A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Is liver good for you? Isn't it full of pesticides?

January 7, 1983

Dear Cecil:

For those few of us who actually like liver, and for those many others who live with mama and are force-fed the stuff, should we eat it or not? I presume mothers aren't lying when they say it's a good source of iron. On the other hand, wouldn't liver be full of pesticides? Have we been poisoning ourselves all these years while getting "healthy"? Are mothers killing their children? Or is iron-rich blood more important than poison-free internal organs? Or is the whole a myth perpetuated by the liver-haters? I'm relying on you to give an unbiased answer, even if you're not a liver lover.

Cecil replies:

If you want to know the truth, Alice, I kind of like liver, and always have, although I realize for most people this is akin to saying you have a taste for bondage and discipline. Come on over sometime and we'll split a slab.

You don't have much to fear from liver as far as pesticides go, but there are a few other things in it worth worrying about. Pesticides in general have a fondness for the lipids (fats) and thus tend to wind up in the adipose tissue, or body fat. They can also be found in high concentration in milk, which has a substantial fat content. If you want to avoid pesticides, therefore, stick to lean meat and ice water.

Liver does contain other bad things, though, as do kidneys, whether the beef variety or otherwise. Mostly that's because the two organs play an important role in eliminating toxins from the body. Some of the contaminants can be kept to a minimum through careful management. Government regulations, for instance, require that ranchers wait a specified period after administering certain medications to their livestock before shipping them to market, in order to give the drugs time to be metabolized and/or excreted.

But other toxins are harder to control. In 1980, for example, the Canadian federal health and welfare department found traces of certain forms of dioxin, one of the most poisonous substances known, in chicken livers from a town in Ontario. Dioxin is produced in the course of a number of common industrial processes and can get into the food chain by many routes; the source in the Ontario case was poultry bedding that had been treated with pentachlorophenol (PCP), a preservative in which dioxins are often found. Officials claimed the chicken livers posed no health hazard, but the fact is little is known about what effect minute amounts of dioxin might have on humans over long periods. A study published by two Michigan State University researchers in 1980 indicated that some forms of dioxin tended to concentrate in beef liver, although cooking reduced the level a good deal. The study warned that careless use of PCP on farms could make beef liver dangerous.

Still, for the most part dioxin is a potential problem rather than a current threat. A more pressing issue is the high concentration of trace metals often found in liver and kidneys. Some trace metals, notably iron, are good for you, but others, such as lead, mercury, and cadmium, are poisonous. Cadmium in particular is worth watching out for. The World Health Organization recommends a maximum daily intake of 70 micrograms; the typical daily intake in the U.S. and Canada is 50 to 100 micrograms. The concentration of cadmium in beef liver is two and a half times that in beef muscle tissue, and in kidneys nearly seven times as high. Accordingly, some researchers have suggested the two foods be avoided. While you're at it, you may as well knock off the oysters, too (no problem for Cecil, frankly), which have the highest concentration of cadmium of any commonly available food, some 35 to 50 times the concentration in beef muscle tissue. So if you like liver, be careful. If you eat it only because mom makes you, now you've got an excuse.

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