Thursday, March 6, 2014

The Ultimate Detox: Your Kidneys

The specter of unseen, unspecified toxins eroding our health is worth many millions of dollars in the United States and abroad.  Companies offer "detox" supplements, beverages, and creams that supposedly rid us of supposed toxins, despite a complete lack of evidence that these products do anything at all*.  This comes from an industry that excels at creating boogeymen and offering costly solutions for them.

If your wallet needs to lose weight, then these products are highly effective, otherwise it's probably best to save your money.  Here's why.

The body is equipped with an extremely advanced system for excreting toxins.  The kidneys are part of this system, and their design is genius.  The basic functional unit of the kidney is the nephron, and the average kidney contains about a million of them.  Nephrons have two major parts: a renal corpuscle and a renal tubule

A nephron.  In this image, the Bowman's capsule and glomerulus make up the renal corpuscle, and the proximal/distal tubules and the loop of Henle (#1-3) make up the renal tubule.  Note the network of blood vessels (capillaries) that allow the transfer of water and other goodies from the tubule back into the blood.  Image source.
The renal corpuscle is the interface between the blood and the fluid that will eventually become urine.  Blood is filtered by a fine "sieve" of cells that prevents everything larger than a small protein from passing into the renal tubule.  Red blood cells, platelets, and most proteins stay on the blood side, while small proteins such as albumin, minerals, urea, glucose, water, and almost anything that would be considered a toxin** are allowed through into the renal tubule.

The renal tubule is a long tube that re-absorbs everything in this filtered blood that the body wants to keep.  Water, minerals, albumin, glucose, amino acids, and other useful molecules are re-absorbed.  Everything else ends up as urine and is excreted. 

Can you see the genius of this design?  Urine is blood, minus all the good stuff.  Everything that isn't specifically recognized by the body as useful is excreted by default, no matter what it is.  The body doesn't have to recognize each of the thousands of foreign compounds that make their way into our circulation each day.  These substances are all out the door, by default.

Are you impressed by your kidneys yet?  If not, consider this.  Your kidneys filter your entire blood volume roughly 70 times per day.  The reason you don't have to pee a liter a minute is that urine volume is reduced by 99 percent due to water reabsorption in the renal tubules.

This is why most drugs have to be taken on a regular basis, often several times per day.  In concert with the detoxification enzymes of the liver, which tend to make drugs easier for the kidneys to excrete, the kidneys rapidly reduce the circulating concentration of drugs simply by excreting everything they don't recognize as useful.

Can a detox product improve upon 500 million years of kidney evolution***?  I have my doubts.

* Exception: chelation therapy offered by a licensed medical practitioner for actual, diagnosed heavy metal poisoning.  Second exception: strategies that use the word "detox" loosely to refer to removing unhealthy foods from the diet.

** Toxins tend to be very small-- either small organic molecules or minerals such as arsenic.  Larger toxins such as proteins are uncommon in the circulation because proteins are generally not absorbed by the digestive tract.  Toxic proteins have to be injected or otherwise directly introduced into the circulation, e.g. by a snake bite or a bacterial infection.  But if you're bitten by a rattlesnake, I hope your first line of treatment won't be a detox kit from your local supplement store.

*** Kidneys are present in hagfish and lampreys, the most "primitive" living vertebrates.


davidjhp said...

Great article, thanks.

I was wondering if you have any comment on water filters and water purifiers. We are told that unseen toxins in public water erode our health, and that filters & purifiers will help. Curious if you have any thoughts on this.

Anonymous said...

Hey Stephan,

So, drink water? I thought I needed a cabinet full of potions. ;)

Just curious, what prompted you to write on this topic?

Unknown said...

Whoa, cool post!

Stephan Guyenet said...

Hi WGwin,

I've been reading through my physiology textbook lately and this struck me as a useful and educational topic.

Sanjeev said...

the folks I've run across that do detox type stuff hold the beliefs that call for the detox as one tiny bit of a huge muddy hairball- pull on one hair and all the other strands engage to keep it in place. Most of these hairs/beliefs are total woo- completely illogical views on "energy", "laws of attraction", channeling, biodynamic farming, astrology and so on, almost ad infinitum.

So the rare victim prone to this marketing message may be talked out of detoxes by rationality.

AND, IMHO, that would be RARE.

Deirdre said...

Hi Stephen,

Not that you are ever at a loss for blog topics, but was wondering if I could offer a "request" ;):

I was hoping you could address the controversial new study published in Cell Metabolism this month. It's the study linking high intake of animal protein in middle aged adults with cancer. I would love to hear your perspective as I value and trust your expertise.

Thank you!

Urban Tech Gal said...

Kidneys are such cool efficiency machines. They are the world first recyclers.

Kidney cancer is on a very rapid trajectory upward in young people, and may be pause for commenting on the power of filtration. Sure, lots of toxins can be flushed out of the system, yet petrochemicals, like those found in plastic water bottles, are too big to pass through the membrane....

Kathleen said...

Hello Stephan,
Are there steps one could take to improve kidney and liver function?
I eat organ meats and eggs regularly. I drink fresh organic green juice almost daily (14oz. mixed kale, dandelion greens, daikon, ginger, celery, 2-4Tbl raw potato starch). I eat fermented foods. I avoid nut and seed oils. Packaged foods are out...
If organ function is key, how do we best care for our organs?

Tim said...

A nice and very entertaining appreciation of the tremendous job our kidneys do for us every day (well, except for those unfortunate folks who are on dialysis).

There's plenty of potential for followups, though. The body's "detoxification" systems are of course much more complicated as suggested by this post, as it neither discussed the role of the liver as the body's second major detoxification organ nor the biochemical transformation pathways involved before the kidneys even come into play (e.g. phase I and II enzymes).

This is where "supplements"/over the counter drugs (it's impossible to draw a clear line between both) can indeed have some value. N-acetyl cysteine is routinely used in medical practice to boost the glutathione content of the liver (e.g. as a first-line antidote to acetaminophen poisoning). If you suspect to have eaten death cap mushrooms, you may well save your live by taking a large dose of alpha-lipoic acid or milk thistle extract. There are hundreds of studies showing benefits of milk thistle extracts (silymarin) on a variety of disorders and even improved liver function values (ALT, AST) in healthy persons. Therefore I wouldn't dismiss the potential of supplements to aid in detoxification out of hand.

Paul Warfield said...

Following up on Tim's response, I would add the following. Many very bright and well-educated people in the medical field offer similar arguments about the beauty and efficacy of the colon. They scoff at the notion that colonic therapy could be beneficial.

Well, I suspect that there are many millions of people who have experienced hydrotherapy, and seen marked improvements in their health, who would disagree. I certainly fall into that category, and had no expectations whatsoever when I first underwent such therapy.

I have little doubt that various types of detox are potentially useful, no matter how beautifully designed and highly evolved the human body may be.

Feanne said...

Hi Stephan, Thank you for another informative piece! Go kidneys! :) I'm also curious about Kathleen's question above-- are there any particular foods or activities that specifically help with kidney and/or liver function?

Health Divas said...

What a fantastic summary, just discovered your blog!


Unknown said...

Stephan there is one problem with your post. While I agree that commercial detox supplements are a waste of money, it is a fact that the body does store toxins, including pesticides in adipose and other tissue.

It is also a fact that infrared saunas combined with high doses of niacin have proven detoxification efficacy -


So it is not accurate to say that the body is able to detoxify itself without exogenous assistance.

Unknown said...

Common micronutrient deficiencies, a low protein diet, and exposure to metabolic and environmental toxins can cause toxins to accumulate in adipose tissue and important glands such as the thyroid gland. What are your thoughts on medical detox products that supply protein in combination with high-potency micronutrients involved in the detoxification process? I've had great results using one of these products twice a year, and have had clients report health successes using it as well. Of course, the product I use is not available over-the-counter. It's not a chelation product, however.