Hi Scarlett.
I really do hate to buck the trend here but fasting is not all bad news. There are definitely some benefits for the body. However, if you have never fasted before, I would not suggest that you do go from nothing to 3 weeks. Your body is likely to be able to cope for up to 40 days without food (that doesn't mean that you should do it - I'm just letting you know). You will feel weak after a few days and you will smell but this is the detoxification processes and they are not permanent. Please do not take my word for it - I'm not a doctor. I just want to bring a little balance here. By the same token, you don't have to take the word of the person who told you to fast but I would say try fasting for a day, then another time for 2 days then 3 days. NEVER stop drinking water. Very risky and of course, always check with your doctor. All the best.