This is the 18083rd most frequent Polish word.
żywieniu
"Żywieniu" means "nutrition" or "feeding" in English.
The word 'żywieniu' here refers to nutrition and is used in the prepositional case to indicate the topic of the dietitian's discussion.
Dietetyk mówił o zdrowym żywieniu.
The dietitian talked about healthy nutrition.
In this context, 'żywieniu' is used to denote the role of plants in the nutritional process, again in the prepositional case.
Książka skupia się na roślinach w żywieniu człowieka.
The book focuses on plants in human nutrition.
'Żywienia' is used in a context explaining an approach or methodology, showing its function as the root word related to dietary practices.