Gary Wenk blurs the two:
For example, potatoes, tomatoes, and eggplants contain solanine and ?-chaconine, substances that can enhance the action of acetylcholine, a chemical in your brain that is vital to memory formation. Your mood might be enhanced slightly by eating fava beans because they contain L-DOPA, a precursor to the production of dopamine, the reward chemical in your brain. Whether these food-borne compounds actually affect your brain depends upon how much you consume and your own personal physiology. This might explain why some people find it quite rewarding to eat potatoes or eggplants.
Morphine-like chemicals capable of acting upon the brain are produced in your intestines when you consume milk, eggs, cheese, spinach, mushrooms, pumpkin, and various fish and grains. Dairy products in particular contain a protein known as casein, which enzymes in your intestines can convert into beta-casomorphin. In newborns, that beta-casomorphin can easily pass out of the immature gut and into the developing brain to produce euphoria.