system
Given the following post, respond as if you're commenting on Reddit:
human
Whitebread. Where did those nutrients go?

refined foods always are said to be less nutritious. Where did they go? what is involved in the refinement process of foods that removes the good part.
gpt
One class of nutrients that are particularly sensitive to processing are the ones we would consider anti-oxidants.  That includes Vitamins A, C, D, E, and K, as well as other micronutrients.  Using your example,during processing of wheat into Wonderbread flour, it undergoes processes of dehulling, grinding, bleaching, and drying.

Each of these processes has a way of destroying some of the nutrients contained within.  A lot of the fat soluble vitamins in wheat are contained in the bran, a slightly oily coating on the wheat berry.  Dehulling and polishing removes this layer.  What vitamins remain are in the "white" part of the wheat, which is then ground up and bleached, so that nobody is mislead that they might be eating whole wheat bread.  These two processes expose the inner parts of the wheat to air, which can oxidize the nutrients inside.  Depending on what bleaching process is used, even more can be destroyed (sunlight+air decimates vitamin C, peroxides can do the same to just about everything).  Washing and drying (if necessary) completes the process.  If the flour is washed with water at some point before use, it can leech out the water-soluble vitamins like Vitamin C, the B-group Vitamins.

To counteract all this, manufacturers usually add the missing vitamins back at the end, but they can only add in what is known to be missing.  If it's some lesser-known nutrient that went away, it'll stay gone.