Detox and "toxins": what the liver and kidneys actually do

The feeling of heaviness, bloating, and being "clogged up" is familiar to almost everyone, and the word "toxins" explains it faster than any other. Usually, a detox course is suggested next. It is easier to look at what the body actually eliminates, how, and through which pathways—and where juices, teas, and enemas fit into this scheme.

A word without a definition and the feeling behind it

"Sludge" (or "toxins") is not a medical term. There is no substance designated by it, no test that would show its level, and no organ where it supposedly accumulates. Physiology textbooks list end products of metabolism: urea, creatinine, bilirubin, ammonia, and carbon dioxide. Each of these is measurable, each has a known excretion pathway, and none is described as accumulating sludge.

However, the feeling is real. Heaviness after several days of overeating and alcohol, evening swelling after salty food, and lethargy due to lack of sleep are reproducible states with clear causes. The problem with "toxins" is not that they describe a fiction, but that they substitute one cause for several different ones and suggest a solution that does not address any of them.

The liver: two phases, not a filter

The liver is usually imagined as a sieve that traps dirt and gradually gets clogged. It is actually structured differently: it is a chemical plant that rearranges molecules so they can be excreted.

The problem with foreign substances—drugs, plant alkaloids, combustion products—is that they are fat-soluble. Such a molecule passes freely through membranes and, once in the kidney, is immediately reabsorbed. It can only be excreted by making it water-soluble, and this takes two phases.

Phase one is oxidation by enzymes of the cytochrome P450 family in liver cells. The enzyme inserts oxygen into the molecule, creating a chemically active site: a hydroxyl, amine, or carboxyl group. The substance itself often becomes not safer but more aggressive at this step—the first phase prepares it for the second, rather than neutralizing it.

Phase two is the attachment of a large water-soluble residue to this site. Most often this is glucuronic acid (via UDP-glucuronosyltransferase), sulfate, glutathione, or less commonly glycine or an acetyl group. The resulting conjugate no longer dissolves in fats, does not pass back through the membrane, and leaves with urine or bile.

A classic example of both phases is acetaminophen. Most of it immediately binds to glucuronic acid and sulfate and is excreted, but a small portion passes through P450 and turns into reactive NAPQI. In a normal dose, glutathione intercepts it. In an overdose, the glutathione supply runs out, and NAPQI damages liver cells—hence liver failure after taking too many fever-reducing pills.

The main property of this system for the detox topic is that it does not turn on and off. Enzymes of both phases work continuously, their quantity changes over days and weeks, and no drink "starts" them. However, they can be slowed down: furanocoumarins in grapefruit juice inhibit CYP3A4 in the intestinal wall and liver, and against this background, the concentration of several drugs in the blood increases. Freshly squeezed juice in this sense interferes with detoxification, but not in the way advertising promises.

Kidneys, intestines, lungs, skin

What the liver has made water-soluble is taken up by the kidneys. The glomerulus works by a pressure gradient: plasma is pushed through a filter that retains cells and large proteins and lets water with dissolved small molecules pass through. About 180 liters of primary urine are formed this way per day. Then the tubules return almost all the water, glucose, and necessary salts to the blood, and some substances are additionally secreted into the lumen by special transporters. About 1.5 liters are excreted.

Other pathways supplement this. With bile, the liver dumps bilirubin and large conjugates into the intestines, which leave with stool. The lungs excrete carbon dioxide and everything volatile—part of the ethanol, acetone during fasting, hence the characteristic bad breath. The skin excretes water and electrolytes: trace amounts of metals are found in sweat, but compared to the daily work of the kidneys, this portion is negligible.

None of these pathways has a storage reservoir that needs to be periodically emptied. An organism whose liver and kidneys are working excretes continuously; an organism whose organs are not working is treated in a hospital, not with juices.

Juices, fasting, and the first two kilograms lost

A detox juice differs from a fruit in one way: it has no pulp. Along with it goes fiber, which slowed down stomach emptying and sugar absorption, while a liquid with 8–11 grams of sugar per 100 milliliters remains—that is, about the same as in sweet soda. A liter of such juice per day provides a noticeable sugar load without satiety. A separate caveat applies to juices from spinach, beets, and rhubarb: they are high in oxalates, and cases of acute kidney injury have been described after several days of such a "cleanse."

Water fasting usually provides a quick and convincing weight loss, and its mechanism is entirely water-based. The glycogen store in the liver and muscles is several hundred grams, and each gram holds about three grams of water. As glycogen is spent, water leaves with it. In parallel, insulin drops, and subsequently, the kidneys begin to excrete sodium and water more actively. Plus, the intestines are emptied. In total, this easily provides 1.5–2 kilograms in three days.

Everything returns exactly the same way. With the first normal meals, glycogen is restored, water returns with it, sodium is retained—and the scale shows the previous figure in two to three days. Adipose tissue changes by mere hundreds of grams over such a period and has almost nothing to do with these fluctuations.

Teas, enemas, sorbents

"Cleansing tea" almost always means senna, less often buckthorn or rhubarb. Their anthraglycosides are inactive on their own: they are broken down by bacteria in the colon, and the breakdown product increases motility and forces the wall to secrete water and electrolytes into the lumen. After 8–12 hours, this produces a stool. What comes out is the contents of the intestines and water, not something accumulated in tissues.

Regular intake costs potassium, and its loss is doubly dangerous when combined with diuretics or cardiac glycosides. With prolonged use of senna, melanosis of the colon develops—a harmless and reversible darkening of the mucosa, but one that clearly shows that the "tea" acts on the organ like a drug. A decrease in effect and the need for a dose increase have been described. In Russia, such teas are sold as dietary supplements, and labeling according to TR TS 022/2011 does not allow claims about therapeutic properties—which is why the effect is described with the vague "promotes cleansing."

Hydrocolonotherapy is the flushing of the colon with tens of liters of fluid under pressure. The risks should be stated directly: bowel perforation, electrolyte imbalance, and water intoxication, infection from poorly processed equipment; deaths have been reported. The procedure has no proven indication outside of preparation for certain examinations.

Sorbents stand apart in this list because they really work—but only in the intestinal lumen and only with what is there. Why this does not provide a "cleansing course" is analyzed in the article about activated charcoal.

What is called detoxification in medicine and who is "detox" dangerous for

Real detoxification exists, and it is an intensive care procedure. Antidotes work against a specific poison: N-acetylcysteine restores the glutathione supply in case of acetaminophen poisoning, naloxone displaces an opioid from the receptor. Hemodialysis removes from the blood what the kidneys can no longer excrete themselves—in cases of kidney failure, methanol, ethylene glycol, or lithium poisoning. All these methods have one thing in common: they are used for acute poisoning or organ failure, are prescribed in a hospital, and have nothing to do with the lifestyle of a healthy person.

Home "detox" is far from always harmless. Situations in which it is directly dangerous:

• Diabetes. Fasting while on insulin or sulfonylurea drugs is a risk of severe hypoglycemia, and a juice day is the opposite extreme with sharp glucose spikes.
• Kidney disease. Fluid and food restriction, oxalate juices, and electrolyte loss hit an organ that is already working with a lower-than-normal safety margin.
• Diuretics and laxatives together. Potassium loss adds up, and heart rhythm disturbances are closer than they seem.
• Lithium drugs. Dehydration and sodium loss force the kidney to retain lithium, and its concentration in the blood enters the toxic zone.
• Pregnancy. Neither fasting, nor stimulating laxatives, nor colon cleansing are considered here.
• History of eating disorders. "Cleansing" easily becomes a socially approved form of restriction.

The general rule is simple: a sharp restriction of food against the background of a chronic illness or constant medication is a reason to talk to a doctor, not to look for an answer in an article, including this one.

What helps when heaviness is truly present

If we start not from "toxins" but from the listed causes, the set of actions turns out to be boring and effective.

Sleep. Lack of sleep shifts appetite and carbohydrate tolerance after just a few nights, and the feeling of being run down from detox stories most often comes from here. The mechanism is analyzed in the article on how lack of sleep affects weight and appetite.

Water. Not in liters on a schedule and not "for flushing," but simply to avoid being dehydrated: the kidneys need volume to excrete what is dissolved.

Movement. Walking speeds up venous and lymphatic drainage and removes evening leg swelling faster than any tea.

Less salt. Swelling after salty food is water retained by sodium, and it goes away on its own in a day or two if salt is returned to the usual amount. Most of it comes from ready-made food, not from a salt shaker.

Less alcohol. Ethanol dehydrates, worsens sleep, and loads the liver with real work—here the connection to well-being is direct and noticeable.

There is no list of superfoods in this list intentionally: no product that would accelerate the second phase of conjugation or glomerular filtration has been described. However, something else is almost always visible—what changed in the diet a week before the "heaviness." The answer to this question is provided not by a cleansing course, but by a few days of honest tracking of what was eaten.

Count it from a photo

Frequently asked questions

Do I need to cleanse my body of toxins?

The substance known as "toxins" does not exist in medicine: it has no clinical analysis, nor is there an organ where it accumulates. Metabolic waste products—urea, creatinine, bilirubin—are continuously removed by the liver and kidneys without the need for courses or reminders.

Do detox juices help with weight loss?

Weight drops due to water and intestinal content and returns within two to three days after resuming normal eating. Juice without pulp contains 8–11 grams of sugar per 100 milliliters and almost no fiber, so it does not provide satiety.

Can I drink senna tea to cleanse my bowels?

Senna is a stimulant laxative: it increases motility and removes water and electrolytes, not accumulated substances. Regular use depletes potassium, which is especially dangerous when combined with diuretics or heart medications. Such teas should not be used during pregnancy.

Is it true that toxins are released through sweat?

Sweat is primarily water and electrolytes. Trace amounts of metals can be found in it, but compared to what the kidneys excrete daily, this amount is negligible. Saunas and workouts remove fluid, not toxins.

How can I cleanse my liver after a feast?

The liver does not need cleansing: it converts substances into a water-soluble form using two phases of enzymes and does so constantly. You cannot speed up the process with food or drinks; time, sleep, and avoiding further alcohol intake are what help.

Read next

• Activated charcoal for “detox”: what it actually binds — Activated charcoal is cheap, sold without a prescription, and taken for almost anything: the morning after, a weekend cleanse, sometimes a course of capsules for weight loss.
• Alkaline water and “an acidic body”: what the stomach does to it — People talk about “an acidic body” as though it were a condition you can acquire from the wrong breakfast and correct with the right water.
• Myths about food additives and GMOs — Two things on packaging cause the most fear: codes with the letter E and the acronym "GMO.

This article is for general information. It is not medical advice, a diagnosis, or a prescription for treatment or a diet, and it does not replace a consultation with your doctor. If you have a health condition, are pregnant, take medication, or follow a diet prescribed to you, decisions about food belong with your doctor.

Figures from regulations, guidelines and studies are given as they stood when this article was prepared and may since have changed; check them against the primary sources. This article is not advertising, an offer, or individual advice, and neither the author nor the site owner is responsible for decisions taken on the basis of it.