This is – well, I won’t say impossible – but there is no good reason to believe that it’s true, and lots of reasons to discount it as a reasonable hypothesis.
There are many well-documented examples of animals that are capable of adjusting their diet to self-medicate. Ingested a toxin? Eat a bunch of clay to act as a physical binder and chemical chelating agent to absorb the toxin. Infected with a parasite? Start eating this bitter leaf you never eat because it contains high concentrations of a secondary metabolite that will kill the parasite. It’s not clear how much of this is physiologically-driven ‘instinct’, and how much is individually-learned or culturally-transmitted behaviour (e.g. gram bonobo taught ma bonobo taught baby bonobo). However, this behaviour is always in response to the presence of a toxin or infection, dealing with an acute medical condition rather than a chronic dietary one – it’s a response to a pharmacological need, not a nutritional one.
Obviously, humans and all other organisms are capable of responding physiologically to nutritional deficiencies. In the broadest sense, that’s just called being hungry. When it comes to wide categories of marconutrient (carbs proteins fats), you might get cravings for a particular category, particularly if you’re regularly very active. Again, some of this is perhaps physiological and ‘instinctive’, but a lot of it is simply learned behaviour: you figured out before you were three years old that sugary things gave you energy, so if you’re low energy you know you should find something sweet.
But roomwithaview is suggesting something very different from these scenarios. They are suggesting that Mister44 felt a sudden craving to consume a material they had never before seen – and did not even regard as food – in an unconscious but direct physiological response to a micronutrient deficiency.
e.g.
a) Mister44 is running low on zinc
b) Mister44’s body / brain are unconsciously aware that they need more zinc
c) Mister44’s body/ brain becomes unconsciously aware that the plant root contains zinc
d) Mister44’s body/ brain compels them to eat the plant root
There is no compelling evidence that the human body is capable of parts b) and d). There is no reason to believe that your body can tell your brain, consciously or otherwise, that it is lacking in specific micronutrients, or to compel cravings for specific foods that will satisfy those deficiencies. People suffering from vitamin A deficiency don’t naturally crave carrots, sweet potato, and papaya. Even with pregnancy cravings, the classic case that everyone “knows” is true, probably isn’t true. I’m not aware of any good evidence that cravings for specific foods during pregnancy correlate with genuine nutritional needs; it’s far more plausibly explained by hormonal swings and changes in taste perception.
There is no plausible mechanism for part c). Your eye isn’t an atomic absorption spectrometer. Vitamins and minerals are non-volatile, so you can’t smell them. You cannot feel the presence of specific molecules with your skin, because your skin lacks the molecular-scale receptor proteins in your nose and tongue. There is no possible way for your body to detect the presence of 40 parts per million zinc in a plant root. So even if Mister44 were suffering from a specific mineral or vitamin deficiency, there is no mechanism by which their body could realize that it would be in the plant.
(Beyond the obvious inference, that is. Plants are living things that always contain some amount of iron and zinc and copper and quinones and ascorbic acid, because all animals and plants need all those things. If Mister44 is suffering from a specific micronutrient deficiency and they have a functioning instinctive micronutrient detector, it should be pinging at any of two dozen foods in the produce section far more loudly than at a random plant root they have never seen before.)
tl;dr While macronutrient-driven hungers and self-medication in response to a medical condition are both well established in both animals and humans, the proposed scenario is very different in both kind and degree from these phenomena. I’m not aware of any compelling evidence that micronutrient-deficiency-induced craving occurs in humans, and there is no plausible mechanism by which it could operate as suggested.
