Just because something is "ancient" or has been used "historically" doesn't necessarily make it a good thing nor does it make it scientifically sound. Most of these sites seem to be personal sites, religious sites, or blogs. None seem to have scientific research and hard evidence; just a bunch of blanket statements. I do not see any articles on MayoClinic.com that support fasting. There may be signs that there is a connection between calorie restriction and longevity, but keep in mind that there is a difference between calorie restriction and fasting. Your Serendip link is apparently a student paper? He used WebMD as a reference, and here's an article that they posted about fasting (Fasting) that clearly states:
And all the sites tell you to consult your doctor before fasting. Have you done so? Whatever you decide is up to you, but I do think you should talk to your doctor before you jump into something like this.Some fasting diets claim that they can cleanse the body of impurities. However, there is no evidence that fasting detoxifies your body, or that your body even needs to be detoxified. It is naturally designed to remove toxins through the skin (by sweating), liver, colon, and kidneys.