Common Questions About Juice Cleanses

What to Know Before You Fast

Juicer with beets, oranges, and ginger
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Juice cleanses, sometimes called juice fasts, are popular among people who claim flooding their bodies with liquefied fruits, vegetables, and other raw foods for a short amount of time is an effective way to flush out toxins and boost overall health. But they aren't safe for everyone, nor have supplements promoted for enhancing cleansing or detoxifying been tested for safety. And there's little evidence to show that detoxing is healthy, necessary, or even really "works," according to Harvard Medical School. If you want to do a juice cleanse, you likely have questions about what it's like and how to go about it. Here are answers to some common concerns.

How Do You Know If It's Safe for You?

Start by checking with your doctor. Some common reasons for not doing a cleanse are if you're pregnant or nursing or you have diabetes or chronic liver, kidney, or gallbladder problems. The same goes if you take certain prescription medications, especially anticoagulants or antiplatelet medications: Juice cleanses or fasts can reduce the level of blood proteins and alter the way prescription drugs are metabolized in the body. You shouldn't fast if you have surgery coming up. And it's never safe for children to do a cleanse.

What Does It Feel Like?

You'll probably feel really hungry at first—uncomfortably hungry—and very tired. You could have some pretty severe headaches, especially if you're a heavy coffee or tea drinker and you suddenly cut out all caffeine. Going cold-turkey like that can lead to caffeine withdrawal symptoms—headaches, sleepiness, and trouble concentrating.

As the cleanse progresses you may have symptoms of detox, including body odor, bad breath, a coated tongue, constipation, loose stools or diarrhea, gas, runny nose or nasal congestion, or acne. None of these should be intolerable. If you have symptoms that are extreme, check with your doctor. Cleanses shouldn't be uncomfortable.

Could You Have Serious Side Effects?

You could, depending on how long you fast and what your general health is when you start. Side effects of juice cleanses include fainting, low blood pressure, headache, stomach pain, dehydration, low potassium levels, heart arrhythmias, vomiting, appendicitis, and kidney problems.

Note that including a lot of beet juice in your juice can give your stools a red tinge. That can be scary, because it may look like blood. But there are some serious causes of red stools, so if you have any doubt whatsoever, see your doctor.

Should You Be Concerned About Overdosing on Juiced Fruits or Vegetables? 

Given how important it is to include produce in the daily diet, you'd think a juice fast would be a golden opportunity to get lots of nutritious fruits and veggies into your body. And it is, but it's important to choose carefully. For example, raw cruciferous vegetables such as cabbage, broccoli, kale, watercress, radishes, and collard greens contain glucosinolates that may inhibit iodine intake and interfere with healthy thyroid function.

For some people, a substance called oxalic acid, found in spinach, Swiss chard, watercress, parsley, beets, nuts, and some berries, can be problematic if you have a kidney disorder or are prone to kidney stones. Oxalic acid can also be a problem if you have any of a number of other conditions, including gout, rheumatoid arthritis, and certain types of vulvodynia. It's not that you should avoid foods containing oxalic altogether, as they have lots of nutritional value, but it's not wise to consume them in large or concentrated amounts.

How Long Can You Stay on a Juice Cleanse?

A juice fast typically lasts for one to five days. Don't fast for more than three days without being monitored by a doctor, dietitian, or other nutrition specialist. Fasting for a prolonged time can lead to deficiencies of important nutrients, such as protein and calcium.

How Can You Prevent Constipation?

It's important to have regular bowel movements while on a juice fast because toxins are theoretically mobilized from the tissues and must be eliminated from the body, not just through stools but also urine and sweat. Otherwise, they may be reabsorbed in the body. Regardless of that, being constipated is unpleasant, so you may want to check with your doctor about safe ways to deal with it.

Can You Bring Your Juices to Work?

If it's stored tightly covered in the fridge, juice can be stored for 12 to 24 hours after juicing. If you're bringing it to work, pack it in a thermal container or nestled in an insulated lunch bag with ice packs. If your office has a fridge, transfer your juice as soon as you get to work.

Is It Okay to Exercise?

Yes, but keep it light; even moderate exercise can be too much. Walking is ideal. Most important, pay attention to how your body feels. If you're lightheaded or weak during a workout, stop and rest.

How Can You Stick to the Fast If You Have to Eat Out?

As much as you can, choose to eat the same foods in whole form that you're drinking as juice—raw salads, crudités, fresh fruit. And don't worry about eating if you have to. One or two solid meals during a juice cleanse won't ruin it.

When Can You Start to Eat Again?

After you finish a cleanse it's not a good idea to start eating lots of solid food right away. Take your time and break the fast slowly.

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