Provided you take it step by step, fasting is the best way to get of anything that is foreign to the body. It will also rest the nervous system and revitalise all of the body's systems in general, including the immune system, so that recovery from such issues as the body's ability to expel toxins i the first place will be speeded up. Exactly why it's called a "fast", because it speeds up the healing process.
I have done many fasts, the longest so fat being a 19 day one. I only stopped short of my goal of conducing a 30 day fast because I live in the tropics and had contracted malaria.
I believe with the posted who stated that beneficial effects of fasting are cumulative. With each fast, you do feel better and better. At one point, I felt so good after fasting 3 times in a row, that I was elated.
I began fasting under supervision by numerous fasting experts. I recommend this if possible, but if not follow the advice of experts and beging with short (3 day) fasts, then gradually increase. Seven day fasts are a good happy medium for someone who wants optimum health without doing really lengthy fasts.
Note that, counter-intuitively, fasters will not in general feel all that hungry on a fast provided they drink adequate amounts of water.
An alternative to fasting to achieve many if not most of the benefits of fasting is to go on a very tightly controlled diet of fruit, vegetables, fruit and veggie juices and non meat or dairy protein sources (eg cashew nuts). I actually tested this on a glaucoma condition I had. I measured my reduction in IOP with both water only and the controlled diet I mentioned, and in both cases my IOP improved, showing that my nervous system was recovering. As soon as introduced heavier foods into the diet, such as meat and so on, my IOP rose again.
I noted similar benefits with toothaches. In several cases, I have avoided having my teeth pulled merely because I fasted on water for 3 days and the nerve underwent a full recovery.