A major conceptual revision for understanding the physiology and behavior of eating has expanded the dual-center theory of hypothalamic facilitatory and inhibitory centers for eating. The sensitive hypothalamic eating centers are part of a broad complex of neuroregulator interactions that includes a peripheral satiety system (gastrointestinal and pancreatic hormones released by food passing through the gastrointestinal tract) and a broad neural network affecting feeding, within the brain. Eating behavior is now known to reflect an interaction between an organism's physiological state and environmental conditions. Salient physiological variables include the balance of various neuropeptides and neurotransmitters, metabolic state, metabolic rate, condition of the gastrointestinal tract, amount of storage tissue, and sensory receptors for taste and smell. Environmental conditions include features of the food such as taste, texture, novelty, accessibility, and nutritional composition as well as other external conditions such as ambient temperature, presence of other people, and stress (Blundell and Hill 1986).