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?

Liver 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 don’t care for liver as “liver” at all, but I love braunschweiger, liver sausage and paté. My background (and current profession) is in biomedical research, so organ physiology is fairly familiar. Another great thing to mention about livers is how regenerative they are, capable of healing themselves after incredible physical or chemical insult.

    MaryLouise wrote on May 16th, 2011
    • I agree, pate and liver sausage are excellent. I recently made a video episode on how to make Liver with Dry Sherry. Check it out. I find it to be absolutely delicious. http://clicky.me/5K3p

      Aram Hovsepian wrote on May 16th, 2011
    • I don’t care for liver, either. But I do like braunschweiger with mustard.

      J. wrote on May 16th, 2011
    • I think liver should be a MUST to everyone that should be eating it, that! in my frank opinion is just about everyone. Liver can be used a very valuable source of fairly easy to digest protein, a great source of Vit. A, to better allow for the function of other organs (in our body) and mainly for the conversion of T4 into T3 for proper thyroid function.
      I advocate in the consumption of only grass fed liver only, the consequences of eating conventionally raised organs from animals can be damaging in the long run for most common folk, and immediate for those with compromised health, due to exposure to chemicals and hormone alterations.
      Often people dislike also the flavor and texture, well.. i think that also has to do with the preparation http://clicky.me/5K3p

      ruben wrote on May 17th, 2011
      • “due to exposure to chemicals and hormone alterations”

        Wait, doesn’t that go against what was written in the article?

        Garrett wrote on July 15th, 2011
  2. I am so glad that you posted this because I have often wondered if a “filter” could possibly be as good for me as people claimed!

    Crunchy Pickle wrote on May 16th, 2011
  3. I’m passing this on. My mother in law often gives a similar reason for avoiding liver.

    Katie @ Wellness Mama wrote on May 16th, 2011
  4. Clear, easy to read and relevant info I cannot readily obtain elsewhere. Posts like this are the exact reason why I read MDA! Thank you!

    Dan wrote on May 16th, 2011
    • I agree, very to the point and deals with both sides of the story, not just an “Eat this because it’s good for you and not this because it’s bad.” Thumbs up.

      Nutritionator wrote on May 16th, 2011
    • I concur!

      skeedaddy wrote on May 16th, 2011
  5. Liver and onions is something I hated growing up, but the other day I tried to make it with a grass-fed local-raised calf liver, grass-fed heavy sour cream, and bay leaves/nutmeg for seasoning, and it came out great.

    When it comes to toxins, just as it’s safest to eat ‘small’ fish down on the food chain, I heard it’s safest to eat liver of baby animals (makes sense right? It hasn’t lived very long, so hasn’t had the time to accumulate).

    The ethnic markets sell exotic cuts like liver too, but with Chinese markets I always wonder about the quality… in some cases I’d trust a big brand US supermarket over a Chinese market. But that’s another story entirely.

    Mammoth toppler wrote on May 16th, 2011
  6. I eat grassfed liver routinely. However, I recently picked up some conventional chicken livers and made curry with them. I had an obnoxious allergic reaction, red and itchy and puffy everything.

    What about antibiotics and hormones given to the animals? Could this have been the reason for my reaction?

    Tigerfeet wrote on May 16th, 2011
    • Peri-Peri Chicken livers fried in garlic butter…Aish!

      Mike wrote on May 17th, 2011
      • Mike you wouldn’t be south African now would you?

        Sue wrote on May 17th, 2011
        • LOL – yup…

          Mike wrote on May 17th, 2011
  7. Sometimes I’ll make the classic liver and onions in butter, but my favorite dish (which I have almost weekly) mixes in cubes of beef liver, bacon, 6 eggs and raw milk cheddar. Easy, quick and so savory. It’s tough to beat in my book.

    Primal Pig wrote on May 16th, 2011
  8. Wow that’s some sound reasoning and research as usual!

    Liver from conventionally raised cattle is really gross looking though. It’s so pale. Doesn’t make me want to eat it even if it isn’t toxic.

    Peggy The Primal Parent wrote on May 16th, 2011
  9. I make the best Liver on the PLANET!
    I have converted many Liver haters..LOLOL I also only eat calf liver..obviously the younger the animal the less it can accumulate..and it’s sweet..I eat it once or twice a month and make sure its super fresh!..I look carefully and talk to the meat man…get to know your supplier and start up a friendship with them…everyone likes it when someone cares about them and meat cutters are no exception. LIVER!?..on these lips?..You Betcha!…I like chicken livers with bacon and wursts..and liver spreads with eggs and onions..and and..and..and…GROK ON>>>

    DAVE PARSONS wrote on May 16th, 2011
    • Well Mr Dave, care to share a secret or 2 to your liver? I like dredging mine in coconut flour & sauteing in bacon fat, but what is it you do?

      peggy wrote on May 16th, 2011
  10. What about choosing calf vs. beef liver and or chicken liver?

    Karl Ehlert wrote on May 16th, 2011
  11. I hate the taste of liver. Is liverwurst an acceptable substitute? If not, what is?

    John Sorrentino wrote on May 16th, 2011
  12. When I was a kid, several hundred years ago, my mother fixed liver about once a week. It was cheap, because no one wanted it, so we ate it regularly. As an adult, I rarely eat it. I love liver and always have. I just got out of the habit, I guess. But, I am definitely going to add it to my meal plan again. Thanks, Mark for bringing up some good “old” memories.

    Bull wrote on May 16th, 2011
  13. As a follow up question, does anyone know why liver sometimes turns green after being stored in the fridge?

    Nicky Spur wrote on May 16th, 2011
    • I asked my butcher this and he assured me (fingers crossed) that this happens sometimes. I believe it’s just the oxidation of the high iron content. As long as it smells fine, you’re still good.

      Also I think that not having preservatives this plays a role too.

      Primal Pig wrote on May 16th, 2011
      • I used to worry about the high iron content. For women it’s OK, but generally men don’t need any extra. So I started giving blood as often as possible. I’ve actually read that giving blood is quite beneficial for the donor. In fact, how about a post on that Mark?

        Dave, RN wrote on May 16th, 2011
  14. I don’t eat beef liver, and the only chicken liver I can currently get is from regular, factory chickens. Less than ideal. But I figure if I’m eating the chicken, I might as well eat the liver too. Any info on chicken liver?

    Melissa wrote on May 16th, 2011
  15. I have enjoyed liver only a few times. I ate it all but didnot prepare it correctly. I have about a half dozen lbs. or so of liver, liverwurst, tongue and ground heart ready to be enjoyed. I was never afraid of the toxin issue myself but my family is of course worrysome…

    Has anyone here enjoyed liverwurst?

    Primal Toad wrote on May 16th, 2011
  16. out of curiosity. Have there been any studies comparing the meat to fruit, vegetable, or grain grown in the same metallurgical sites?

    Also are there any resources to let us know if our pastured/grassfed animals are raised near such a site?

    dave wrote on May 16th, 2011
  17. I used to HATE liver. As a kid all I remember was the tough as leather stuff I was served. I tried it again as an adult a couple of years ago from my grassfed supplier. I cook it gently in Ghee, tallow or bacon grease (ghee is best), and while cooking shake on some chili powder and lightly with cayenne pepper. The key word here is to cook gently. Cook over low heat. Cut it open and see that it has a slight red center. Take it out of the pan and it will continue to cook briefly. I’ve found that it’s almost creaming in it’s consistency and delicious!

    So lets here some more liver recipes!

    Dave, RN wrote on May 16th, 2011
  18. I believe liver from ruminants (cows, buffalo, sheep) is healthier than those from pigs or chicken

    Josh wrote on May 16th, 2011
  19. I’ve eaten liver most of my adult life a great treat for dinner or breakfast with eggs. The next day after cooking a chuck roast I save the juice and just add more onions, chop up the liver into strips simmer over low heat for an hour and then it’s dinner with lefovers for breakfast. Thanks for the info about liver I will use it the next time someone comments about it.

    rking wrote on May 16th, 2011
  20. Coincidentally enough, I’m eating liver for dinner tonight! Since last month, I’ve been fixing it for myself once a week as an iron treatment after 16 years being vegetarian. At the farmers’ market last Saturday, I picked up lamb’s liver, which I’ll be trying next week.

    The strong flavor and texture put me off at first, but I’ve learned how to cook it to my tastes. Soak in lemon juice, fry quickly in my cast iron pan, and serve with plenty of caramelized onions.

    I knew that the liver acted as a purification organ, in terms of processing materials for excretion from the body, so I wasn’t afraid to eat it. The data presented here on toxin accumulation throughout the body are very compelling and I hope will convert some people to the great nutritional benefits of liver.

    Melly Sue wrote on May 16th, 2011
  21. very interesting post

    Frederik wrote on May 16th, 2011
  22. I have a frozen liver I’ve been grating up occasionally into ground beef. I don’t even notice it! I tried eating it “straight up” and just did not like it much. First couple bites were fine, then the gagging started.

    Same deal with heart – you’ve gotta sneak it in!

    Graham wrote on May 16th, 2011
    • I had the same experience…the first bite or two I could handle fine, but after that I had to fight to get it down. I think I must not have prepared it right.

      Patience wrote on May 17th, 2011
  23. Very helpful post! I’ve wondered the same thing!

    Alyssa wrote on May 16th, 2011
  24. I actually enjoy the taste of liver.. You can soak it in milk before cooking which will make it taste less strong.. But I generally don’t bother, just fry it briefly in some ghee or butter, with onions and apples – typically once a week.

    I’ve been experimenting with eating a little bit of it raw whenever I cook some.

    The Primalist wrote on May 16th, 2011
  25. I hated liver growing up. My grandmother would often make liver and onions but I just couldn’t eat it. I’d eat most other organ meats, just not liver. When I was pregnant I started taking dessicated liver capsules rather than attempt to stomach the stuff. Then when my oldest started eating solid foods I made liver pate from pastured animals. If you have kids you know, what your kids eat you eat, especially when they are first learning to eat. Well, darn if my pate wasn’t pretty darn tasty. So I tried grass fed liver and onions and it was delicious, even when my grandmother made it. All those wasted years avoiding liver when all I had to do was get better quality stuff.

    Sarah wrote on May 16th, 2011
  26. If people used the same filter logic, shellfish would be equally bad (which it isn’t) as all require any and all toxins/food to be filtered through.

    James wrote on May 16th, 2011
    • One New Year’s Eve while working in a restaurant, a coworker remarked as he was slurping down some lobster, “I love poop-eating fish, in butter”

      peggy wrote on May 16th, 2011
      • haha, that is great, and so true!

        Hilary wrote on November 14th, 2011
  27. Yikes!! I come from Lahore, Pakistan and most of my relatives still live there. My dad was in the poultry farming business for two decades and owned one of the largest farms in the country.

    The results of this study are very worrying given how heavily meat based the Pakistani diet is. We love our meat and will eat it at virtually every meal. Each time my husband and I visit, we have our fill of all our favorite meat dishes. They
    are SO delicious! Perhaps it’s time to exercise
    some caution. Thanks, Mark. I will be forwarding this post to my family.

    Sabrina wrote on May 16th, 2011
  28. Still don’t like it. Anyway, my conventional housemate hates the smell, and even the thought of liver. So I would have to cook it when she was away. And those rare times, I am going to cook shellfish, which she can’t eat.

    Harry wrote on May 16th, 2011
  29. I eat a half pound of local, organic, pasture raised beef liver weekly. Love it! Pan-fried with lots of onions, and peppers! Spectacular! Liver, whether it is from CAFO or pasture animals, is always cheap and nutritious! A super-food!

    Zed wrote on May 16th, 2011
  30. When I first started eating primal I craved liver like crazy. I was so nutrient starved that I gulped down an entire beef liver weekly…and they’re huge!

    After about 7 months or so the craving wore off and I started eating ‘normal’…lol. I always wondered if I did myself harm consuming that much liver (it was grassfed/finished), good to know liver is a processing plant and not a filter.

    My mother really knew how to fudge up liver good…dry and totally ‘liver flavored’. I soak mine in milk for 30 minutes and don’t add sea salt until the end, ’cause salt will dry it up. Also, my mother cooked it in Mazola Oil….yuck. I cook mine in Kerrygold Butter and it’s soft and juicey.
    I sometimes add a raw egg yolk or raw cheese into my onions and liver…very yummi :-)

    Suvetar wrote on May 16th, 2011
  31. get some fresh “calves” liver..nice and bright red..not dark or green or any other color…get some bacon..and a nice big Vidalia onion..dice the Bacon -If Im cooking 3-4 nice 3×7 slices I use 1/2 to a whole pound and start to fry it up..when its half done add the chopped up onion and finish the bacon..which should get that onion nice and browned up good..medium heat so as to not over cook either one.Remove from the pan and drain off most but not all of the bacon fat..then turn up the heat a bit. Add the liver slabs and sear a nice brown curb on each side. Dont walk away..be attentive to your food!
    TURN DOWN the heat and put the bacon and onions back in..toss em around and and cook gently until the liver is slightly firm and just hot inside..It does not take long and its ok for it to be pink from edge to edge like a fine steak..Add a couple tbs. of butter and melt it in..Turn it out and eat it up..it will be sweet and mildly creamy and not even anything like your thinking about from the past nightmares of Liver land…GO ahead..try it..this recipe is THE BOMB!

    DAVE PARSONS wrote on May 16th, 2011
  32. Thank you for answering

    Tom wrote on May 16th, 2011
  33. I just read this article:
    http://nevertooldforcrossfit.blogspot.com/2011/05/paleo-diet-pros-and-cons-yeas-and-nays.html
    which addresses the Paleo diet and the toxins etc…in commercial meats.

    karen wrote on May 16th, 2011
  34. I eat about 1 lb of liverwurst a week. Good stuff.

    Eric wrote on May 16th, 2011
  35. I eat goat liver-kidney-heart about once a month. I enjoy the taste but limited the consumption of liver during pregnancy due to its high vitamin A content.

    maba wrote on May 16th, 2011
    • Per a midwife and an OB seen at separate times during separate pregnancies: avoid too much beta-carotene but do eat liver at least once a week during pregnancy. The vitamin A in liver is safe, too much beta carotene is not.

      Sarah wrote on May 19th, 2011
  36. strange. yesterday I made liver for the first time. (it was super cheap.. well as cheap as pastured chicken meat gets).
    I loved it.
    That was until I stopped loving it. And that suits me just fine. It may be that when you hit your threshold it is time to put it aside.
    also, it seems to be tastier the less it’s cooked.
    thanks, as always the information is greatly appreciated.

    patrick wrote on May 16th, 2011
  37. what about the cows u see in fields by the side of the highway. just think how much heavy metal comes out of all those exhaust pipes and will settle on the grass. any info on this?

    lead wrote on May 16th, 2011
  38. Is liver pills any good?

    Darius wrote on May 17th, 2011
    • since i can’t bring myself to eat liver i reverted to taking desiccated beef liver pills. i have taken them for approx 2 months now, and i think they are a very good addition, especially if you are iron deficient. most women are, i guess.

      i’ve been primal only for about a year now, and after having been a vegetarian for 23 years the iron stores in my body were severely depleted. my MD recommended i supplement with liver pills. i looked into the subject and found some interesting articles on them.

      my MD told me that it was virtually impossible to lose any weight with iron levels lower than 30 ng/ml. when i was first tested my levels were around 7 ng/ml, i had no energy whatsoever, and so i was put on a bi-weekly iron supplementation IV drip. interestingly, my weight only started to drop recently. my levels are around 100 ng/ml now. so of course i take my liver pills :-)

      Nica wrote on May 17th, 2011
  39. here is probably the ultimate liver recipe as prepared by people from the valley of Ossau, all you need is a little time..

    http://goo.gl/joVwT

    Mr Vit wrote on May 17th, 2011
  40. Mark,

    Thanks for the reply and clearing up that liver question for me. I guess I will have to take another look at this topic. Maybe find myself some grass fed liver and then try it again. Its been about 30 years since my last meal of liver, and that had to be smothered in onions to make it palatable for me.

    Thank you.

    Chris wrote on May 17th, 2011

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