grammar
δεν είναι μόνο ... αλλά και ...
This correlative pattern adds a second, equally important aspect and is useful when you want to broaden a claim without repeating yourself. In the story, it expresses that health has more than one dimension: not only physical, but also mental. You can reuse it in sentences such as «Η δουλειά δεν είναι μόνο απαιτητική αλλά και δημιουργική.» and in English: “Work is not only demanding but also creative.” It is especially natural in formal or reflective prose.
Η δουλειά δεν είναι μόνο απαιτητική αλλά και δημιουργική.
Work is not only demanding but also creative.