This Research Undercuts the ‘Emotional’ Argument on GMOs

Depending on your worldview, GMOs might be a gastronomic menace. Must be something you ate? We’re conditioned to think there’s something viscerally “off” about them. Overdramatic headlines feed a steady diet of preconceived notions, in turn fueling anti-GMO fervor.

Feed and diet are the operative words here. One of the most persistent myths surrounding GMOs is the supposed long-term harm on our delicate internal landscapes — the “gut” (of microbiome fame) in particular.

Yet a 2025 study is poised to put some of those lingering doubts to rest. This singular study — and I’m normally wary of one-hit wonders — is framed as the unceremonious end of the “emotional era,” a bookend to the remarkable proliferation of nonsensical, dubious, and boldfaced lies swirling around GMO safety in our diets.

The study, published in the peer-reviewed journal of Food and Chemical Toxicology, is titled, A 7-year feed study on the long-term effects of genetically modified maize containing cry1Ab/cry2Aj and EPSPS genes on gut microbiota and metabolite profiles across two generations of cynomolgus macaques.

Historic naysayer claims have been confident, strident, and chronic: They like to argue that GMOs supposedly have uniquely toxic pedigrees, with reverberating effects across generations, in food webs, as well as bioaccumulation a la mercury and other environmental toxicants. Additionally, it’s claimed they’re teratogens (causing birth defects) and/or carcinogens (cancer-inducing). More specifically, GMOs are framed as a biological sterilant of sorts, razing the gut microbiome like a lawnmower run amok.

Real or perceived, these are an ongoing concern with a captive audience. How long have GMO foods been available for consumption? What does the data say — the ultimate fodder and arbiter for risk managers and policymakers alike?

Initially released in 1994 (the Flavr Savr tomato), GMOs have been the most thoroughly studied innovation in the history of humankind, bar none. The literature is robust, and, barring some dubious outliers, the conclusions unequivocal. On the human health front — and after a billion plus meals — GMO foods have caused nary a sniffle.

The vast majority of studies focus on feeding GMO ingredients to model animals. The idea is that they serve as proxies — a best-guess stand-in for the genuine human article. Does a rodent approximate the response a typical human would have to comparable conditions? It’s imperfect, but it’s a start. Organismal (whole organisms, not a petri dish, despite the protestations of the animal rights lobby) are the most suitable approximations.

Additionally, how many of these studies are “long” term? Short-term (acute) studies understandably form an incomplete picture. What criteria are used to define “long term”? Skeptics invariably bring up the question, and it’s a valid one. Long-term (chronic) studies fill in these knowledge gaps, to fully resolve the dynamics.

For testing purposes, 90 days is typically considered adequate. However, the longer the duration, the more exhaustive the dataset, and the greater the confidence in the final conclusion. Even careful statistical analysis can sometimes misconstrue results with a limited dataset. Background noise might be elevated, with meaningful results obscured.

The “study to end all studies” referenced earlier was impeccably intentional in its design on both model animal and duration fronts. It used 1) cynomolgus macaque primates (90%+ DNA sequence similarity to humans, with select regions even higher) and 2) raised the bar with a seven year longitudinal (long-term observation and evaluation of the same cohort) and multigenerational study (two generations, a further refinement to examine potential intergenerational harm and heritability).

The objective was straightforward: assess the impact of GMO corn on immune and metabolic health. Two traits in a “stacked” GMO corn variety were evaluated: insecticidal Bt traits (cry(stal)) proteins that have activity against caterpillars, as well as Roundup Ready (herbicide tolerance) traits.

Data on immunoglobulin profiles, cytokine networks, and serum metabolome parameters were assessed. There were some trivial differences in blood and metabolic parameters, but they were not clinically significant.

The GMO diet also received a clean bill of health regarding chronic inflammation, autoimmune responses, and general toxicity.

This study was not only designed to standard, but leapfrogged it. Multigenerational, longitudinal studies are the gold standard. The likelihood that results deemed significant (or insignificant) are a false flag is appreciably less — though never zero.

Skepticism should be the default state for all scientific pursuits. In science lingo, the classic baseline is the “null hypothesis.” Barring evidence to the contrary, the treatment (consumption of GMO foods) is assumed to be a wash with the non-GMO control. In other words, the burden of evidence rests with careful statistical analysis of the raw data. If measurable effects can be teased out, the null hypothesis is rejected, indicating significance (e.g. GMOs cause effect XYZ).

The irony of selective scrutiny is not lost on scientists. Process- vs. product-based regulation has two very divergent regulatory tracks. GMOs attract (arguably) undue attention — borderline inquisition — simply because of how they were created, not what end product was created. For example, chemical and radiological inducement of mutations is commonplace; the latter was downright fashionable in the nascent years of the atomic era. These methods haphazardly scramble DNA, causing breaks, point mutations, and other anomalies, all for the express goal of “inventing” new breeding diversity.

Similarly, conventional breeding has next to no oversight, save minor instances (like toxins in potatoes). These methods are greenlit with little thought, let alone exhaustive feeding tests over multiple generations. No other method of plant breeding — with tactical precision mind you — is forced to slog through the gauntlet, constantly second-guessing its merits.

In the wake of this primate study, does it make sense to continue to conduct GMO feeding studies? DNA and RNA are considered GRAS (generally recognized as safe), readily digestible with no bodily persistence. Transgenes don’t linger like a circulatory plaque. There’s no expectation of chronic, accumulative effects.

Would human studies placate the naysayers? It would undoubtedly provide the most conclusive evidence — but short of the odd study on protein digestibility and allergenicity — bioethical concerns relegate that to a pipe dream. Why? Testing often necessitates force feeding an inordinate amount to subjects over a defined period of time. I doubt any volunteer would be able to stomach that proposition.

So is the “science settled” on the health effects of GMOs? There’s healthy skepticism — and denialism/obstructionism. The former deserves an audience; the latter a sound rebuke. In the wake of this study attesting to the safety of GMOs in a primate model — the most apt stand-in we can hope for — and an already exhaustive supporting body of literature, it’s time to let biotech flourish.

Tim Durham’s family operates Deer Run Farm — a truck (vegetable) farm on Long Island, New York. As an agvocate, he counters heated rhetoric with sensible facts. Tim has a degree in plant medicine and is an Associate Professor at Ferrum College in Virginia.