I think people should give digestive systems more credit for being able to handle very bad diets! I mean, c'mon! In famine/civil-war torn countries, people live off just a handful of rice a day, for years! They really do! Some may die in the process and there are rampant vitamin deficiency diseases, but death is not inevitable, it is just more likely as the quality of your diet diminishes and you become more susceptible to ailments.
Between the ages of ~8 and 12 I ate nothing but Nutella spread sandwiches for lunch, then baked beans and sausages, with milk, for evening meal. (Oddly, after 4 years, one lunch time the Nutella sandwiches made me feel sick, and I have never eaten one since! That might indicate something about the limits of mono-diets!)
While I was at University I lived off nothing but potato chips, chocolate biscuits and 4 to 6 pints of milk a day for 4 years! (And just a very occasional beer. :shy:) I find eating food is just a boring, time consuming necessity and do not seem to derive the same sort of pleasure other people do. I am not unique in having odd mono-dietary preferences. I read of someone who is allergic to essentially everything except Spam, and has eaten nothing else since childhood! (I cannot vouch for the accuracy of the story, but I have no reason to doubt it.)
Whereas others seem to accept it as part of their way of life; I am lead to believe some Asian religious orders serve up a form of starchy gruel for their monks as part of their 'pure' life, and that's their lot!
Our need for food is an organic one, from which the body then constructs the substances it needs. Is the definition of 'Vitamins & essential minerals' not simply those things our body needs that it cannot produce for itself from carbohydrates and proteins? I thought this is exacly what it meant?
Edit wrt post #13; But I do agree that vitamins taken 'unnaturally' are unlikely to pass into the system in the same way.