We know that eating food derived from genetically modified crops won't make you keel over and die. How do we know that? According to the USDA, about three-quarters of US corn and upwards of percent of soy are from genetically modified seeds—a rapid ascent since their roll-out in the early '90s.
Those two crops suffuse our food system: they provide the sweetener for soft drinks, the cooking oil for French fries, feed for the animals we eat, and countless ingredients used by food processors. By 2003, the Grocery Manufacturers of America was already reckoning that 75 percent of processed food in supermarets contained GMO ingredients. So if eating a bowl of cereal made from GMO corn, or a Pop Tart sweetened with high-fructose GMO corn syrup, posed an immediate threat, or a we'd know it by now. Millions of people do it every day. So for what public-health people call acute effects, GMOs have more or less been proven safe.
But what about chronic effects—slow-moving, unspectacular conditions that could take years to detect, much less to diagnose? Here we're on murkier ground. GMOs have been on the market for less than a generation: not a large span of time for gauging long-term effects on a population.
And to be sure, the US is riddled with chronic health conditions like diabetes, obesity, and heart disese. The CDC reports that one in two Americans now have such conditions, and that seven of every 10 deaths in the US can be attributed to them. According to a 2010 study in the Journal of the American Medical Association (summarized here), the rate of chronic conditions among US children jumped from 12.8 percent in 1994 to 26.6 percent in 2006, with asthma, obesity, and behavior/learning disorders leading the way.
Clearly, such trends are highly complex and can't be explained by any one factor. And the US diet, with its reliance on calorie-dense, additive-laden processed food, went downhill long before the introduction of GMOs in the '90s. But did the introduction GMOs make the whole witches brew of US processed food even worse, and add subtly to its already-bad health effects? To me, it's plausible.