When rats eat lots of sugary, fatty food for a long time, their brain's pleasure center becomes more active with dopamine, which might make them keep eating even when they don't need to.

When rats are stressed and eat sugary food, their brain’s chemical balance changes differently when they’re hungry versus when they eat again—especially in the area linked to pleasure and reward.

When you eat tasty food, your brain releases dopamine right away from the taste, and then again later from your body sensing the nutrients—two different brain areas handle each part.

Whether a rat is hungry or just ate, and what it’s been eating before, changes the levels of two key brain chemicals in its reward center.