Most metals consumed (albeit in only tiny amounts for select elements) will be directly converted to ions by the HCl in our stomach.
Then, as the question includes the word 'nutritional', commonly cited elements (in their ionic form) of particular import include: potassium/sodium (regulates fluid balance, muscle contractions, and nerve signals), iron (linked to hemoglobin and the transportation of oxygen in the blood), calcium/magnesium (maintains strong bones), iodine (required for creation of thyroid hormones and regulating the body's metabolism), chromium (important in the breakdown of fats and carbohydrates) and copper (instrumental in formation of red blood cells, maintenance of nerve cells and the immune system), to mention a few.
Of the mentioned elements, those having a caloric impact include chromium and iodine.
Note, elemental carbon, especially in the form of charcoal pills or activated carbon, should be avoided (not nutritional or even caloric), see discussion here.
Further, I would argue, that as the human body generates a chemical-based electric current (see this discussion), it is probably not wise to introduce a very good cathode (namely carbon). Unwanted solvated electrons and radicals created therefrom, most likely do not promote good health, and in ones' body, may supply an electrode to promote electrochemical (or battery) cell activity.