If you are eating a lot of whole grains, fresh fruits and veggies, you might notice that you have to poop more often (which is a good thing) but you may have to plan that into your daily activities.
You are also likely to undertake a new experience with tastes and sensations. Fast food is primarily fat, salt and sugar. Whole foods tend not to have these things, but what they do have is a multitude of “new” taste sensations ranging from tart, to slightly bitter, to umami to clean, to spicy to bland. Like with giving up cigarettes, I think you will learn to embrace (or hate) the fact that you can taste/smell/feel all of the new things that you will be eating.
Don’t expect a healthy diet to look or taste anything like fast food, it just doesn’t. If you are lucky, like I was when I became a vegetarian, a whole new culinary world will open up for you. If you are un-lucky, and not really a willing participant, then you will be disgusted and disappointed by the multitudes of wonderful, healthy food that is available to you.
Know that is often takes 10 tries at eating a “new” food before it becomes palatable or agreeable with regards to taste. Try not to give up, if at first something tastes “yucky” or has a “weird” texture, you might have to try different preparations of the same item (say tofu or mushrooms) before you find a preparation that you like.
Good luck, and Bon Appetite!