Juices can be used to extend your fasting period. If you normally break your fast around noon, you can use a juice at that time to ease your hunger and give you an energy boost, so you can fast for a couple more hours. That juice won't activate the digestive system because the fiber has been removed. This one is a bit controversial.
Some people allow lemon water when fasting, however, fasting means consuming zero calories. A cup of water with half the juice of a lemon has 6 calories. Juices should not be drunk during fasting, as they are high in sugar and therefore contain calories. In general, it's best to avoid alcohol altogether during fasting, as it contains calories that will interrupt the fast.
Alcohol can also dehydrate the body and increase blood sugar levels as soon as it reaches the bloodstream. When choosing a beverage during your fasting period, consider calories. Drinks with calories greater than a single digit can interrupt your fast and undo your effort. Even some low-calorie beverages, such as diet soda, flavored waters, or anything containing artificial sweeteners, can cause an insulin response and interfere with fasting.