Are GMOs bad for your health? Here’s what the science says

Should I worry about GMOs? Are they bad for my health?

GMOs, or genetically-modified organisms, have been swept into the larger conversation about chemicals, antibiotics and additives in our food supply. But there’s nothing inherently unsafe about genetically modified crops. What should give you pause, instead, is the potential risk of herbicide exposure — which can be an indirect result of modern GMO farming.

The most commonly grown GMO crops in the United States are soy and corn that are resistant to the herbicide glyphosate, which the International Agency for Research on Cancer has labeled a probable human carcinogen.

Several studies have shown that consuming GMOs is not associated with elevated health risks, including cancer. But glyphosate use has risen dramatically in the United States since the 1990s, and we lack long-term epidemiological data about what this may — or may not — mean for our health. There is also some emerging data regarding glyphosate exposure, especially among younger children, worth considering.

As we take into account what we do know, here’s my advice: GMOs are likely fine for adults to consume, especially if you minimize ultra-processed foods, which are generally linked to adverse health outcomes and are a common source of GMO corn and soy. For pregnant women and young children, it would be very reasonable to minimize consuming GMOs and ultra-processed foods whenever possible.

What are GMOs?

A GMO is an organism, such as a crop, whose genes have been selected for a superior trait. A GMO is not a modern concept. Farmers have been selectively breeding plants chosen for desired traits for thousands of years. The entire field of Mendelian genetics was born from experiments crossbreeding peas to learn about gene inheritance.

For instance, have you ever found it odd that an eggplant, that large deep-purple blob, was named for an egg? It was selectively bred this way. The common eggplants of centuries ago were actually more like small white ovals.

Of course, our modern techniques are very different: GMOs may undergo an accelerated process of gene engineering in a laboratory to insert a new gene from another organism into the DNA. Today, the most common traits that have been widely selected in GMOs are tolerance to herbicides and insect resistance.

With these GMOs, rather than having to rely heavily on mechanical weeding, farmers have used increasingly larger amounts of herbicides that don’t harm their crops. As a result, measurable quantities of herbicides like glyphosate have been detected in GMO grains intended for our food, animal feeds and in some areas’ drinking water.

What are the health risks with GMOs?

Human studies that have linked glyphosate to cancers like Hodgkin’s lymphoma predominantly evaluated farmers with high levels of occupational exposure, not people exposed via GMO consumption in daily life.

The National Academies of Medicine reviewed over 900 studies in 2016 on GMOs and did not find any evidence of elevated health risks, including cancer. But to be clear, that report (which is now almost 10 years old) acknowledged that we lack long-term epidemiological data about the indirect exposure to herbicides possibly associated with GMOs.

Reassuringly, in 2021, the USDA conducted a study of over 10,000 randomly sampled foods across the country and found that more than 99 percent contained pesticide levels well below the safety thresholds set by the Environmental Protection Agency.

Why are children more at risk?

The evidence gets more complex for children, who are more developmentally vulnerable to toxins and stress. A large retrospective study published this January in the Proceedings of the National Academy of Sciences (PNAS) looked at U.S. rural birth records between 1990 and 2013. Researchers from the University of Oregon found that babies with higher glyphosate exposure, particularly in the rural South and Midwest, were more likely to be born with lower birth weights — a change that they found occurred around the rollout of GMOs after accounting for confounders like use of other pesticides, local income, employment rates and demographics.

The prospective studies are small and limited, but the findings still warrant pause: A 2021 study of 250 pregnant women in Puerto Rico — the largest study of its kind — found that prenatal exposure to glyphosate (measured objectively in urine samples) was associated with a 35 percent increased odds of preterm birth.

What crops are allowed to be GMO?

GMOs are not as ubiquitous as many think. There are only 11 approved GMO crops grown in the United States, including apples, potatoes and papaya. The list does not include crops like tomatoes, wheat and strawberries, for example. You can check out the full list here.

Rarely, and under tight regulations, a new GMO enters the market: Last year for the first time a genetically engineered banana was approved in Australia and New Zealand to combat fungal disease.

How do I know if a food has GMOs?

To easily identify whether foods are GMOs, look for a non-GMO or organic label. Organic foods are defined, according to the USDA, by avoidance of synthetic pesticides, fertilizers, antibiotics and other farming practices like genetic modification.

It bears noting that for the most part in the United States, there are no inherent nutritional differences between GMOs and their organic counterparts. Most people cannot distinguish GMOs in taste, and there have been a paucity of studies that have ever demonstrated a meaningful personal health benefit of organic foods among adults.

What I want my patients to know

The 2021 study from the USDA washed much of its fresh produce as part of standard procedures before testing. If you wash any fresh GMO produce before consumption, which many people do anyway, you’ll minimize (though perhaps not entirely eliminate), the risk of exposure to pesticides.