Andrew Reitemeyer, Facebook asked:
I have read that the digestive system monitors food for the presence of certain nutrients and will encourage the brain to desire food until the need is met. Is this consensus science and if so which nutrients are involved?
Susie - There is certainly some evidence if you induce a state of significant deficit that animals will show preferences for foods that contain those, but in terms of in a relatively healthy population, whether we actually show specific cravings for nutrients, that's a much tougher question to find evidence for.
As a psychologist, I'm very interested in food cravings because they quite often point to foods that are desirable because we’re meant to limit them, because they're tempting, and because we’re trying to restrict them when we’re dieting. So, chocolate for example is a very commonly craved food and it’s not about any kind of nutrient deficiency, and this is really nicely demonstrated by a data from Paul Rozon who gave people who crave chocolate a box and he said, “Whatever is in the box, have this when you're craving chocolate.” The box was either empty or it had capsules containing cocoa powder or white chocolate or milk chocolate. White chocolate remember has no sort of cocoa. It has just cocoa butter. It doesn’t have any bioactive ingredients. And what they found was that cravings could be reduced in chocolate cravers by white chocolate and by milk chocolate. So it wasn’t that the cravings were really directed towards any kind of nutrient or any kind of physiological deficit, but rather because of the comfort of eating something that was really delicious – melt in the mouth, sugar and fat, absolutely delicious. That's where cravings come from.
I would think that desires for sweetness and calories would actually be of evolutionary benefit, even though it may no longer be as much of a benefit.