General synonyms:
* Nutritious
* Sustaining
* Wholesome
* Beneficial
* Healthy
* Strengthening
More specific synonyms:
* Invigorating (for something that gives energy)
* Restorative (for something that helps to heal or rebuild)
* Sustenance (for something that provides food or nourishment)
* Supportive (for something that helps maintain health or growth)
* Enriching (for something that adds value or benefit)
The best synonym for "nourishing" will depend on the specific situation and the type of nourishment being referred to.