Does the body really need juice cleanses to detox and “cleanse” the gut? Nutrition scientists have a clear answer: nobody needs a juice cleanse. And there are far better alternatives.
A reset for the body – that’s what juice cleanses promise. The detox is meant to rid the body of toxins, be gentle on the gut and give digestion a break.
Juice cleanses are popular and marketed as an effective way to detox and cleanse the gut. What sounds promising at first quickly turns out to be questionable – or simply unnecessary.
At a Glance
Juice cleanses are short-term, one-sided diets where only fruit and vegetable juices are consumed. The goals: detox, weight loss and a “reset” to kick-start a dietary change.
There’s no scientific evidence for the promised benefits of juice cleanses. There is evidence that juice cleanses often lack key nutrients: vitamins, minerals, fibre, protein and healthy fats.
The excessive sugar intake during a juice cleanse can negatively affect the gut microbiome. The extreme calorie deficit may lead to short-term weight loss – but also to unwanted muscle loss. There are far better options than a juice cleanse.
Thinking about a juice cleanse to shed a few kilos and detox? No wonder – the bold promises of rapid weight loss and detoxification can sound convincing.
Before you overhaul your diet so radically, it’s important to understand the physiology behind juice cleanses and what they actually do.
A juice cleanse usually lasts 3 to 7 days, during which you replace solid food with fruit and vegetable juices only. So instead of muesli for breakfast, you might have a vegetable juice and a fruit shot. At first glance, that doesn’t sound too bad.
People who choose a juice cleanse typically have two aims: detox the body and lose weight. These goals are pitched as a “starting signal” for changing eating habits – a so-called reset.
The underlying assumption is that the body needs a regular break to rid itself of toxins and chemicals. Drinking only fruit and vegetable juices is also said to be especially gentle on digestion and give it a well-earned rest. Supposedly, juices can at least “cleanse” the gut, if not actively detox it.
What sounds promising is, unfortunately, light on substance. There’s no scientific proof that such cleanses work. And fruit and vegetable juices lack important nutrients while delivering certain compounds – like free sugars – in excess.
A typical juice cleanse supplies 120 to 180 g of sugar per day. That’s 2–3 times higher than the maximum daily intake recommended by the German Diabetes Society and the German Nutrition Society. International bodies also recommend a maximum of 50 g of “free sugar” per day to help prevent the harms of high sugar intake.
“Free sugar” includes sugar added to foods, as well as sugars naturally present in honey, fruit-juice concentrates and fruit juices. Sugar from intact whole foods (e.g., an apple or an orange) doesn’t count towards this.
That means the sugar naturally present in fruit and vegetable juice does count as free sugar. Why? Because juicing removes key components of fruit and veg (e.g., fibre) that help modulate how sugar is metabolised and blunt the negative effects of free sugar. Without fibre in the diet, free sugars can cause blood glucose to spike rapidly – which, over time, can contribute to insulin resistance and even type 2 diabetes.
Over 7 days, a juice cleanse can load the body with as much sugar as expert groups suggest should be consumed at most over 25 days. That’s far too much for a so-called “detox” that’s supposed to be good for you.
The step that turns a fresh apple into apple juice is juicing. Stripped back to its core function, juicing separates the liquid from the solid parts of a food. In other words: juicing bids farewell to fibre.
You can see this in the nutrition label of most juices – fibre is usually a sobering zero. At best, juices contain only traces of the valuable fibre you’d get from whole fruit or vegetables.
During a 7-day juice cleanse, the body gets plenty of liquid but virtually no fibre. While a cleanse isn’t a long-term diet (so we wouldn’t expect long-term effects like raised diabetes risk), even a short-term lack of fibre can be uncomfortable for digestion. Fibre is the main food for the bacteria in your gut microbiome.
Did you know? Fibre is almost entirely lost in juicing – yet it’s essential for a healthy gut.
Fruit and veg are rich in micronutrients, but some vitamins and minerals are lost when you only drink the juice. There are also critical nutrients that fruit and vegetable juices don’t provide in meaningful amounts.
Vitamin B12 is essential for the immune system, energy metabolism and the nervous system.⊕⊕ It’s found mainly in animal foods – so not in fruit and veg to begin with. While juices may provide other micronutrients like vitamin C, they lack key vitamins such as B12. If your diet consists only of juices for several days, you’ll get no B12 during that time. If your B12 status was already low, deficiency symptoms could develop without sufficient stores.
Even in their whole form, most fruits and vegetables aren’t the best sources of certain minerals and trace elements. Notably calcium, magnesium and zinc are present only in small amounts – if at all – in many common varieties. A juice cleanse can therefore lead to shortfalls.
In fruit, vitamin E is primarily found in fat-containing structures – especially oils and fatty components (e.g., seeds). In vegetables, it’s located in cell membranes, i.e., in the solid parts of veg such as sweet potatoes or broccoli. Juicing removes significant amounts of this fat-soluble vitamin that would still be present in the whole food. Juices are also low in fat. If no fats are eaten from other foods, the absorption of fat-soluble vitamins (E, D, K, A) is impaired.
Protein and fats provide essential building blocks: amino acids from protein and fatty acids from dietary fat. Many plant foods are excellent sources of both – think legumes, nuts and seeds. With a few exceptions (e.g., avocado), fruit isn’t a meaningful source of protein or fat. Vegetables are similar.
What little protein and fat there is gets reduced to near zero in juice. A typical juice contains neither protein nor fat in relevant amounts.
If juice is just a small part of an otherwise balanced diet, this isn’t an issue because other foods supply protein and fats. But if your diet consists only of fruit and veg juices for several days up to a week, the body gets none of these structural nutrients.
A typical juice cleanse provides only 700–800 kcal per day, creating an extreme calorie deficit of several hundred to over a thousand calories daily – depending on energy needs. In this metabolic state, muscle loss can occur even in a short time as the body compensates for the deficit by tapping into muscle protein.
Yes, such a large deficit can lead to several kilos lost within days. But this isn’t healthy or sustainable if a high proportion of that loss is lean muscle – which can harm your long-term metabolism.
Given the extreme calorie deficit of a juice cleanse, rapid weight loss is no surprise. In just a few days, people often lose 3, 5 or even more kilos. But if you assume it’s all body fat, you’re ignoring human physiology.
Weight loss of 1–3 kg in the first 3 days of a cleanse largely comes from:
A daily deficit of ~800–1500 kcal triggers massive “economy mode” in the body. Basal metabolic rate drops – your resting energy expenditure is dialled down to cope with the deficit.
The body also mobilises reserves. Some of that is fat (depending on body fat percentage), but a lot is glycogen (stored carbs in muscle and liver) and amino acids from muscle protein.
The unintended muscle loss caused by an excessive deficit and inadequate protein intake is problematic. Muscle is the key driver of an active metabolism (specifically: resting energy expenditure). You won’t lose half your muscle mass in a 3–7 day cleanse, but such a deficit shouldn’t become a habit. It’s also sensible to minimise muscle loss – for example, by adding high-quality protein.
The sweeping claims that the body needs regular detoxing via a juice cleanse aren’t backed by science.⊕ Worse: new research ⊕ from 2025 points to negative effects on the microbiome.
After just 3 days of juice fasting, an international research team observed significant increases in bacteria linked to inflammation. Participants who consumed only juice showed the most pronounced negative changes in both the oral microbiome and the gut flora.
The researchers point to the high sugar content and lack of fibre in juice cleanses as likely reasons.
In most cases, a juice cleanse won’t have serious consequences. But you shouldn’t expect special benefits either – there’s simply no evidence. As a kick-off to changing your diet, a brief cleanse might feel motivating, but from a nutrition perspective it should last no more than 5 days and be a one-off – not a regular ritual. And there are better options.
If your goal is “detox”, you can relax: the body is a complex, finely tuned system that detoxifies itself every day – thanks mainly to the kidneys, liver and gut. You don’t need a juice cleanse for that.
If your goal is to lose a few kilos and find a comfortable weight, there are evidence-based alternatives to this kind of crash diet (which is what a high-deficit juice cleanse ultimately is):
https://www.ddg.info/diabetes-zeitung/hoechstens-50-gramm-pro-tag
Klein, A. V., & Kiat, H. (2015). Detox diets for toxin elimination and weight management: a critical review of the evidence. Journal of human nutrition and dietetics : the official journal of the British Dietetic Association, 28(6), 675–686. https://doi.org/10.1111/jhn.12286
Sardaro, M. L. S., Grote, V., Baik, J., Atallah, M., Amato, K. R., & Ring, M. (2025). Effects of Vegetable and Fruit Juicing on Gut and Oral Microbiome Composition. Nutrients, 17(3), 458. https://doi.org/10.3390/nu17030458
Jan Rein is a trained nutritionist and economist, and the author of multiple books on gut health and metabolism. He shares weekly insights on his podcast Heißer Brei and is the author of The Fart Taboo: What Really Helps With Bloating (2017) and Proteins: Why We Need More of Them (2024).
By contrast, a juice cleanse offers:
Our view: if you want long-term results, don’t bank on short-term miracles. Take ownership of your health and make a few, important decisions every day that move you in the right direction.
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