Proper diet is important for your bones because proper diet keeps you healthy.

Nothing in particular. However in some contexts a proper diet can mean being for a specific type of person where sometimes able to juxtapose to a balanced diet in which these are a general, broader statement.

E.g. A proper diet for a swimmer is consists of more carbohydrates but a balanced diet is generally for anyone.

vegan

Proper diet helps keep you healthy and fit. Medicines are important if you fall sick or are injured.

because your bones will weaken and if your on a proper diet and drink milk then your bones will stay strong.