Alternatively, the consumption of chocolate may be a homeostatic mechanism for regulation of behavior of some neurotransmitters involved in regulating appetite, hunger, mood, and addictive behavior. Several studies have found that negative moods are especially important between cravers and have an upward trend "emotional eating". Low levels of serotonin in the CNS have been associated with depression, addiction, and obsessive-compulsive disorder, and ingestion of carbohydrates, especially chocolate, was alleged to selectively increase the absorption of tryptophan and production of serotonin by the brain.
Several animal studies have shown that drugs that increase levels of serotonin on postsynaptic receptors cause a reduction in carbohydrate intake.
However, studies have also shown that ingestion of even a small amount of protein with carbohydrates denied any neurochemical effect. A typical chocolate bar contains about 10% protein by weight, a quantity that may be sufficient to block an increase in the level of serum tryptophan and leading to increased levels of serotonin in the CNS. Moreover, according to this hypothesis, all carbohydrates with high glycemic index should be equally effective in promoting the synthesis of serotonin and elevate mood and should be the recipients of the desire for food.