The process of adding nutrients lost during food processing or cooking is called nutrient fortification or nutrient enrichment.

Here's a breakdown of the terms:

* Nutrient fortification: This is a broad term referring to adding any type of nutrient to a food product, whether it was originally present or not.

* Nutrient enrichment: This term specifically refers to adding back nutrients that were lost during processing or cooking.

For example, adding iron to breakfast cereals is considered nutrient fortification, while adding back thiamin and niacin to white bread after milling is considered nutrient enrichment.