Is Juice Fasting Dangerous?

Juice fasting often involves using a juicer to extract the liquids from fresh fruits and vegetables and drinking them right away. This approach is healthier than using commercial fruit juices, which are usually loaded with sugar --- or salt in the case of vegetable juices --- and preservatives. A juice fast is primarily done for two reasons: enhanced detoxification and weight loss. However, in some cases, it can be dangerous.

Nutrient Deficiencies

Juices are rich in nutrients, such as vitamins and minerals, so you get some of what you need to stay healthy if you're fasting. But juices are not rich in other nutrients, such as bone-building calcium --- unless they're fortified --- or in inflammation-fighting essential fatty acids. As such, you should not do a juice fast for longer than three days, according to Brenda Watson, a certified nutrition consultant and author of "The Detox Strategy."

Effect on Blood Glucose

A juice fast significantly increases your intake of sugar. Both fruit and vegetable juices contain natural sugars, but fruit juice has a higher sugar content. In recommended amounts, sugars in fruit are not a problem. However, excessive consumption boosts blood glucose and insulin levels, which can be particularly dangerous if you're diabetic or pre-diabetic. Also, you have to use several fruits and vegetables when juicing to make one glass, which increases the sugar content.

Fungal Infections

The high sugar content in fruits provides a hospitable environment for fungal organisms that you may already have in your body, such as candida, thereby causing them to multiply, warns Watson. Symptoms of candida overgrowth include allergies, digestive problems and fatigue.

Precautions

Juice fasting --- and other types of fasts --- can cause side effects such as headaches, dizziness and lethargy. Consult your doctor or a nutritionist if you plan to do a juice fast for longer than three days, especially if you are pregnant or have diabetes or any other medical condition. At the end of a juice fast, re-introduce food gradually. Start with lighter foods first, such as green leafy vegetables and citrus fruits, recommends Watson. The following day, add small amounts of whole-grain carbohydrates and wait an additional day or two before adding meat, fish or dairy.