There is a lot of controversy over whether fasting is healthy or not. I believe the reason for that is that everyone is different, and you have to find out for yourself. For me, it seems extremely healthy. Whenever I have a disease like the flu or cold that doesn't seem to go away, I fast for two or three days and it goes away. So as soon as I feel I am coming down with a "bug", I go ahead and fast until it's gone, usually a couple days. But that's just me.
It can be very unhealthy for some people because the pesticides and poisons you speak of often store in the fat, so fasting can cause them to be released quickly. Also professional nutritionists and doctors often don't recommend it because it throws chemical balances off and causes havoc in some people.
One factor is in your "metabolic type". You can do tests to determine what that is, for instance I am a protein metabolic type. So I don't do well without protein, and whenever I eat vegetarian for very long I don't feel as strong.
I don't need a lot of meat, but a little.
Some people are fruitarians, which I believe is unhealthy because of too much sugar and not enough protein, but they think it is the best. It makes me very sick because I have low blood sugar.
So anybody that claims something is a cure-all shows they don't know what they are talking about.
Although fasting does often help clear toxicity, so does a good balanced, light diet with plenty of raw organic greens and lots of water, with whatever else your type requires for protein etc, combined with exercise. this clears toxins slower, so it's safer.
But I'm a believer that a 24 hour fast once a week is good for you too. I don't always do it, but if you start when you first get up, you have probably already completed more than eight hours. Start timing after dinner the night before, and 24 hours goes by quickly.