Fat taste as a primary taste is a new concept which can affect feeding behavior. Free fatty acids could activate the gustatory afferent pathway as another primary taste (sweet, salt, bitter, sour, umami). Our team demonstrates this activation by recording cerebral gustatory evoked potentials, in response to several solutions of free fatty acids. These new data could have a strong impact on the understanding of the physiopathology of obesity. In part, overeating in obesity is due to alteration of the homeostatic feedback created by the peripheral energetic status. Food is a key-point of the hedonic feeding behavior based to the reward system, which has consequences on calories consumption and sensory abilities. In this background, fat taste, altered in obesity for some authors, could be only the consequence of overweight. Fat taste could be modified by the feeding behavior and the body composition, because of alteration of the reward system involved into the acceptation of the palatable energy-rich foods such as lipids or carbohydrates. Alteration of the reward system should be taken into account in the physiopathology of obesity, and offers promising prospects about diagnosis and future treatment of obesity.