Adjustment Time

I’m wondering how much time it takes for a body to adjust to a new nutrition plan. I’ve heard that chemicals, like those in processed foods, can take a while to completely leave your body. So, I’m thinking it could be weeks or even a month of eating whole foods before I start to feel different (more energy, less digestive issues, etc.) and see a difference (weight loss). Is there an average time that most people start feeling and looking better?