-imposed control of behavior. In general, humans display a system of weight regulation that is asymmetrical--a reduction in body weight is strongly defended but weight gain is not. The body seems to tolerate a positive energy balance. There is no mechanism that can detect a positive energy balance per se or that can implement a sufficiently strong correction to behavior to maintain body weight in an environment that promotes consumption. The evolutionary process has favored biological traits associated with preferences for high energy density (sweet and/or fatty) energy-yielding foods. The control of food intake in obese or weight-gaining individuals may display various risk factors that favor an increase in energy. These include the preference for high energy-dense over low energy-dense foods, weak postprandial inhibitory signaling, strong hunger traits associated with low leptin levels after weight loss, and the consumption of fatty foods. In addition, many individuals (up to 47% of some samples) display binge eating patterns, whereas approximately 16% show either night eating or nocturnal eating. Because energy expenditure is only loosely coupled to energy intake, sedentariness does not down-regulate food intake.