1 · Sugar, fat and salt, all high at once
Mechanism 1 is the pleasure combination (hyperpalatable): many ultra-processed recipes push sugar, fat and salt high at once, which makes it easier to keep eating.· In natural foods, sugar, fat and salt are rarely all high at once: fruit is mostly sugar, meat mostly fat and a little salt· Many ultra-processed recipes do exactly that, pushing several of these high at the same time and tuning them repeatedly against consumer taste scores
The brain side:
· Food reward does raise dopamine in the nucleus accumbens (NAc), but far less than cocaine does (Hernandez & Hoebel 1988, microdialysis in rats). The problem with ultra-processed food is not that it is stronger than drugs, but that this weak stimulus arrives every day
· Volkow 2008 review: obesity and addiction overlap in dopamine circuits, and striatal D2 receptor availability is lower in obesity (the same direction as drug addiction, to a lesser degree)
· Food addiction is a hypothesis: Gearhardt 2009 built the Yale Food Addiction Scale (YFAS) to identify addiction-like eating; the symptoms were most strongly tied to ultra-processed foods high in refined carbohydrate and fat
Compared with whole foods: an apple or a bowl of plain rice tastes relatively simple, and after a certain amount the brain's enough signal comes more easily; foods with several of these high at once make it easier to keep eating.