A dieter on a juice fast eats only uncooked vegetables and drinks just water and fresh fruit juices for a period of one to three days. Ideally, only organic fruits and vegetables are consumed. In addition, the water should be at room temperature. A juice fasting is usually undertaken during spring, when the weather is warm.

Although a juice fast can provide vitamins and antioxidants to the body, it also comes with adverse side-effects. Minor effects such as bad odor, headaches, fatigue, constipation and hypoglycemia usually follow a juice fast. However, dangerous effects such as decreased heart rate, low blood pressure, kidney complications, diarrhea and rapid weight loss may also occur. Anyone undertaking a juice fast should resume their normal eating habits if such symptoms arise.

In addition, certain people must avoid juice fasting. They include: diabetics, people with liver and/or kidney complications, anemic people, people with low blood pressure, underweight people, people with any type of cancer, people undertaking surgery, people on medication, pregnant women and children.

Some precautions should be taken during a juice fasting. For example, fasters should not drink juices of grapefruits or pomegranates. Also, animal fat, sugar, caffeine, alcohol and cigarettes should be avoided for at least a week before the fast.