A food addiction is a behavioral addiction that is characterized by the compulsive over-consumption of high fat or sugary foods – the two types which markedly activate the reward system in humans and other animals – despite adverse consequences. Sugar and high fat food have both been shown to increase the expression of ΔFosB, an addiction biomarker, in the D1-type medium spiny neurons of the nucleus accumbens; however, there is very little research on the synaptic plasticity from compulsive food consumption, a phenomenon which is known to be caused by ΔFosB overexpression. Psychological dependence has also been observed with the occurrence of withdrawal symptoms when consumption of these foods stops by replacement with low fat or sugar food. Professionals address this disorder by means of behavior therapy.