There is a part of the code in TFC that determines whether an item is edible and adds something like food properties to it. This happens with any food from any mod, but it does not happen with food from GTFO, which is why if you eat any food from GTFO, the character's hunger value will not change.

This appears to mainly be an issue on the GTCEu side of things (note https://github.com/GregTechCEu/GregTech/blob/master/src/main/java/gregtech/api/items/metaitem/FoodUseManager.java, which uses a method which is removed in TFC's food stats).

Just to keep you informed, I have created a pull request in Gregification (GregTechCEu/Gregification#27), which is GTCEu's official compatibility mod that will be (eventually) released. This includes compatibility between GTCEu and GTFO food items with TFC. When this is merged, I'll close this issue.

Ok, Thanks!

Ok, I've gotten it merged, although you'll still have to wait to see when Gregification actually gets released.

Nice