One example mentioned above is the Daniel Fast which is a partial fast, that eliminates some common things from our daily diet. According to the Bible, approved foods on the Daniel Fast include vegetables, fruits, whole grains, legumes, nuts, and seeds, while meat, dairy, and all sweeteners are avoided. The fast is based on Daniel's experience and focuses on "plant-based meals" for a set period, with water as the primary beverage. .
If you have health conditions* that prohibit you from being a part of the Daniel Fast, there are other options. Choose something from your daily routine (i.e. specific/individual foods or beverages) and fast in from that for the next 21 days. Remember, the details are not as important as the spirit in which you participate.
*If you have any known medical conditions or suspect such conditions, consult your doctor before beginning any fast.