There is a medical term that implies you are not supposed to eat or drink for about 12 hours before a surgery, and that is 'NPO' or 'Nil Per Os.'
That is not a term that implies you should only be on IV nutrition, however.
This may depend on the motivation behind the lack of eating. Lack of hunger is anorexia. Fear of gaining weight is anorexia nervosa. A lack of eating is aphagia.
Abstinent is a medical term sometimes used for a patient who is not drinking alcohol.
That would be NPO.
abstinence from alcohol
Adipsia.
Anacusis is the medical term meaning complete deafness.
Syncope is the medical term meaning fainting.
Polydipsia (medical) means excessive or abnormal thirst.
Lamina is the medical term meaning layers.
Sensation is the medical term meaning feeling.
Flexion is the medical term meaning bending
Atrophy is the medical term meaning shrinking.
Alimentation is the medical term meaning food.
Eructation is the medical term meaning burping.eructation
Asphyxia is the medical term meaning suffocation.Asphyxiationasphyxiation
Acornuate is the medical term meaning hornless.
Unguis is the medical term meaning nail.