Detox Cure: What Juice Cleanses and Detox Teas Actually Do
There is no such thing as slag in the body. The need behind the idea is still legitimate. Between detox hype and quick mockery lies a third path, and it begins with an honest question: what are you actually looking for when you do a cure?
Most texts about detox make it too easy for themselves. Some sell you a miracle, others laugh at you. Both miss what you are actually saying when you do a cure. That is exactly where I would like to start.
May I ask you an uncomfortable question? When you reach for the juice package in spring, is it really about toxins? Or is it about the feeling that there is currently too much of everything inside you?
I am asking this without irony. That feeling is real, and it is a good signal. The body speaks up when alcohol, sugar, appointments and poor sleep pile up. It is just that this signal has been getting the wrong translation for years. It does not say "there is slag inside you". It says something more like: "Too much has been asked of me."
In this text I separate the two. First we look at what is wrong with the detox myth. Then we look at what is entirely legitimate about the need behind it. And at the end, we look at what may genuinely ease the load on your metabolism, without you having to buy anything for it.
Slag is not a medical term
Let us start with the word that carries half of the detox industry. Slag comes from metalworking. When ore is melted, a glassy residue remains, settles and is skimmed off. A powerful image. It just does not fit a living organism.
In physiology there is no class of substance that settles in connective tissue as an insoluble coating and waits to be dissolved out by a tea. What does exist are substances with clear names and clear routes: breakdown products of your own metabolism, medication residues, alcohol breakdown products, hormone metabolites, fat-soluble environmental compounds.
And for these substances there is no waiting room, there is a conveyor belt. The liver converts fat-soluble substances via a large enzyme family, the cytochrome P450 system. It then couples the intermediate products to carrier molecules and makes them water-soluble. The kidney takes over and removes them from the blood via filtration and active transporters.
A review from the NOVA Medical School in Lisbon describes cytochrome P450 as a cornerstone of xenobiotic metabolism. These enzymes process an enormous range of chemically very different substances, and they do so continuously. For you that means: the machinery a cure supposedly switches on is already running while you read this sentence.
DOI: 10.3390/jox11030007A review in the Annual Review of Pharmacology and Toxicology describes the kidney as a central organ for the excretion of foreign substances. The proximal tubule is decisive, where specialised transporters actively move substances out of the blood into the urine. Excretion is therefore not passive seepage but a highly organised transport process.
DOI: 10.1146/annurev-pharmtox-011112-140317Liver
Converts fat-soluble substances and couples them to carrier molecules. Continuous operation, no start button.
Kidney
Filters the water-soluble products and actively transports them into the urine.
Gut
Carries out the substances shipped via the bile, provided there is enough fibre.
The question is not: "How do I get rid of my slag?" There is none. The better question is: "Have I given my three organs of excretion enough raw material and enough rest so they can do their continuous work well?"
And now you know why an image from the iron foundry does not describe the biology of your body.
What a juice cleanse actually does in your body
Now it gets interesting, because a juice cleanse certainly does something. Usually just something other than what is printed on the packaging.
When you juice, the juice remains and the pulp goes in the bin. With the pulp, most of the insoluble fibre is lost. What lands in the bottle is high in sugar and low in fibre. Exactly the combination your gut is usually missing.
A research group at Northwestern University put 14 people on either pure juice, juice plus food, or plant-based whole food for three days and then examined microbiome samples from stool, saliva and cheek mucosa. The clearest change was in the oral microbiome, with an increase in bacterial families associated with inflammatory processes. The authors attribute this to the combination of a lot of sugar and little fibre. The study is small, so please read it as a signal, not as proof.
DOI: 10.3390/nu17030458There is another point that is rarely explained to anyone: green leafy vegetables are rich in oxalate. Juicing concentrates the amount considerably, because in one glass you drink the leaves of several portions. For most people this is unproblematic. For some it may not be.
The American Journal of Kidney Diseases documents the case of a 65-year-old woman who developed acute kidney failure after a green juice cleanse. The kidney biopsy showed masses of calcium oxalate crystals in the renal tubules. She had risk factors, among them a previous gastric bypass operation and a course of antibiotics that had just ended. A single case proves nothing about the general population. It does show that a juice cleanse is not a zero-risk product.
DOI: 10.1053/j.ajkd.2017.08.002The weight loss that is not one
Something really does happen on the scale during those days. It is just that the rapid loss under strong calorie restriction consists largely of water and emptied glycogen stores. Every gram of glycogen binds several grams of water. Once you eat normally again, both come back.
The second part is less comfortable. After strong restriction, the hormonal setting that steers your appetite shifts. And it stays shifted for quite a while.
A research group at the University of Melbourne put 50 people on a very low calorie diet for ten weeks and tracked their appetite hormones. One year after the diet, leptin, ghrelin, peptide YY and other signals were still altered, and subjective hunger was increased. For you that means: if a cure does not last, it is not a question of character but a biological counter-movement.
DOI: 10.1056/NEJMoa1105816And now you know why the feeling after a cure is so often the same: briefly lighter, then everything as before.
Detox tea: herbal is not the same as harmless
With teas it gets trickier, because many people automatically translate "herbs" into "gentle". A look at the ingredient list of many detox and slim teas, however, often reveals laxative plant compounds, senna leaves and senna pods above all.
The feeling afterwards is unmistakable: the belly gets flatter, the scale shows less. That is not a detoxification effect. It is accelerated bowel movement and fluid loss. Anyone doing this for weeks loses water and electrolytes, not pollutants.
The Annals of Pharmacotherapy describe a case from Brussels: a 52-year-old woman drank a litre of tea made from 70 grams of dried senna pods every day for more than three years. She developed acute liver failure with kidney involvement and needed intensive care treatment. A liver transplant was on the table, and she eventually recovered under treatment. This is an extreme case at an extreme dose. It still shows that anthraquinone laxatives are medicinal substances, not wellness.
DOI: 10.1345/aph.1E670The same logic applies to colon cleansing, which some detox concepts sell as the crowning step. Here too the data have been examined.
A systematic review in the American Journal of Gastroenterology screened the literature on colon cleansing as a general health measure. The authors found no methodologically sound controlled trials supporting the practice, but several case reports of adverse effects. Their conclusion: for general health promotion, colon cleansing currently cannot be recommended. Medically prescribed preparation before a colonoscopy is expressly a different matter.
DOI: 10.1038/ajg.2009.494And what about the cure packages as a whole? Two researchers in Sydney asked that question systematically.
A critical review in the Journal of Human Nutrition and Dietetics examined the evidence on detox diets. The result is sober: very little clinical evidence, and to the authors' knowledge no randomised controlled trials supporting commercial detox programmes in humans. Individual food components such as coriander or nori showed signals of detoxifying properties, mostly in animal experiments though. For you that means: the concept has not been disproven, it has simply barely been studied.
DOI: 10.1111/jhn.12286"There are no studies" is not the same as "it is nonsense". It means: nobody has tested it properly, and it is being sold at a high price anyway. That gap is not your problem, it is the problem of those who promise something without having tested it.
And now you know why, with teas, I do not look at the label but at the ingredient list.
I know this pattern very well. Imagine someone who has been doing a juice cleanse every spring for eight years. Always the same week in March, always the same package, always the same sentence afterwards: "The first days are hard, then I feel great." And always the same question in May: "Why is that feeling gone again?"
When we look at the whole year together, something other than a pollutant question often becomes visible. There is a winter with a lot of alcohol on evenings when the day had been too long. There is food that happens on the side. There is sleep that gets cut first. The cure week is then the only week in the year when all of that pauses.
When something changes in such cases, it is usually not because of a product but because of the look at those other eleven months. I cannot claim causality and am only describing a pattern I observe. The lesson from it is unspectacular: the effect of the cure never came out of the bottle. It came from what was left out during that week.
Why the need behind detox is still right
Now comes the part that critical articles like to leave out. Because if we only say "there is no slag, it is all nonsense", then we miss a real observation.
We do live in an environment that demands a lot of the metabolism. Fat-soluble environmental compounds are real, they are measurable, and they accumulate in fat tissue. That is not esoterics, that is toxicology.
A review in Diabetes and Metabolism describes that persistent organic pollutants accumulate in fat tissue and can enter the bloodstream in greater amounts during weight loss. The rise is more pronounced the faster the weight comes off. Whether a measurable health disadvantage arises from this is not yet clear. The authors discuss it as a possible explanation for unexpected effects after crash diets. For you, this argues for a calm pace rather than a lightning cure.
DOI: 10.1016/j.diabet.2016.05.009This is where the four KPNI lenses interlock. Metabolism supplies energy and building blocks for the coupling enzymes. The immune system reports through inflammatory signals how high the clean-up demand currently is. The hormonal system sends its own breakdown products through the same workshop, for example during estrogen breakdown. And the nervous system co-decides, through stress, how many resources are left for repair rather than for standby alarm.
Especially interesting is the connection between gut and hormone balance. Broken-down hormones are coupled in the liver and shipped into the gut via the bile. There, certain bacterial enzymes can break that coupling open again, so that part of it returns into circulation.
A review in Dermatology and Therapy describes the so-called estrobolome: those gut bacteria whose enzyme beta-glucuronidase co-regulates the reuptake of estrogen from the gut. From this the authors draw a gut-skin axis. For you that means: what happens in the gut can reach as far as your hormonal setting. The gut is therefore not a pipe but a control loop.
DOI: 10.1007/s13555-022-00759-1A research group at UCLA measured estrogens and their breakdown products simultaneously in stool and blood plasma and compared them with the genetic material of the gut bacteria. The number of genes for beta-glucuronidase and arylsulfatase was linked to the amount of free estrogens in stool and partly also to the plasma values. This supports the hypothesis that the gut is a compartment of hormone physiology in its own right. It is an observation, not proof of a cause.
DOI: 10.1016/j.mce.2025.112534Your wish for relief is not naive. It is a good body signal that has simply been given a poor translation. The mistake does not lie in what you feel. It lies in what is being sold to you as the answer.
And now you know why I do not laugh at people who want to do a cure. I would rather ask what they currently need a break from.
What may genuinely ease the load on your metabolism
If the cure is the wrong answer, what is the better one? From my point of view, three things, and none of them comes in a cure package.
First: the raw materials for the second step
The second stage of biotransformation couples intermediate products to carrier molecules. The most important of these is glutathione, a small molecule made of three amino acids. Your body produces it itself when there is enough cysteine available, and cysteine comes from protein.
A review in Nutrition Reviews uses the example of severe undernutrition in children to describe how closely cysteine availability and glutathione formation are linked. Where cysteine was scarce, glutathione synthesis in the red blood cells ran more slowly. That is an extreme model, but it shows the principle: without building blocks, no coupling partner. Protein is therefore not a fitness topic but a raw material of detoxification.
DOI: 10.1111/j.1753-4887.2011.00462.xA review in the Journal of Nutrition describes methionine as the starting point for cysteine formation via the transsulfuration pathway and calls this step rate-limiting for glutathione. At the same time, methionine is the most important methyl group donor in the body. Both tasks draw on the same source. Anyone eating very little protein can get tight here.
DOI: 10.1093/jn/nxaa155A paper in the journal Age discusses that glutathione formation declines with age and that a higher cysteine intake might partly offset this decline. The authors argue that older people with a low protein intake in particular could be affected. This is a hypothesis built from collected evidence, not a finding from a large randomised trial. As a direction of thought, I still find it strong.
DOI: 10.1007/s11357-015-9823-8Second: plant compounds that get your own workshop running at a higher gear
Here there really are human data, and they come from a region with high air pollution. The interesting part: what was measured was not a feeling but the urinary excretion of a pollutant breakdown product.
In Qidong, China, researchers from Johns Hopkins University had 291 people drink either a beverage made from broccoli sprouts or a placebo for twelve weeks. In the sprout group, urinary excretion of the benzene breakdown product rose by around 61 percent, and that of the acrolein breakdown product by around 23 percent. The effect held across all twelve weeks. This is one of the few studies in which a food showed a measurably increased excretion of a pollutant.
DOI: 10.1158/1940-6207.CAPR-14-0103The same research group repeated the experiment with 170 participants and three different doses. Only the highest dose clearly increased benzene excretion, by around 63 percent. Half the dose and a fifth of the dose did not differ from placebo. That is an important damper for all miracle powders: there is a threshold below which nothing measurable happens.
DOI: 10.1093/ajcn/nqz122Third: fibre, which is exactly what the juicer throws away
Substances shipped out via the bile need a transport route to the outside. Fibre binds bile acids and speeds up the passage. And it is one of the best documented nutritional factors there is.
A series of systematic reviews and meta-analyses in the Lancet pooled data from 185 prospective studies and 58 clinical trials. People with the highest fibre intake had a 15 to 30 percent lower risk of all-cause mortality, heart disease, stroke, type 2 diabetes and colorectal cancer compared with the lowest group. The most favourable range was 25 to 29 grams per day. And it is precisely this component that stays behind in the pulp when you juice.
DOI: 10.1016/S0140-6736(18)31809-9"The cure flushes out toxins."
There is no substance waiting for a trigger signal. The conversion runs permanently via liver, kidney and gut.
Raw materials instead of a start button
Protein, sulphur, fibre and plant compounds are what the process consumes every day.
"Seven days for a fresh start."
After restriction, appetite hormones stay shifted for months. An event can hardly change a permanent state.
The effect lies in what you leave out
Less alcohol, less sugar, more sleep. The part of a cure that works costs nothing.
Three levers closer to biology than any cure
- Lower the load instead of buying extras: alcohol is the single biggest lever most people have in their own hands.
- Bring fibre back: eat vegetables rather than drink them, do not throw the pulp away, build in legumes and cruciferous vegetables regularly.
- Take protein seriously as a raw material: without cysteine no glutathione, and without glutathione the second stage lacks its coupling partner.
Where the science ends and my assessment begins
- Well documented: fibre intake and health, the absence of robust studies on commercial detox programmes, the lasting hormonal shift after strong restriction.
- Documented in clear studies, but in a narrow setting: the increased pollutant excretion through a broccoli sprout beverage under heavy air pollution.
- Mechanistically plausible, human data thin: the idea that a better protein and sulphur supply may noticeably support the second stage of biotransformation in everyday life.
- My observation, without a study basis: that behind the wish for a cure there is usually the wish for a break.
And now you know why I do not talk anyone out of a detox cure without first asking what they hope to get from it.
Frequently asked questions about detox cures
Does a detox cure make sense?
As a short cleaning programme for the body, a detox cure does not make sense, because liver, kidneys and gut are working permanently anyway. A critical review found no convincing randomised human trials for commercial detox programmes. What can make sense is the thing many people are unconsciously looking for when they book a cure: a break from alcohol, sugar and heavily processed food, plus more vegetables and more sleep. That part can be put into practice without an expensive cure package.
Is there such a thing as slag in the body?
Slag is not a medical term. There is no class of substance that settles in tissue as an insoluble residue and could be dissolved out by a cure. What does exist are metabolic products, medication residues, alcohol breakdown products and fat-soluble environmental compounds. For these substances there are defined routes: conversion in the liver, excretion via kidney, bile and gut. The word slag comes from metalworking, not from physiology.
What happens in the body during a juice cleanse?
Juicing removes most of the insoluble fibre, and what remains is a liquid that is very high in sugar and low in fibre. In a small intervention study with 14 participants, what changed most after three days was the microbiome in the mouth and cheek, with an increase in bacterial families that are associated with inflammatory processes. On top of that comes a clear calorie deficit. The weight lost in such a short window consists mostly of water and glycogen.
Can detox teas do harm?
Many products contain laxative plant compounds such as senna leaves or senna pods. The medical literature documents one case in which a woman drank a litre of very strongly dosed senna tea daily for more than three years and developed acute liver failure with kidney involvement. That is an extreme case and not a normal course. It does show, though, that herbal does not automatically mean harmless. More common are fluid and electrolyte losses through ongoing diarrhoea.
Why do the effects of a detox cure never last?
Because a cure is an event and your metabolism is a permanent state. After strong calorie restriction, appetite hormones shift measurably. In a clinical study with 50 participants, leptin, ghrelin and other satiety signals were still altered one year after the diet, accompanied by more hunger. That is not weak willpower, it is biology. A programme with a start and an end date can therefore hardly change what grows out of daily habits.
Can a juice cleanse harm the kidneys?
In people with risk factors, caution is appropriate. Green leafy vegetables are rich in oxalate, and juicing concentrates the oxalate load considerably. The literature documents the case of a 65-year-old woman who developed acute kidney failure from oxalate crystals after a green juice cleanse. She had risk factors, among them a previous gastric bypass operation and a course of antibiotics that had just ended. With known kidney weakness, such a cure belongs in a conversation with a doctor.
What is the difference between detoxification and detox marketing?
Detoxification is a biochemical term for biotransformation: the liver converts fat-soluble substances via enzymes of the cytochrome P450 family, couples them to carrier molecules in a second step and makes them water-soluble. The kidney then removes them via filtration and active transporters. Detox marketing uses the same word for a time-limited product and suggests that this process would need to be switched on. It runs without interruption.
Is colon cleansing or colon hydrotherapy of any use?
A systematic review in the American Journal of Gastroenterology screened the literature on colon cleansing as a general health measure. The authors found no methodologically sound controlled trials supporting the practice, but several case reports of adverse effects. On that basis, colon cleansing cannot be recommended for general health promotion. This expressly does not apply to medically prescribed bowel preparation before a colonoscopy.
Can stored pollutants be released during weight loss?
This is the point where the detox idea does touch on something real. Fat-soluble environmental compounds, known as persistent organic pollutants, accumulate in fat tissue. A review describes that their blood concentration can rise during weight loss and that this rise is more pronounced with very rapid weight loss. Whether this measurably affects health is not yet settled. It does argue for a calm pace rather than a radical cure.
What can genuinely support detoxification in the body?
The best documented route runs through food components. In two randomised trials in China, a beverage made from broccoli sprouts increased the urinary excretion of breakdown products of the air pollutant benzene, in the larger study with 291 participants by around 61 percent. The active compound sulforaphane stimulates the body's own coupling enzymes. Added to that are protein as raw material for glutathione, fibre for the gut and bile acid binding, and simply less alcohol.
Why do many people still feel better during a detox cure?
Because a cure usually changes several things at once: no alcohol, no sugar, no fast food, more vegetables, more water, often more sleep and fewer appointments. The fact that this feels good is not imagination. The effect is very likely down to what was left out, not to a powder or a tea. And that is the good news: the part that works is free and permanently available.
Who should avoid a juice cleanse or a fasting phase?
Restraint is appropriate with known kidney weakness, a history of kidney stones, diabetes with medication, eating disorders, underweight, in pregnancy and while breastfeeding, and in children and adolescents. After gastric bypass surgery and when taking several long-term medications, such a plan also belongs in a conversation with a doctor. This text does not replace individual advice or a diagnosis.
Read on in the Detox guide
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On how to read the evidence: The basics of biotransformation and the data on fibre are well documented. Two of the works cited here are single case reports, which show what can happen but not how often it happens. The microbiome intervention study is very small with 14 participants. For the connections around cysteine, glutathione and daily nutrient supply, the statements rest on mechanistic work and reviews. That is biologically plausible, but not yet documented with the same certainty as through large randomised trials. This text does not replace medical advice or a diagnosis.