In layman's language, this drug-nutrient interaction can be defined as the food you are taking that may be affecting the medicine you are prescribed to take, and vice versa.
Surprisingly, this is something some medical practitioners overlook when it is as vital as them diagnosing the patient and giving the appropriate therapy or treatment may it be with surgery, with an equipment or medication. Lucky you if the physician outrightly gives you instruction as to what to eat or not to eat in contrast to the medicine he is giving.; or when he informs you that you need to fo to a dietitian for further instructions for the nutrient interaction affecting drug absorption, effectiveness or metabolism.
Be informed that there are certain food and patterns of dietary consumption affecting your medical treatment. Maybe at times you are told that this medicine should be taken on a full stomach because it is highly acidic and may cause you discomfort. But how often have you heard that this medicine should be taken on a full stomach because the medicine will not be absorbed on an acidic environment? Or that this drug can be further absorbed if taken without fat since it is lipid soluble? If nutrients in food affects drugs, drugs as well affects these nutrients. Example of which is an antihypertensive agent, melthyldopa, which prohibits absorption of iron, vitamin B12 and Folacin. The list goes on, and the best thing one can do is to ask the physician or the dietitian what possible contraindications of drug with nutrients (or vice versa) affecting hwat was given you and of what appropriate measures to take into consideration.
Last but definitely not the least, AVOID self-medication.