Learn English – How to describe a person who loves everything about nature and the outdoors

Cryophilic is the only word that comes to my mind:

Having an affinity for or thriving at low temperatures.

The antonym is thermophilic.

A health nut springs immediately to mind. One definition reads: "a person who eats health foods and does exercises to become healthy." But it is an idiomatic expression and one which non-native speakers may be unfamiliar with.

Health-conscious is perhaps more suitable for your needs. But the type of person you are describing sounds to me pretty obsessed. Related but not exactly pertinent, a recently discovered eating disorder called, Orthorexia nervosa, means someone who will not ingest any food considered unhealthy.