Hey and welcome!
Full disclosure: I have never been totally addicted to fast food/processed food, or gotten most of my meals from these sources. I also am not strictly whole food- I eat whole foods 80-90% of the time.
However, I did used to eat much more if it than I do now. I live in a developing country, so fast food and processed food is hard to find. I HAVE to eat fresh, local ingredients because that's mostly all that is available
And you're right... I feel totally different when I eat a homemade vegetable soup made from carrots, leeks, potatoes, onions, and other goodies that were brought in from the farm this morning than prying open a can of thick, gloopy Campbells... or making fresh tomato sauce from real tomatoes and rosemary than buying a jar of Prego.
And I agree.. it is much easier to stay "on plan" and within calorie ranges when you're eating lots of legumes, beans, whole grains, veggies, and fruits than when you're eating Lean Cuisines. You get fuller faster and don't want to stuff your body with all those chemicals.
I think detox is a buzzword that the industry uses to sell products- the *general* opinion around knowledgable folks on 3FC is that it's a gimmick. The body does a pretty good job with detoxing itself.
I imagine what you mean is how long it takes to wean oneself off of craving junk food/high sugar products? I find it takes a couple of weeks. Not too long. And every day it gets a little easier
I do include sweets/desserts in my diet. I have no problem having a slice of apple pie I baked myself with apples and whole wheat crust, or a lemon bar made with sugar, not high fructose corn syrup. I find that these do not trigger an urge for junk food (though it certainly makes it difficult to not go back for a second piece, admittedly!)
What does trigger an urge for junk food, chips, candy, etc is eating some of it. Again, I do this from time-to-time on special occasions. If it's just a small portion every now and then, by the next day the urge for more is gone.
This is just my perspective... and I don't really know if I've helped answer any of your questions at all. I love whole foods lifestyles and wish you the best of luck on your journey