What are the cons of juice fasting?

Juice fasting, also known as juice cleansing, has become a popular diet trend in recent years. It involves consuming nothing but fruit and vegetable juices for a set period of time, typically ranging from 1-7 days. Proponents claim that juice fasts can help detoxify the body, stimulate weight loss, and provide a host of other health benefits. However, there are also some potential downsides to be aware of.

Nutritional adequacy

One of the main concerns with juice fasts is whether they provide adequate nutrition, especially over longer durations. While fruit and vegetable juices do contain important vitamins, minerals, and antioxidants, they lack protein, fat, and fiber. Going without solid food for days at a time can therefore lead to nutritional deficiencies.

According to the USDA, the recommended daily intake for adults is:

Nutrient Recommended Intake
Protein 46 grams (women), 56 grams (men)
Fiber 25 grams (women), 38 grams (men)

Juice fasts provide very little, if any, protein and fiber. Even a 3-day juice fast may be low in important nutrients like calcium, iron, vitamin B12, and zinc.

Blood sugar spikes

Since juices are high in natural sugars and lack fiber, they can cause big spikes in blood sugar levels. Rapid rises in blood sugar put stress on the body and can be dangerous for diabetics or prediabetics.

The fiber in whole fruits and vegetables helps slow the absorption of sugars into the bloodstream. Juicing removes this beneficial fiber, meaning the sugars enter the blood rapidly.

Studies show that fruit juices have a very high glycemic index, comparable to soda and other sugar-sweetened beverages.

Increased hunger

Juice fasts involve severe calorie restriction, since juices contain far fewer calories than solid meals. This significant decrease in calorie intake can leave many people feeling hungry, lethargic, and unsatisfied.

Solid foods increase satiety and fullness more than liquids. The lack of protein, fat, and fiber in juices also contributes to feelings of hunger during a juice fast.

Potential for disordered eating

For those predisposed to eating disorders or with a history of disordered eating, juice fasts can be dangerous. Calorie deprivation for several days may trigger binge eating and other harmful patterns once normal eating is resumed.

Those with diabetes, low blood pressure, kidney disease, liver disease, chronic fatigue, nutrient deficiencies, or who are underweight should avoid extended juice fasts and consult a doctor first.

Difficulty sticking to it

Drastically reducing food intake for several days is difficult for most people to sustain. Hunger, fatigue, irritability, and headache are common complaints, especially in the initial few days of a juice fast.

Many people find it challenging to stick to a juice fast for more than 2-3 days. Going back to normal eating after an extended fast can also be problematic.

Not a long-term solution

The weight loss achieved on juice fasts is often temporary. These diets are restrictive and unsustainable long-term, making weight regain likely.

Once normal eating is resumed, the lost weight usually returns quickly if no permanent dietary changes are made. Juice fasts alone don’t teach skills for long-term healthy eating and weight management.


Pre-made juices from shops and delivery services don’t come cheap, especially if used for multiple meals daily. Expect to spend $10-15 per day at a minimum if relying on bottled juices.

Making fresh juices at home requires an investment in a juicer ($100-200) and large quantities of fresh produce. Either way, juice fasts are a pricey proposition.


Juice fasts require a lot of planning, shopping, prepping, and cleaning. Juicing enough fruits and veggies for multiple days is time-consuming and generates a lot of dishes.

Portioning juices into separate containers and constantly drinking them throughout the day interferes with normal work and activity schedules. Maintaining a juice fast while traveling or away from home is also very inconvenient.

Potential food waste

Since it takes several pounds of produce to produce a pint of juice, juicing generates a high volume of leftover pulp and fiber. Some of the nutrients remain trapped in the insoluble fiber, which is discarded.

Unless the leftover pulp is used for other recipes like smoothies or muffins, it essentially goes to waste. This contradicts the goal of many juice fasters to follow a more eco-friendly, sustainable diet.

Lacks research

Despite celebrity testimonials and anecdotal reports, there is limited scientific evidence that juice fasts are beneficial or even safe long-term.

Very few robust studies have looked at the effects of juice fasts lasting more than a couple of days. More research is needed on the potential risks and side effects, especially with extended duration fasts.

Not suitable for everyone

While juice fasts are generally not advisable, they may be downright harmful for certain populations:

  • Children and adolescents
  • Pregnant or breastfeeding women
  • Those with diabetes or blood sugar issues
  • Anyone with an eating disorder or disordered tendencies
  • People who are underweight or malnourished
  • Individuals with kidney problems or gout
  • Those with chronic health conditions like heart disease, cancer, liver disease, etc.

Anyone considering a juice fast, especially of 3 days or longer, should consult their doctor first.

Possible side effects

Some potential side effects and complications of prolonged juice fasts include:

  • Fatigue and low energy
  • Headaches
  • Dizziness or lightheadedness
  • Nausea
  • Constipation
  • Diarrhea
  • Food cravings
  • Irritability and mood swings
  • Trouble concentrating
  • Disordered eating patterns
  • Gallstones
  • Low blood pressure
  • Kidney problems
  • Deficiencies of protein, iron, calcium, vitamin B12, etc.


In general, extended juice fasts of more than 2-3 days cannot be recommended due to potential nutrient deficiencies and health risks. Most people would be better off eating their fruits and veggies rather than juicing them.

That said, brief 1-3 day juice fasts are likely safe for most healthy adults. They can be used strategically before special events or as an occasional “reboot.” However, juice fasts are a quick fix rather than a sustainable eating pattern for the long haul.

People who truly want to improve their health should focus on eating more whole fruits, vegetables, lean proteins, fiber-rich carbs, and healthy fats. Lifestyle changes like regular exercise, adequate sleep, stress management, and mindful eating will better support weight loss and wellbeing over the long term.

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