There are toxicological issues associated with production and processing of meat, such as the presence of various toxic contaminants—from dioxins and PCBs to cooked meat carcinogens. Carcinogenesis, the development of cancer, may be the main concern, but there are a number of other toxic responses connected with the consumption of meat products. Lead, for example, can be toxic to the nerves, gastrointestinal tract, bone marrow, and kidneys.

Where is lead found in the food supply? In general terms, the highest levels of lead, as well as arsenic and mercury, are found in fish. Sardines have the most arsenic, but tuna may have sardines beat when it comes to mercury and lead.

The problem is that “fish-consumption advisories related to human health protection do not consider the fish by-products fed to farmed animals,” like farmed fish. If some tilapia are fed tuna by-products, they could bioaccumulate heavy metals and pass them onto us when we eat them. Researchers found the highest levels in frozen sole fillets, averaging above the legal limit for lead.

Lead exposure has been shown to have adverse effects on nearly every organ system in the body. Symptoms of chronic exposure range from memory loss and constipation to impotence and depression. These symptoms present after pretty hefty exposure, though. However, we now know that “[b]lood lead levels in the range currently considered acceptable are associated with increased prevalence of gout and hyperuricemia” (elevated levels of uric acid in the blood). According to the Centers for Disease Control and the World Health Organization, a blood lead level needs to be less than 25 micrograms per deciliter to be “non-elevated.” You’d assume that at values under 25, there’d be no relationship with health outcomes, but even throughout this “acceptable” range, lower lead means lower uric acid levels and lower gout risk. So, even blood lead levels 20 times below the acceptable level can be associated with increased prevalence of gout. “These data suggest that there is no such thing as a ‘safe’ level of exposure to lead.”

Once lead gets into the body, it tends to stay in the body. It builds up in the bones such that it may take 30 years just to get rid of half. The best strategy? Don’t get exposed in the first place.

If lead builds up in bones, though, what about boiling bones for broth? As I discuss in my video Lead Contamination in Bone Broth, we know bones sequester lead, which can then leach from the bones. So, researchers suggested that “the bones of farmyard animals will sequester lead, some of which will then be released into broth during its preparation.” Who eats bone broth? Bone broth consumption is encouraged by many advocates of the paleo diet. Online, you can learn all about purported “benefits” of bone broth, but what they don’t tend to mention is the theoretical risk of lead contamination—or at least it was theoretical until now. Broth made from chicken bones was found to have markedly high lead concentrations, up to a ten-fold increase in lead. Researchers concluded, “In view of the dangers of lead consumption to the human body, we recommend that doctors and nutritionists take the risk of lead contamination into consideration when advising patients about bone broth diets.”

But what if you only use bones from organic, free-range chickens? They did use only bones from organic, free-range chickens.

For more on the paleo diet, see:

Other products contaminated with lead include Ayurvedic supplements, protein powders, wild animals shot with lead ammunition, dairy products, and tea from China:

In health,

Michael Greger, M.D.