Junk food fiend is more like Fast food fiend. As long as the food isn't literal junk (aka bad or normal quality), there is no conflict between trait and lifestyle. I imagine Junk food fiend Foodies as prefering the restaurant version of street food: handmade, fresh sushi not from the freezer, pizza from homemade ingredients, perhaps cooked in the family circle, and hamburgers with premium meat.
The most adorable thing about junk food fiend sims is their ability to add sugar or bacon to any meal.