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Conventional wisdom demands skepticism. Whether it’s the official stance on high-fat diets (“they’ll give you heart disease, don’t work, or do work but not for long!”), exercise (“you must jog at a moderate pace for an hour a day, four days a week!”), organic food (“it’s nutritionally identical to conventionally-grown food!”), or sun exposure (“you must always wear sunblock!”), I always question conventional wisdom. And when it’s lacking (as is often the case), I rightly skewer it.

I’m going to do something a little different today. I’m going to look critically at conventional wisdom, but of a different sort: the kind espoused by the alternative health crowd.

Now, I’m usually sympathetic to them. We align in many ways, perhaps more often than not. We both prefer organic food, wild seafood, and sustainably-raised livestock. We both understand the benefits of smart sun exposure, spending time in nature, and getting ample amounts of sleep. But when it comes to conventional alternative wisdom regarding genetic modification of food — that it makes food unsafe and unhealthy — I have to put on my skeptic’s hat and take a closer look. This is what I do. And don’t worry; in doing so, I’ll also explore the flip side — that GMOs are absolutely, perfectly safe.

I’ve talked GMO before, but the subject hasn’t gone away. If anything, it’s even more prominent a topic of discussion, with articulate salvos fired from both sides of the argument in recent weeks. Today, I’m going to wade in. I can’t promise a final word on all GMOs for all time. I can promise a balanced, level-headed approach to a very testy topic.

So let’s examine some of the arguments commonly provided by people worried about the health effects of GMO foods.

“They’re not safe.”

Well, which ones aren’t safe? GMO is a broad category.

“Bt corn isn’t safe.”

Bt corn is a GMO with a gene insertion coding for production of a bacterial toxin that targets insects. However, this isn’t a novel toxin. The bacteria that produces it — Bacillus thuringiensis — wasn’t created in a lab, and it’s even used by organic farmers as an effective insecticide.

Okay, but Bt toxin applied in powder or spray form can theoretically be removed with washing or processing. If GMO Bt corn has it baked into the DNA, we can’t avoid it. Isn’t that bad for us? After all, Bt toxin is designed to rupture the guts of the insects it targets, and we’re always emphasizing the importance of a healthy, intact gut lining.

Bt toxin is only activated in alkaline digestive systems. Human and other mammalian guts are acidic and thus resistant, while insect guts are alkaline and thus susceptible. And not even every insect seems to be susceptible; bee foraging behavior appears to be unaffected by Bt corn pollen (PDF) and bees with no exposure to Bt corn still show up with Bt toxins in their guts because the bacteria producing the toxin is so common in nature. Bacteria also appear to be unaffected by Bt toxin, indicating a lack of danger to our gut bacteria.

The specificity of action and lack of effect on mammals or non-target microorganisms (soil/gut bacteria) that made Bt toxin so attractive to organic farmers as an external insecticide makes it non-problematic for me as a genetic modification.

“But a Canadian study found Bt toxins in the blood of pregnant and non-pregnant women.”

Here’s the paper. There are serious doubts about the validity of the levels and the tests used to measure them. Plus, since organic farming uses Bt toxin and given the lack of food intake data, we don’t know the actual source of the Bt in the serum. It could have been organic produce. It could have indeed been Bt corn. Even then, there’s still no evidence that Bt toxin is harmful to mammals with acidic guts, so I’m not sure it’s all that relevant.

However, that study did make an important finding: there were also elevated levels of two herbicides associated with GMO foods (glyphosate/Roundup and glufosinate) and their metabolites in the serum. Suspiciously, the article I linked right above skewering the Bt toxin data are silent on the glyphosate and glufosinate (another herbicide) data. They mention it but don’t elaborate. Another similar article from a pro-GMO site also fails to address the herbicide data, claiming the “post is long enough.”

“They increase the use of pesticides.”

The pro-GMO side says GMOs allow reduced use of pesticides, while the anti-GMO side says GMOs allow increased use. Who’s right?

It depends on how you define “pesticides.” If you’re talking insecticides, GMOs generally reduce the use. Bt corn is one example of a GMO crop engineered to express intrinsic insecticidal toxins, thus reducing the amount of external insecticides applied. If you’re talking herbicides, GMOs increase the use.

Overall, GMOs have led to a net increase in pesticide usage (herbicides and insecticides combined), primarily thanks to Roundup-Ready crops. Whether it’s Roundup-Ready beets, corn, soybeans, canola, or even cotton, many GMOs are engineered to thrive despite heavy and frequent application of the herbicide Roundup.

In non-resistant conventional crops, Roundup is applied very carefully:

  • At planting before the crop has emerged.
  • After emergence, avoiding direct contact with the crop.
  • Right before harvest, when the plants are hardy and mature enough to resist it.
  • After harvest, to clear the fields.

When a crop is Roundup-Ready, the herbicide can be applied continuously and indiscriminately without harming the crop. The result is often persistent accumulation of the herbicide in treated foods, as with GMO soybeans.

“Roundup isn’t safe.”

Proponents of GM technology will offhandedly mention the benignity of glyphosate, the active ingredient in Roundup. Even Charles Benbrook, a GMO critic who authored the study showing that GMOs increase pesticide usage and a letter showing the benefits to organic farming, considers it one of the safest herbicides available.

But there’s a small problem with extolling the safety of glyphosate: Roundup isn’t just glyphosate. The herbicide formula contains surfactants and other “inert” ingredients that make glyphosate better at killing weeds and, maybe, causing collateral damage. In one piece of in vitro research, scientists showed that Roundup could be up to 125 times more toxic than glyphosate to human mitochondria. Detractors will cry that the author of that paper, Seralini, is a known anti-GMO activist with serious methodological problems in his other papers (poor controls, small sample sizes, tumor-prone mouse strains). That’s probably fair. He’s not the only one, though. Earlier papers have found similar discrepancies between the effects of glyphosate and Roundup:

Those studies aren’t evidence that Roundup is harming us, but they do show that studies using isolated glyphosate don’t give the whole picture.

“Roundup damages gut bacteria.”

Roundup kills weeds by disrupting the shikimate pathway (PDF), a pathway involved in the biosynthesis of several crucial amino acids. Human cells are relatively unaffected by the herbicide because our cells don’t use the shikimate pathway. There’s nothing to disrupt. All good?

Bacteria also employ the shikimate pathway, and we’ve got an awful lot of them living inside our bodies and handling some very important tasks, including immune function, digestion, production of neurotransmitters, mood regulation, and many more. This means our gut bacteria may be susceptible to Roundup residue on the foods we eat (and the air we breathe, the water we drink, and so on). This isn’t a big issue for people eating primally because the biggest offenders are Roundup-Ready soybeans and corn (and all the related food products) – two foods you likely aren’t eating regularly, if at all. That said, your exposure may be elevated if the food you eat eats a lot of Roundup-laden soy and corn (PDF), like CAFO livestock, dairy, and battery-farmed poultry, all of which may show traces of glyphosate.

Interestingly, a recent paper showed that those very same bacterial species that are reduced in celiac disease – lactobacillus, enterococcus, and bifidobacterium – are the ones most susceptible to glyphosate, while the pathogenic bacteria like salmonella and clostridium botulinium (responsible for botulism) are highly resistant to glyphosate (PDF). Furthermore, glyphosate also inhibits the anti-pathogenic activity of enterococcus bacteria. One of the reasons why “beneficial bacteria” are so beneficial is that they tend to keep the pathogens at bay, and glyphosate directly interferes with it.

“Genetic engineering is different from traditional breeding.”

Yes and no.

In nature, mutations to genes begin at the local level. Genes mutate, creating new alleles, and if those mutations confer survival benefits, the organism possessing them may pass the mutated alleles on to its offspring and, eventually, the species. Traditional cross-breeding co-opts this process, speeds it up, and isolates it, but at the core it’s essentially the same thing. If cross-breeding or natural evolution creates a trait dangerous to humans, we’ll often adapt to it, develop ways to mitigate its harm, or discontinue its use. Either way, the damage is contained to the area of adoption — which for thousands of years of agriculture was relatively small in scope.

Genetic modification in the lab allows instant adoption of new mutations. Once the seeds have been approved for commercial use, they are dispersed to any farm that can afford them. Within a few years, people all over the world are consuming foods that include the new mutation. If that mutation poses a threat to human health or the environment, it becomes a global threat because the scale and speed of laboratory genetic modification is many times larger than that of a naturally-occurring mutation. Traditional forms of genetic engineering (selective breeding of plants to amplify desired traits) begin locally and develop over many generations, giving the environment and its inhabitants plenty of time to adapt to the new mutation or stamp it out. Natural evolution proceeds over an even-longer timescale on the order of hundreds and thousands of years. In the case of GMOs, once the seeds have been approved for commercial use, mutations are global and instantaneous.

I haven’t seen any strong evidence that existing GMO foods introduce traits that are directly dangerous to humans, but the potential exists. If a GMO is going to be problematic over the long term, and these problems aren’t acute enough to show up in safety studies, there might not be enough time for us to adapt.

“Inserting one gene can affect multiple traits, not just the target trait.”

The common misconception about genes is that a single gene affects a single trait. In reality, multiple genes can determine single traits, and single genes can affect multiple traits. Pleiotropy is when a single gene affects more than one seemingly unrelated trait.

Of course, this also holds true for traditional selective breeding. Breeding tomatoes to be sweeter might alter other traits dependent on the “sweetness gene.” And theoretically, genetic engineering should allow greater control over unwanted pleiotropic effects, while selective breeding is more of a shotgun approach with more chances for unwanted pleiotropic effects.

“We need long-term human studies.”

I agree. Unfortunately, we can’t have human studies the way we can with mice. We can’t (and wouldn’t want to, of course) wean babies onto 35% GM soybean diets, track them for several decades, “sacrifice” them, and dissect their internal organs for evidence of pathology.

“I went GMO-free and feel better than ever!”

Say your average relatively uninformed consumer hears about GMO dangers, decides to go on a GMO-free diet, and Googles “gmo free diet.” What does the first result tell them to do?

1. Go organic.

2. Load up on fruits and veggies.

There you have it: going on a GMO-free diet works, for the vast majority of people, because it promotes consumption of organic food, including meat, dairy, fruits and vegetables (which we know are higher in phytonutrients and lower in pesticide residues). It’s not an even exchange for GMO-free versions of common GMO-replete foods. A GMO-free diet almost always works out to be an overall healthier and vastly different pattern of eating that ends up looking a lot like the Primal Blueprint.

“So you’re saying GMOs are safe?”

Not exactly.

I worry about the world’s food supply being controlled by a single company, or an oligarchy of companies.

I worry about the Roundup-Ready gene allows farmers to spray willy nilly. I worry about it ending up in my food and, ultimately, my body. More than anything, I worry about the effect it might have on my gut bacteria.

I worry about the scale and speed at which genetic modifications can be adopted across the globe and hope current testing protocols are sufficient to catch any dangerous ones.

But I don’t see any major issues with the process of genetic engineering in and of itself.

Don’t get me wrong: I avoid GMO foods when I can. But not because I fear genetic engineering. Genetic engineering has the potential to do some really cool things, provided we get it right, like the folks who made low-PUFA, high-MUFA soybean oil.  I avoid GMOs because I don’t want to consume Roundup, which as far as I can tell likely causes most of the problems linked to GMO foods. Because I don’t eat very much corn, soy (except for natto, and the only natto I’ve found without junk in the ingredients uses organic soybeans), sugar beet (I much prefer organic beets from the farmer’s market with the greens still attached; if you’ve never had beet greens, sauté them up in olive oil with some garlic and serrano chiles for an arguably superior alternative to spinach and kale), canola oil, or cotton (tastes terrible).

Oppose specific GMO foods. Explain why you don’t want Roundup-Ready beets and soybeans in your diet — because the Roundup it allows farmers to apply in ever-increasing amounts isn’t benign. Don’t rail against all GMOs because of something you don’t like in one. Don’t be like the skeptics who deride all organic foods because a study they like found identical levels of vitamin C in conventional and organic strawberries.

Genetic engineering isn’t inherently harmful to human health. It’s weird. It’s new. And putting a bacterial gene in your carrot or whatever sounds crazy, but it’s not necessarily bad.

What do you think, everyone?

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