Compared to calorie-free foods, foods with calories in them hit the human brain with big effects, even if people don’t appear to consciously like the flavors all that much.

There appear to be two unrelated brain circuits that kick into gear when people consume things, Dana Small, a Yale University psychologist who studies people’s responses to food and one of the scientists who performed this study, tells Popular Science. There’s one that’s related to consciously liking flavors. And then there’s another that responds to glucose in the blood, which is an indicator of that person’s metabolism of food. “The thing the brain really cares about are the calories,” Small says.

Small’s study comes after a few years of research into mice, rats and fruit flies have found that the animals are able to sense nutrition independently of taste. …

Over time, animals learn to prefer mixtures containing real sugar instead of artificial sweetener.