Fasting works for many people
Fasting has been used for healing, and other beneficial effects, for thousands of years. The tissues and organs of the body store small amounts of some toxins and they can build up to the point where they do affect your health.
There are many different approaches to fasting and detoxification of the body. There are even foods which may be eaten that have a cleansing effect, so that it is not necessary to completely go without food, in order to rid the body of toxins. For some people, especially the frail or elderly, it may not be wise to stop eating for a long time.
The subject of fasting and detoxing is rather extensive and cannot be covered in this one response. However, I can tell you that I have fasted several time in my life and have felt a positive difference in my health each time. Once I fasted for 10 days and lost several pounds. I did take fluids and most of them were fresh squeezed juices such as wheat grass juice and carrot. I had periods of feeling VERY tired, followed by periods of feeling VERY energized. They say that the tired feeling comes as a result of your body releasing a lot stored toxins into your circulation. I fasted like this when I was in my 20's and 30's. I tried going without food for one day, now that I am in my 60's, and found it to be a much different story. I found that I became extremely weak and dizzy and felt I had to have some food. So, now I eat light soup and salads and lots of fresh juices when I feel the need to detoxify. It seems to work pretty well. Some supplements and other natural things that I have found helpful in detoxing are... pascalite clay (from Big Horn Mountains in Wyoming... Google it!), enemas, fresh sqeezed juices with fresh garlic gloves, fucoidan, kombucha (keeps my appetite down) and green things like spirulina, barley juice and seaweed and salads.