woman pouring juice

Juice cleanses have become the poster child for trendy diets that promise big results. According to Medical News Today, there are many different juice cleanse protocols. Some involve drinking only juice, while others may combine the juice with certain supplements or "cleansing" procedures like enemas. Common juice ingredients include dark leafy greens, lemon, apple, cucumber, beets, and ginger. Proponents of juice cleansing say it encourages rapid weight loss, rids the body of toxins, and helps reset and revitalize the digestive tract.

Green juice is a particularly popular option. In a survey of 2,200 Americans conducted by YouGov, a quarter of people admitted to being a bit freaked out by the look of green juice, but most of them still believed that it’s a healthy beverage choice and an excellent way to consume more fruits and vegetables (via Men’s Journal). In fact, more than 20 percent of those surveyed said they’d rather get veggies like beets and dark leafy greens in juice form.

It’s no surprise, then, that juicing has become big business. According to Forbes, the fresh-pressed juice industry grew to more than $3.4 billion by 2016. But what really happens when you drink your fruits and veggies instead of eating them whole, especially when that’s the only thing you’re consuming? Here’s a look.

Your body won’t be magically purged of "toxins" when you start a juice cleanse

Many people embark on a juice cleanse hoping it will rid their body of harmful toxins. But according to registered dietitian Keri Glassman, they aren’t a miracle product with special detoxifying properties. In an interview with Shape, she explained, "A multiple-day, juice-only detox diet doesn’t seem necessary for our bodies, which naturally detox through the liver, kidney, and GI tract." The expert continued, saying, "There’s no scientific evidence to suggest that our bodies need help getting rid of waste products, and I wouldn’t recommend a cleanse in place of a normal diet."

There are a few ways you can aid your body in its natural process, however. According to Healthline, you may want to consider upping your water intake, reducing the amount of alcohol you drink (alcohol is a toxin, after all), elimiating excess sugar and processed foods, getting adequate sleep, and more.

A juice cleanse will make it easy to consume the recommended number of fruits and vegetables

woman juicing fruits and vegetables

The U.S. Department of Agriculture (USDA) recommends that adult women between the ages of 19 and 50 eat 2.5 cups of vegetables a day, while men in the same age range should eat 3 cups. Women over 50 need only 2 cups, while men over 50 should aim for 2.5 cups. When it comes to fruit, specifically, the USDA recommends women age 19 to 30 eat 2 cups daily, while women 31 and older need only 1.5 cups. Adult mean of all ages should aim for 2 cups of fruit a day.

While that may not sound like a lot, most Americans don’t meet these recommendations. According to research conducted by the Centers for Disease Control and Prevention (CDC), only 12.2 percent of American adults eat the daily recommended amount of fruit, and a measly 9.3 percent eat the recommended amount of vegetables (via Time).

The USDA noted that a cup (8 ounces) of 100 percent fruit or vegetable juice counts as a serving, however, so it’s easy to see how someone could quickly meet (and exceed) their daily recommendations while doing a juice cleanse.

You may not be able to absorb all the micronutrients in your juice

man drinking green juice

Even in juice form, fruits and veggies are packed with important vitamins, minerals, and other micronutrients. But if you’re only drinking juice, your body won’t be able to make use of many of them.

According to Medical News Today, fat-soluble vitamins (A, D, E, and K) need to be consumed with a source of fat in order to be absorbed. They perform many vital roles in the body, including assisting with vision (vitamin A), boosting the immune system (vitamins A, D, and E), helping with calcium absorption and bone growth (vitamins D and K), and preventing blood clots (vitamin E). Unfortunately, no vegetables and very few fruits contain significant quantities of fat.

Fat is also needed to absorb carotenoids, plant substances with antioxidant properties. In a 2004 study published in the American Journal of Clinical Nutrition, researchers fed participants an all-vegetable salad with either fat-free, reduced-fat, or full-fat dressing and then measured the blood concentration of three carotenoids: beta-carotene, alpha-carotene, and lycopene. The researchers found that no carotenoids were absorbed by participants who ate the fat-free dressing, and those who ate the full-fat dressing absorbed more carotenoids than those who ate the reduced-fat version.

You may lose weight on a juice cleanse, but only temporarily

woman measuring waist in mirror

Many people embark on a juice cleanse hoping to shed some unwanted pounds, and that’s exactly what happens — but only in the short term. It comes down to math. Based on the energy balance model of weight control, you’ll lose weight if you consume fewer calories than you burn (via WebMD).

Most juice cleanses are very low in calories — usually just 800 to 1,200. This is well below the guidelines set by the 2015–2020 Dietary Guidelines for Americans, which recommends, depending on age, between 1,600 and 2,000 calories for sedentary women and between 2,000 and 2,600 for sedentary men and more for active individuals.

But according to Men’s Health, the weight loss that comes with a juice cleanse is just a short-lived illusion. Most of the weight lost isn’t fat but water weight, and possibly even muscle. And once you go back to your regular diet (or, really, any diet that includes solid food), a lot of that weight will come back. You may even gain weight, since depriving yourself while on a juice cleanse may cause you to overeat later. For long-term weight loss, experts suggest sticking to a less extreme and more balanced healthy eating pattern (via Men’s Health).

Your body won’t get the fiber it needs from a juice cleanse

hand pulling on roll of toilet paper

While drinking your fruits and vegetables may be more convenient than eating them, the juicing process leaves out an important part of these foods: fiber. As registered dietitian Trista Best told Health Digest, "Having to discard the bulk of the solid, fibrous portions of fruit and vegetables for juicing means you are throwing out fiber. Fiber is primarily found in these portions that are not being consumed when you opt to juice."

According to the Mayo Clinic, adult women should aim to get 21 to 25 grams of fiber a day, depending on age, while men should shoot for 30 to 38 grams. Fiber provides many benefits, including helping to regulate bowel movements, improving digestive health, lowering cholesterol, and preventing blood sugar spikes.

If your trips to the bathroom are less than optimal while on a juice cleanse but you don’t want to give up entirely on the idea of juicing, you may want to consider at least swapping out your juicer for a blender. As Best pointed out, unlike juicing, blending retains all parts of the fruit and vegetable, including the fiber-containing skin and pulp.

You’ll be constantly hungry on a juice cleanse

bottle of juice surrounded by ingredients

According to the Cooper Institute, how satiated (aka full) you feel after eating depends on the macronutrient content of that meal. While food that takes up a lot of space in your stomach may cause immediate fullness, protein and fiber have the biggest role to play in controlling when you’ll be hungry again. Since juice cleanses rely on drinking a lot of liquids, they’ll fill your stomach up quickly, but the fiber that’s lost during the juicing process means you’ll be ravenous again in no time. And most fruits and vegetables are low in protein, with the exceptions of dried fruits, beans, legumes, and corn — and it’s pretty unlikely your juice cleanse includes any of these.

Gulping down rather than chewing your meals may also contribute to feelings of hunger. As Harvard Health Blog explained, chewing thoroughly slows down eating and allows your brain time to receive hormonal signals from your digestive system that food has been consumed and it’s now time to stop eating and digest. Hormones involved in this process include cholecystokinin (CCK) and leptin. Leptin may also interact with the brain chemical dopamine to produce feelings of pleasure after eating.

Your gut bacteria may change on a juice cleanse

woman pouring green juice

Going on a juice cleanse for even just a few days may be enough to alter your gut microbiome. According to Healthline, the gut microbiome is a collection of trillions of microorganisms — mostly bacteria — that reside throughout your digestive tract and are most concentrated in a part of your large intestine called the cecum. This microbiome is made up of hundreds of species of microorganisms, and which species are present depends in large part on your diet.

The microbiome serves many beneficial functions, including helping to digest certain nutrients, producing vitamin K and certain B vitamins, and protecting us against other microorganisms that can cause disease (via University of Washington). Everyone’s gut microbiome is unique, but for optimal health it’s important that this collection of microorganisms be large and diverse.

In a study published in Scientific Reports in 2017, a research team investigated how a three-day diet of vegetable and fruit juices changed the microbiomes of participants. They found that Firmicutes and Proteobacteria bacteria significantly decreased, while Bacteroidetes and Cyanobacteria increased. The researchers pointed out that the bacteria that had increased in number were those most associated with weight loss.

Your heart health may get a boost from a juice cleanse

woman holding green juice

According to the Centers for Disease Control and Prevention, heart disease is the leading cause of death in the United States, taking the lives of approximately 655,000 people each year. While there are many factors that can contribute to heart disease, juicing may actually provide some protection for your ticker.

A 2017 paper published in the International Journal of Molecular Sciences concluded that "drinking juices might be a potential way to improve cardiovascular health, especially mixtures of juices because they contain a variety of polyphenols, vitamins, and minerals from different fruits and vegetables." Of course, you’d get these same benefits by simply adding juices to your regular diet, rather than going on a juice cleanse.

Nitrate-rich fruits and vegetables in your juice may be doing the heavy lifting when it comes to promoting heart health. Unlike the synthetic nitrates used in cured meats, the natural nitrates found in some fruits and vegetables appear to be beneficial for health. Common juice ingredients high in these natural nitrates include dark leafy greens, beets, celery, apple, banana, oranges, and strawberries. Research suggests that natural nitrates lower blood pressure, a major risk factor for heart disease (via CardioSmart).

Your juice cleanse could be damaging your metabolism

glass of beet juice surrounded by beets

The Master Cleanse and other juice diets promise quick weight loss, but they may actually be doing long-term harm to your metabolism, making it harder to control your weight in the future. This is because most cleanses provide few calories — often just 800 to 1,200. This can send your body into what’s popularly known as "starvation mode." According to Healthline, "What people generally refer to as ‘starvation mode’ (and sometimes ‘metabolic damage’) is your body’s natural response to long-term calorie restriction." The technical term for this response is "adaptive thermogenesis." When you consistently don’t meet your calorie needs, your body slows your metabolism as a protective measure to try to maintain your current weight.

A 2013 study published in the International Journal of Obesity found that this slowed metabolism that results from eating too few calories can last long after calorie restriction ends, and it may be a contributing factor to post-diet weight gain. Although one short juice cleanse likely won’t do irreparable damage, longer or repeated juice cleansing in an attempt to lose weight may wreck your metabolism.

You may get kidney stones on a juice cleanse

woman touching kidney area in pain

Although fruit and vegetable juices may boast a high concentration of micronutrients, the juicing process also results in a high concentration of the anti-nutrient oxalic acid. According to the National Kidney Foundation, oxalic acid (also known as oxalate) binds to calcium in the digestive tract to create a salt. While these salts usually leave the body through stool and urine, in some individuals they collect in the kidneys and become painful kidney stones. These stones are much more common than you might think. Roughly 7 percent of women and 13 percent of men will get kidney stones at least once in their lives, and having one kidney stone puts you at much higher risk for additional stones.

Even more alarming, a paper published in 2018 in the American Journal of Kidney Diseases discussed the case of a woman who suffered end-stage kidney failure after consuming excessive amounts of oxalate while following a juice cleanse. Although the woman had normal kidney function before beginning the cleanse, it’s important to note that she also had several predisposing factors. Oxalate-heavy fruits and veggies likely to be in your juice cleanse include dark leafy vegetables like spinach and kale, beets, berries, oranges, and cranberries.

A juice cleanse may increase your risk for type 2 diabetes

fruit and vegetable juices with accompanying produce

Although many people consider juice a healthy beverage, that reputation isn’t necessarily deserved. Some commercially bottled juices, for instance, may contain added sugar to make them more appealing. Even 100 percent pure fruit juice can be loaded with sugar. According to NPR, apple juice contains 65.8 grams of fructose (a simple sugar) per liter, while cranberry juice has 55.4 and orange juice has 28.3. For comparison, Coke has 62.5 and 7-Up has 45.8.

The large amounts of sugar you’re likely consuming during a juice cleanse can put you at greater risk for type 2 diabetes, both directly and indirectly. According to Healthline, fructose can damage the liver, which in turn can lead to insulin resistance, a condition in which the body doesn’t respond normally to insulin. Over time, this can lead to type 2 diabetes.

Large amounts of fructose can also lead to weight gain and more belly fat, both of which are risk factors for diabetes. So, if you’re going to do a juice cleanse, focus on getting plenty of vegetable juice and sticking to lower-sugar fruit juices such as tomato, watermelon, and grapefruit.

You may experience energy crashes and brain fog when starting a juice cleanse

exhausted man at computer

You may start a juice cleanse hoping it’ll energize you, but you’re more likely to end up feeling both physically and mentally sluggish, thanks to many juices’ high sugar content (via Healthline). Sugar provides a quick jolt of energy, but it can leave you feeling exhausted just as fast. If all you’re consuming is juice, you’re likely to have many such sugar crashes.

The Sanford Medical Center explained that these crashes occur when our bodies are flooded with tons of sugar and the pancreas must respond by pumping out lots of insulin. This sudden spike and subsequent drop in blood glucose levels leaves us feeling tired, irritable, and shaky. Fiber and protein can help slow sugar’s absorption, but unfortunately juice cleanses don’t provide much, if any, of these.

Your mental abilities may also suffer because of the sugar in juice. According to Patient, "Brain fog is a general term for a set of symptoms affecting the cognitive processes." Brain fog can affect memory, information processing, concentration, higher-level thought, and speaking to or understanding others. Healthline noted that both high and low blood glucose levels can cause brain fog.

You’ll lose muscle on a juice cleanse

man at gym with bottle of juice

In an interview with Harvard Health Blog, registered dietitian and nutritional science professor Nancy Rodriguez explained that protein is essential for growing and maintaining muscle. It’s also needed to make hair, blood, connective tissue, antibodies, and enzymes. The recommended dietary allowance (RDA) for protein is expressed as a formula: 0.8 grams per kilogram of body weight. Rodriguez and other health professionals, however, suggest that getting up to twice the RDA is a "safe and good range to aim for."

Although the fruits and vegetables in your juice cleanse may be packed with micronutrients, one thing they unfortunately don’t have is protein. Very few fruits and vegetables contain significant amounts of protein (unless you’re planning to get creative and start putting dried fruit, beans, or corn in your juice). When you’re drinking nothing but juice, you’re starving your muscles (and the rest of your body) of the protein it needs. To make matters worse, Men’s Health pointed out that juice cleanses are so low in calories that you likely won’t have the energy to work out, which will cause additional muscle loss.

You could end up with food poisoning from a juice cleanse

woman grimacing in pain

When it comes to juices, you have two options: pasteurized or fresh squeezed/cold pressed. There are pros and cons to each. According to Healthline, many commercially bottled juices are pasteurized in order to both kill potentially harmful bacteria and extend the juice’s shelf life. But, in an interview with Shape magazine, registered dietitian Keri Glassman explained that the high temperatures used in pasteurization can destroy "live enzymes, minerals, and other beneficial nutrients."

On the other hand, the Food and Drug Administration (FDA) warned, "When fruits and vegetables are fresh-squeezed or used raw, bacteria from the produce can end up in your juice." Children, older adults, pregnant women, and individuals with a weakened immune system are most at risk from foodborne pathogens.

Foodborne illness, aka food poisoning, usually appears one to three days after drinking the contaminated juice. The FDA recommended avoiding purchasing unpasteurized juice and, if juicing at home, to thoroughly wash the produce and your hands and cut away any bruised or damaged parts of fresh fruits and vegetables. You can also cook produce before juicing, though this may change the taste and add extra time in the kitchen.