GMO ingredients have never been adequately tested for long-term impacts on public health despite hitting the market in 1996. There are about 600 studies focusing on the composition of genetically engineered foods, looking at things like calories, protein, fat, and vitamins. These mostly industry-funded studies are generally performed to show the Food and Drug Administration that the food is nutritionally comparable to non-GE foods, or to convince livestock farmers that GE feed is on par with non-GE feed. Both types of studies have next-to-nothing to do with human health and safety, Benbrook warns.
Some of the very few studies looking at shorter-term health impacts suggest cause for concern. A carefully designed meta-analaysis of 19 longer-term published studies looking at mammals found those fed genetically engineered corn or soybeans experienced kidney, liver, and bone marrow damage, potential indicators for chronic disease. GMOs are also implicated in skyrocketing food allergies rates and Roundup, the chemical often sprayed on GMOs, has been linked to certain cancers, DNA damage, premature births, and ADHD. Warren Porter, PhD, professor of environmental toxicity and zoology at the University of Wisconsin, Madison, analyzed government data on glyphosate in the environment and found cause for concern. The levels could lead to accumulated levels that could alter endocrine-mediated pathways, leading to obesity, heart problems, circulation issues, and diabetes, as well as lead to low level glyphosate levels have also been linked to immune system damage, birth defects, cell death, and learning disabilities.
It's not good for animals, either. In a recent study published in the Journal of Organic Systems, Australian and U.S. researchers found pigs fed genetically engineered feed were much more likely to suffer from severe stomach inflammation and heavier uteri, a condition that could signal endometrial cancer, endometriosis, abnormal thickening, or gynecological polyps—all things that could affect fertility.