A specific hunger for carbohydrate-rich foods has been observed in animals and human beings and appears to be regulated by the brain neurotransmitter serotonin. Consumption of a carbohydrate-rich meal increases the synthesis and release of brain serotonin (by enhancing the brain uptake of its precursor, tryptophan). As a consequence of this increased release of serotonin, carbohydrate intake is decreased at the next meal. Consumption of protein does not increase brain serotonin levels or decrease carbohydrate intake. A subgroup of obese individuals who consume carbohydrate-rich snack foods at specific times of day or evening has been identified. Such individuals do not routinely snack on protein-rich foods, and their consumption of calories and nutrients at meals is not excessive. Evidence is presented that carbohydrate snacking seems to be related to a "need" to increase the level of brain serotonin; treatment with a drug, d-1 fenfluramine, that increases serotoninergic neurotransmission significantly decreases carbohydrate snack consumption. Weight loss among the population of carbohydrate cravers might be most successful if treatment includes either a diet or drugs that increase brain serotonin activity when the need to snack on carbohydrate is most likely to occur.