Only one movement has science to back it.

Poultry giant Foster Farms announced this week it would cut back on the antibiotics it feeds to its chickens. This follows similar promises from Tyson Foods and Pilgrim's Pride, the top two poultry processors in the United States. (Foster Farms is number 10.) Meanwhile, restaurants such as McDonald's and Chick-fil-A have pledged to serve McNuggets and Chick-n-Strips made from chickens fed fewer antibiotics.

It's a veritable trend! In fact, it reminds us of another trend—the one against GMO foods. Chipotle became emblematic of that movement last month, when it promised it would go GMO-free, a first for a restaurant chain. But there's one major difference between the movement against agricultural antibiotics and the one against GMOs: There's much more science to back the former, making the latter look like little more than a PR move. As NPR's "The Salt" recently noted, Chipotle is trying to have its cake and eat it, too: It won't officially acknowledge that GMOs are unhealthy to eat, yet its website seems pretty clear on wanting to stoke consumers' fears.

But we're not here to debate the marketing tactics of Mexican-ish chain restaurants. We're here to talk about the science. Let's take a look.


The problem with feeding animals antibiotics is that the over-use of those medicines makes them less effective in treating not just animals, but sick people, too. Giving a limited number of sick animals antibiotics when they need them is not too controversial. However, some farmers regularly feed low doses of antibiotics to large numbers of their livestock and poultry, sometimes to prevent illness and sometimes because, strangely enough, taking constant low doses of antibiotics makes farm animals gain weight. These practices create the perfect conditions for super-antibiotic-resistant bacteria to evolve. Studies have shown these bacteria are able to then make their way out into the environment, and eventually to human beings. And we're not talking about some small-scale incident: Antibiotic-resistant illnesses kill 23,000 Americans a year, according to a 2013 estimate by the Centers for Disease Control and Prevention. Not all of these illnesses are a result of farm practices, but there's scientific evidence that at least some are.

Studies back each of the pieces of logic that fit into the argument against the excessive use of antibiotics on farms.

It's a relatively new idea, this notion that antibiotics used on farms reduce the effectiveness of medicines in hospitals. Yet there are studies that support it every step of the way. It's well-documented that microbes infecting both people and farm animals are able to develop antibiotic resistance in response to drugs. There are many reasons this resistance arises. Recent studies show that antibiotic use on farms is one important explanation, as resistant bacteria are more common on farms that use more of the drugs.

There's emerging evidence that these resistant microbes can end up in people far away from farms. (Farm workers, of course, are at particular risk.) Certain antibiotic-resistant genes appear in both farm animals and people, suggesting they have a common origin.

But how did those genes arrive in people? Eating contaminated meat may be one route. Researchers have discovered antibiotic-resistant bacterial genes on raw meat sold in stores, and one study found that when people ingest drug-resistant bacteria in meat and milk, those critters persist in their digestive systems for at least 14 days.

Contrast all this to the evidence for the harms of eating genetically modified foods. One recent analysis of peer-reviewed GMO safety tests, including 770 studies that had to do with animal and human health, found that "the scientific research conducted so far has not detected any significant hazards directly connected with the use of GE crops." In 2012, a team of biologists published a popularly cited study, which found that rats eating genetically modified corn grew tumors. However, the journal publishing the study ultimately retracted it, because the researches used too few rats (and of a type that is naturally prone to tumors) to draw strong conclusions.

Another major worry of anti-GMO activists is that those crops genetically modified to resist herbicides—developed so that farmers can spray their crops indiscriminately, without killing their corn and soy plants—might lead to the evolution of super-weeds. This argument rests on biology that's similar to the science supporting the reduction of antibiotics on farms. And it's true. Since the introduction of Monsanto's Roundup Ready technology, farmers use much more of the Roundup herbicide, called glyphosate, than they did before. In response, weeds have quickly developed their own resistance. Agricultural researcher Bryan Young of Southern Illinois University links Roundup Ready technology to a decline in other, perhaps healthier weed-control methods, such as tilling.

It's important to know which policies are worth supporting and fact-checking over time—and which are little more than advertising masquerading as science.

Yet it's not genetic modification, exactly, that created this problem. It's Roundup Ready-type technology in particular. Opposing GMOs because of the consequences of Roundup Ready misses the point and creates problems for other genetically modified crops that may be helpful to communities, like vitamin-enriched crops. Those interested in opposing the over-use of herbicides should focus on that—and keep in mind that plenty of unmodified crops also rely on heavy herbicide use, such as sunflowers.

This is not to say that Foster Farms and McDonald's have America's best interests at heart. All food producers' public announcements about new policies, whether they're anti-antibiotics or anti-GMOs, are intended to benefit companies' bottom lines. That's business. People care deeply about the perceived safety and health of their foods, and health pledges present an easy hook. But it's important to know which policies are worth supporting and fact-checking over time—and which are little more than advertising masquerading as science.

Lead photo: Chicken coop. (Photo: branislavpudar/Shutterstock)