Ideally, The Primal Blueprint is a living, breathing document. Whether it’s emails from insightful readers or random articles from my RSS feed casting a subject in a completely different light, or even personal N=1 revelations spurring a meticulous re-examination of previously-held stances, I’ll often find myself rethinking certain aspects of the PB. They usually hold up pretty well, mind you, but it’s always good to take stock of the evidence. It keeps us in the Primal community on our toes. Take yesterday’s post, for example. The discovery of grain residue from a 100,000 year old dig site was undoubtedly intriguing, because it suggested that a major tenet of the Primal lifestyle – that grains have no place in the human diet – might need some refining. In the end, our position remained the same (the intense labor inherent in the sourcing, gathering, hulling, processing, and cooking of grass seeds would have been too great for Grok to make it a staple food – especially when nutritionally-superior and far more nutrient-dense alternatives existed in abundance), but it was tested and therefore strengthened.
Sometimes, though, new evidence forces me to completely rethink things. Even something so seemingly innocuous as a random comment from a reader can set me off on a researching bender. Last week, someone mentioned the Bisphenol A (BPA) leaching tendencies of canned tomatoes. That was all it took to send me on a tear.
First, I looked deeper into the BPA issue. I’ve mentioned it before, and the battles over BPA content in plastics have gotten a lot of publicity, but after looking at the preponderance of evidence derived from recent animal trials, I’m not sure I can recommend using canned food at all anymore. Industry leaders say BPA is crucial for preventing direct contact between food and metal; they also say ditching the stuff would lead to far more botulism cases. That may be. But it’s undeniable that BPA has an effect on animals. Various dosages have different effects, and it’s unclear whether the animal models are relevant to human models, but the stuff does leach and it does impact the mammals that have been tested. A quick rundown (these are rodent studies unless otherwise noted) of dosages in µg/kg/day and the reported effects:
0.025 – Permanent changes to genital tracts in adult females with in utero exposure to BPA that only show up during adulthood. This may be attributed to “increased expression of estrogen receptor-alpha and progesterone receptors.” Another study found that BPA exposure “increased terminal end bud density at puberty as well as… terminal ends… in adult animals” in the mammary glands. In both rodents and humans, the end and terminal buds are where cancer arises.
1.0 – Ovarian cysts were seen in adult mice with prenatal exposure to BPA, but not in the corn oil group (don’t go chugging corn oil, though!). BPA-treated mice also exclusively displayed other adverse reproductive and carcinogenic effects, including sarcoma of the uterine cervix (a fairly rare cancer) and mammary adenocarcinoma (breast tumor).
2.0 – Pregnant mice fed normal levels of (read: in doses similar to the range “currently being consumed by people”) BPA, but not octylphenol (another xenoestrogen used in commercial products), bore males that developed enlarged prostates by adulthood.
2.5 – Given no further “treatment aimed at increasing tumor development” beyond fetal BPA administration, mice mammary glands were induced to develop carcinoma. Mice with prenatal exposure, then, were predisposed to breast cancer in adulthood.
50.0 (the official U.S. human exposure limit, as ordained by the EPA) – In nonhuman primates, continuous administration of BPA interfered in the formation of spine synapses in the hippocampus and prefrontal cortex. Spine synapse formation is especially critical in the regulation of mood and general cognition; government-approved levels of BPA were enough to “abolish” synapse formation in some of our closest primate relatives.
There are plenty more, too.
(You might be wondering whether injecting rats with BPA is relevant to the kind of environmental exposure we humans get. Scientists found that the route of BPA administration in these studies – whether BPA was injected or given orally – did not impact plasma levels of the xenoestrogen. No matter how small the dose, oral exposure and injection resulted in identical blood plasma levels – so don’t think that just because we’re not shooting up with syringes of BPA we’re necessarily avoiding enhanced blood plasma levels.)
What makes these intriguing (and somewhat worrisome) is that dosages were kept well within the official daily limit supposedly tolerated by humans. In fact, most of the dosages fell far below the daily limit set by the EPA: 50 µg/kg/day.
Then I got to wondering just how much BPA we’re exposed to on a regular basis. While this PDF table, courtesy of Consumer Reports, may not apply to most of our readers, it gives a good idea of the amount of daily BPA regular folks who eat processed, canned food on a regular basis are taking in. If, for example, you eat a serving of Progresso Vegetable Soup, you’re eating (on average) 22 µg of BPA. A serving from a can of Del Monte Fresh Cut Green Beans contains 14.9 µg. A serving from a can of Campbell Chicken Noodle Soup contains 10.2 µg. These are just servings, mind you, and how many people just eat a third of a can of soup or green beans?
But wait – 22 µg, 14.9 µg, 10.2 µg? That doesn’t sound like much. Besides, the EPA and FDA say 50 µg/kg/day is totally safe. What’s to worry about?
Well, Consumer Reports also employs its own food safety experts. The same ones who ran the test on the BPA levels of popular packaged items arrived at a slightly different safe daily dosage, believe it or not. Citing the fact that exposures of 2.4 micrograms of BPA per kilogram of body weight resulted in reproductive and sex hormone issues in rats (see above), the Consumer Reports food safety scientists “recommend 0.0024 micrograms per kilogram of body weight.” That means just a single serving of Del Monte green beans would put a 165-lb adult about 80 times past the Consumer Reports daily limit. Is that too much? Whom should we listen to – the FDA or Consumer Reports?
According to BPA researcher Frederik vom Saal, professor of developmental biology at the University of Missouri at Columbia, most regulatory standards regarding industrial chemicals are based on tests of abnormally high doses, but the evidence clearly shows that seemingly minute doses can have “completely different and potentially more harmful effects.” The FDA’s dosage limits, then, seem based on faulty or incomplete evidence. Even a special FDA scientific advisory panel was critical of the official company line, expressing disagreement with the FDA’s dismissal of a “large number” of studies on BPA. Congressmen Henry Waxman and Bart Stupak echoed the calls for further review of the official stance on BPA in a recent letter to the FDA commissioner, suggesting that “an industry meeting last week to discuss ways to block restrictions on BPA” indicated a willingness “to mislead the American people on this public health issue.” The two congressmen were of the opinion that the FDA shouldn’t exclude non-industry funded studies from consideration.
I’m not a fan of politicians, but I’m going to have to agree with these two. The evidence that BPA is damaging across a whole range of dosage levels in animal models is pretty compelling and deserves further consideration. It isn’t conclusive, but when we’re talking about the widespread, near-daily ingestion of manmade chemicals that exhibit some classically xenoestrogenic effects, it’s better to err on the side of caution and take a good hard look.
Some have tried. There are some limited human studies on BPA, but they haven’t established anything beyond correlation. In 2008, results on the first major study of health effects on humans were published. Higher serum BPA levels were strongly associated with various disorders, including heart disease and diabetes. Was it the BPA causing the problem, or was BPA merely a marker for processed junk (canned/in plastic) food consumption? Causality cannot be confirmed. Other studies have associated recurrent miscarriage, oxidative stress and inflammation with urinary concentrations of BPA, and another study (PDF) found an association between prenatal exposure to BPA and externalizing behaviors in children, including aggression, delinquency, and hyperactivity. “Altered hormone levels in men” have also been linked to urinary BPA concentrations.
Based on the animal models in which serum BPA had measurable effects, especially on developing fetuses, I think there might be something more than pure correlation going on here. We already know that BPA has been found in umbilical cord blood (PDF), so the possible delivery system is there. We already know that various amounts of BPA show up in canned and processed food, so there’s a possible source that people are tapping into. What we don’t know for sure is whether the dosages are safe or not. Do we trust the FDA or CR?
If a government agency explicitly tasked with regulating the safety of all the various things consumers put into their bodies can’t be bothered to look at the actual studies attempting to establish whether something is safe or not, I’m not sure I want to listen to its daily dosage recommendations. Consumer Reports is generally well-regarded, and they don’t exclude a study simply because its findings were inconvenient. While their donors may have agendas, at least those agendas, as far as I’m aware, don’t revolve around removing restrictions on potentially harmful chemicals.
So, what about the tomatoes – will I be tossing all my cans of organic tomato paste and organic crushed plum tomatoes? Probably not, to be honest. I don’t plan on giving birth anytime soon, and I don’t see myself prematurely entering puberty. I’m also a big fan of chili, which simply isn’t the same made with fresh tomatoes. I am going to look for alternatives, though; I plan on trying canning again, and I might give those glass jar tomatoes from Tropical Traditions a shot. A quick Googling reveals a number of other glass jarred tomato vendors if those don’t work out. I think Whole Foods might even carry a brand, but I can’t be sure. Eden Foods uses BPA-free cans, if you can find them.
Okay, maybe the new “stance” on canned food isn’t so new or revolutionary. We already avoided the stuff simply because it usually meant you weren’t eating fresh, whole food; now we’ve just got another reason to avoid it. Let’s hope more consumers come to the same conclusion, though, because I somehow can’t see the FDA or the industry having a change of heart anytime soon.
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.