Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
16 May

Dear Mark: Does the Liver Accumulate Toxins?

liverLiver confuses and confounds many of us. It looks weird, gives off an odd mineral smell, and has a unique texture. We try to reconcile our horrible memories of Mom’s bone-dry renditions of the stuff with all the ethnographic literature describing how hunter-gatherers share precious slivers of the raw trembling organ immediately after a kill. We appreciate and acknowledge the superior nutrient profile of four ounces of beef liver compared to five pounds of colorful fruit even as the shrink-wrapped grass-fed lamb liver direct from the organic farm sits in the freezer untouched. And then we wonder whether it’s even safe to eat, because, you know, it’s the “filter” – the only thing standing between an onslaught of environmental toxins and our vulnerable bodies – and filters accumulate the stuff they’re meant to keep out. See colanders, coffee filters, water purifiers. Liver, then, is many a Primal eater’s Everest. Tantalizing but fraught with seeming danger. Okay, the question:

Mark,

I was reading your post about organ meats. I have always heard liver was nutritionally valuable, but I hear the same thing about bread.

Maybe I am wrong, but isn’t the liver a filter? Doesn’t it filter poisons and toxins from the body?  If I eat liver, am I ingesting the poisons and toxins of the animal? Seems to me there will always be residual poisons in liver. What are your thoughts on this?

Chris

To call the liver a simple filter is incorrect. If we want to maintain the metaphor, it’s more like a chemical processing plant. The liver receives shipments, determines what they contain, and reacts accordingly. It converts protein to glucose, converts glucose to glycogen, manufactures triglycerides, among many other tasks, but its best-known responsibility is to render toxins inert and shuttle them out to be expelled – usually in the urine via the kidney. It doesn’t just hang on to toxins, as if the liver is somehow separate from the body and immune to contamination. The liver is part of the body! If your liver contains large amounts of toxins, so do you!

Okay, so we’ve established that the liver is a processing plant by design, rather than a physical filter whose express purpose is to accumulate toxins, but what about animals raised in industrial, intensive operations? The liver from a pasture-raised cow with a perpetually cud-filled maw can undoubtedly handle its relatively light toxic load; the liver from a CAFO-cow feeding on grain and exposed to environmental pollutants is surely another matter entirely. Right? Sorta, although it’s more complicated than that.

The liver can definitely accumulate heavy metals, but it is not alone in that, nor does it always particularly excel. A 2004 study (PDF) of liver, kidney, and lean meat from cattle, sheep, and chickens randomly selected from ranches in Lahore, Pakistan, found that all three tissues accumulated significant amounts of certain metals. Let’s see how the metals were distributed throughout the various cuts of beef, since that’s what most of us are eating for liver:

Beef liver contained 52 ppm arsenic, 0.42 ppm cadmium, 2.18 ppm lead, and 31.47 ppm mercury. Beef kidney contained 47 ppm arsenic, 0.9 ppm cadmium, 2.02 ppm lead, and 50.65 ppm mercury. Beef lean meat contained 46.46 ppm arsenic, 0.33 ppm cadmium, 2.19 ppm lead, and 62.39 ppm mercury. So, liver accumulated the most arsenic (but not by much), less cadmium than kidney but more than lean meat, and significantly less mercury than kidney and especially the lean meat. All three cuts contained roughly equal levels of lead.

However, another study (PDF) on cattle raised on pasture in the vicinity of metallurgical plants (and their fallout) in the Slovak Republic found that the liver did accumulate significantly higher concentrations of lead, cadmium, copper, zinc, iron, and nickel than muscle meat. What does this tell us? Don’t eat heavy metal contaminated beef, especially liver and kidney; any and all cuts of the animal will accumulate dangerous levels of heavy metals if the animal is exposed to inordinate amounts.

Another study (PDF) examined how aflatoxin, when fed to a cow, was distributed throughout the animal’s tissues, with particular emphasis on the internal organs. Researchers dosed a 160 kg calf with 52 mg aflatoxin per day for five days, then slaughtered the animal and analyzed its tissues for aflatoxin levels. Aflatoxin was found in all cuts, but it was concentrated mostly in the kidneys and, to a lesser extent, the liver. Lean muscle meat contained 12.9 ng/g aflatoxin, heart contained 16 ng/g, spleen contained 18.5 ng/g, kidney contained 145 ng/g, while the liver contained 47.1 ng/g. So, eating a 100 gram portion of liver from this calf would give you 4.6 mg aflatoxin, which is pretty high. Not enough to kill you (the LD50 for baboons is 2 mg/kg bodyweight) on the spot, but it’s probably enough to cause some problems if you make eating aflatoxin-contaminated beef liver a regular habit. Luckily, commercial cattle ranchers aren’t dosing their cattle with 52 mg aflatoxin per day, and aflatoxin doesn’t occur naturally in pasture. It’s a mold that grows on grain stored in damp, humid conditions. Corn, especially improperly-dried corn stored in tropical or sub-tropical regions, is particularly susceptible to aflatoxin.

Those are the worst-case scenarios. Either the researchers purposely dosed the test animals with massive amounts of toxins or they selected subjects from heavily-polluted areas. Most meat and liver you get comes from animals raised in comparatively cleaner (if not more humane) conditions. Not even the staunchest corn-and-candy feeding cow ranchers want their animals eating aflatoxin-contaminated corn or munching on lead-and-mercury infused feed. It would be bad for business and they monitor this type of thing.

Still, people worry. Just to be sure, let’s take a look at studies on toxin accumulation in the livers of free-living livestock, as opposed to livestock living in contrived conditions. One study, which looked at cadmium, lead, and mercury levels in the organs and meat of healthy horses, cattle, and pigs, found that heavy metal accumulation was generally higher in the liver but not enough to affect human health. Another examined lead and mercury residues in livers and kidneys of Canadian chickens, cows, and pigs; all levels were below the official Canadian tolerance of 2 ppm for lead and 0.5 ppm for mercury. Both studies are from the mid-70s, but more recent studies looking at mercury accumulation in cattle have had similar results. Livestock, even CAFO livestock, just aren’t exposed to toxic levels of heavy metals.

Liver can accumulate toxins and heavy metals, but so can every other part of the animal. If you avoid liver because of toxins, you should probably avoid the rest of the animal, too. Besides, liver isn’t an everyday type of cut. It’s high in vitamin A and copper, high enough that eating a half pound a day is excessive and counterproductive, even without any toxins getting involved. Note that an animal only has one liver, and eating large amounts of it every day is evolutionarily novel. Traditional cultures didn’t prize liver because it was easily obtainable in large amounts, you know. It was a nutrient-dense treat, so consume it accordingly – as a weekly delicacy to be savored and enjoyed. As long as you’re avoiding animals in polluted, toxic environments (and I’m not talking CAFOs here; I’m talking industrial waste and heavy metal runoff) eating contaminated food (which you should be doing anyway, even if you don’t eat liver!), liver is a safe addition to your diet. Livers from organic, pasture-raised animals are obviously going to be tastier (almost sweet, in my experience), more nutritious, and cleaner, but I think you can safely eat the occasional liver meal from conventionally raised animals, too.

How often do you eat liver? Are you worried about toxins? Did you realize the liver isn’t like a simple filter, but instead like a processing plant?

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. I hate to admit it… but I’m a bit scared of eating liver. I’ve never had it, and I’ve always been told how gross it was. Mom never even allowed it in the house – all my friends thought I was so lucky. LOL

    I did (accidentally) find out as a teen that I actually liked liverwurst, so I bought a little tube of it at the deli the other month. Wow! I still like it, and I love it with my fried eggs. OMG, so good.

    So I guess it’s time to try some calves liver.

    skookum wrote on May 17th, 2011
  2. The first rule of liver is: Don’t cook it to death! I can recall coming home and knowing via smell (all the way out in the back yard) that we were having liver for dinner. It was so tough it was hard to cut with a serrated steak knife.

    After much persuasion a friend cooked liver that was same day fresh from the butcher shop (they didn’t have vacuum sealed packs back then and six month old frozen liver wrapped in white paper is already starting at a disadvantage) and not overdone to the consistency of leather.

    James wrote on May 17th, 2011
  3. I put my livers in a blender with an egg, and some seasonings,garlic, and some onion, then blend until it’s smooth. Then, I fry it, it fries up like hamburger. After that, I mix it up with roast vegetables, and serve it all in a casserole dish. Even my husband and kids can’t complain. I never liked liver, but I ate it anyways. Now….. It’s the tastiest way I’ve found so far, and it’s very tasty!!!

    Grainne wrote on May 17th, 2011
  4. I JUST LOVE THE LIVER RECIPES I’M READING ABOUT…!!
    GROK ON>>>>>

    DAVE PARSONS wrote on May 17th, 2011
  5. The important thing to realize here is that liver filters everything in the blood coming from the GI tract that has been absorbed, including toxins. Liver doesn’t store toxins. Liver stores the good stuff (ADEK), glucose, etc. So if we eat liver from a good source, we are eating good stuff. I personally would never buy conventional liver, though.

    Meagan wrote on May 17th, 2011
  6. This post was written exactly for me. I kept reading about all the benefits of liver, but when I talked to people about it, they would always say things like, “Ewww…the liver filters all the toxins, I wouldn’t eat that, that’s gross”. This was exactly what I needed to really understand liver as a food instead of a nasty toxin filter.

    Patience wrote on May 17th, 2011
  7. I grew up eating liver and onions (on crackers) and never could understand why other people hated until I tasted the way other people prepared it. I always stuck with chicken liver, and like others have said the trick is to use mild, fresh, high quality liver and not to cook it until it is hard. Also, most importantly, use a cast iron skillet like my mom did! I don’t know why, that’s just what I learned from trail and error. I use a small one, but nothing else cooks it like cast iron.

    I usually use twice or more the amount of onions as liver, and saute the onions first with butter so the liver doesn’t get too hard. The onions should be caramelized and the liver soft when you are done. Oh, and I finely dice the liver as well, though not too fine.

    And it’s great to add flavoring. If you use any alcohol, a tiny splash of white wine and freshly chopped lemon thyme I find work well. Other times I flavor with mushrooms and bacon.

    Grainless though, I don’t know how to replace the crunchy crackers. That’s the one thing that I think more traditional liver and onions misses, something crunchy to scoop it out of the still hot skillet with…

    Amber wrote on May 17th, 2011
  8. Whoa, it’s like you were reading my mind. I was just trying to get someone to try liver and they are all worried it’s toxic. Nice timing! :)

    Nerkles wrote on May 17th, 2011
  9. Never even thought about livers being bad for you.

    Paleo Josh wrote on May 17th, 2011
  10. My doctor told me that he has a friend who works in the meat industry who told him that most livers these days are riddled with cancer. He wanted me to avoid them. I don’t though. I just eat liver from organic pasture-fed animals (lamb mostly).

    Kitty wrote on May 18th, 2011
  11. I love your articles! Too often I read one of your articles and realize that I’ve held onto a tidbit of conventional wisdom without realizing it!

    Angela wrote on May 18th, 2011
  12. Hmm, I eat up to 0.6 lb of beef liver 4 times a week..and I’m wondering now whether it’s too much.

    Phil wrote on June 12th, 2012
  13. It’s good to know about these studies indicating the presence of heavy metals in all kinds of animal fats. I was doing some research on exactly how much heavy metals accumulated in animal meat and am pleased to learn it’s not that high. Thanks for this absolutely excellent post, and putting all the research into one place.

    JustinK wrote on August 18th, 2012
  14. I am not too sure I buy into the whole “Eat small amounts of liver” camp. Seems like it was prized because it was nutrient dense and it was rare. So why hold back on such a treasure?

    Maybe you could elaborate a bit more on why its counter-productive to eat a half a pound of liver a day?

    I can envision a scenario where a human would eat that much: Imagine an extremely fit/intelligent/active human who ends up being an exceptionally good hunter, and is also the alpha male of the group. He would get more than his fair share of whatever he wanted. If the most prized was the liver, then he would get that, in large amounts.

    Maybe the unfit/sickly humans would get very small amounts of it.

    I’ve just recently started eating beef liver. Last night I ate a pound of beef liver in one sitting, yes a POUND. (I’ve never been one to practice caution.) Last night I slept like a baby, and today, I feel like superman. More energy than i have had in years. I’ve done this on three occasions in the past couple of weeks and have had the same results each time.

    Why I should stop?

    Gabe wrote on February 22nd, 2013
  15. Thank you for the processing plant metephor to replace the filter one. So much better! Love being armed with better info.

    Laura M. wrote on February 26th, 2013
  16. I’ve read your blog many times in the past, so when I was searching for info on whether the benefits of eating liver outweigh the potential downsides, I knew I could trust your perspective!!

    We ate liver last night. It had been so many years since I’d eaten it – maybe even since I was a kid. My husband loves liver and onions Mexican style – jalapenos or serranos, onions and mushrooms, even. I smother mine with cheddar chesse (okay, not 100% paleo like I should be eating, but it helps with the taste ;).

    Naomi wrote on April 24th, 2013
  17. Does the Liver Store Toxins? | Mark’s Daily Apple

  18. Thank you for the article! This question came up last night in a conversation.

    As a person who can’t stand the taste/texture of liver, I desiccate (dry, powder and encapsulate) beef liver to take as a supplement – one I do not have to taste!
    Hadn’t thought about chicken livers. I raise chickens and would love to make use of more of their nutritious insides.

    *Question – Does calf liver have the same nutritional values as grown beef liver?

    Erin wrote on January 21st, 2014
  19. Prepare our liver this way and you will actually look forward to your weekly liver night. Slice red or white onions into thin slices and fry in a skillet with bacon fat and/or butter. Add balsamic vinegar, a splash of red wine and reduce. While they are becoming transparent and soft chop about five or six dried figs into tiny cubes, and add to the onions. Fry up until it all becomes tender. Next, dredge your liver slices in almond flour ( or coconut flour, but almond is more decadent). One of the miracles of liver is that it is extremely fast cooking, you really only need a minute a side if the skillet is nice and hot. Fry the liver quickly in bacon fat or olive oil, Top with the onion fig mixture. The balsamic glaze does something to offset the liver taste that many people find objectionable, while the figs add a sweetness that complement it beautifully. Of course, the fresher and more locally raised your grassfed liver, the better it will be. Eat up!

    DukeofUrl wrote on March 20th, 2014

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