For the record, dopamine is a neurotransmitter, which means it is a signal sent from one brain cell to another in order to convey information. After eating, dopamine is released in our brain as a reward, it’s our body’s way of thanking us for engaging in a survival enhancing activity. The problem is, when you eat more, more dopamine is released. Therefore, the body responds by decreasing sensitivity to dopamine, mainly through down-regulating the production of receptors. This dulls the effect of dopamine, making us want to eat more sugar and fat, to experience the same pleasure inducing effect that our body previously perceived with less sugar and fat. This is probably the reason why rats fed diets high in fat and sugar, will continue to consume foods high in fat and sugar, despite the electric shocks researchers use to try to deter them.
I learned about this fact from: Gearhardt et al. Can food be addictive? Public healthy and policy implications. Addiction, 106, 1208-1212.