Two events in the past few months raised the profile of foods with genetically modified ingredients – and also put a spotlight on how messy the issue can be.

The first was the publication in September of a study led by Gilles Eric Séralini involving the herbicide Roundup and herbicide-resistant Roundup Ready corn (technically known as NK603) – both Monsanto products. Rats in the study developed tumors, died prematurely, and suffered organ damage.

The second was the defeat in November of California Proposition 37, whose ballot summary read that it would have required the “labeling of food sold to consumers made from plants or animals with genetic material changed in specified ways.”

There was a lot of heat with both events.

The Séralini study and its PR roll-out were met with an intense backlash from genetic-engineering apologists and much of the scientific community, and the European Food Safety Authority – among other scientific organizations – rejected its validity, saying it featured “inadequate design, analysis, and reporting.”

In California, Prop 37 opponents – including Monsanto Company, E.I. DuPont de Nemours & Company, and the Grocery Manufacturers Association – spent more than $40 million to defeat the labeling ballot measure.

Yet combined and detached from the rhetoric and motivations on all sides, these two events neatly summarized the national and international debate over foods with genetically modified ingredients. Are they safe for human consumption? And should the government require the labeling of foods with genetically modified ingredients – the way nutrition and ingredient labels now note the presence of allergens?

Depending on whom you ask, the answer to the first question ranges from “absolutely” to “we don’t know” to “absolutely not.” And the answer to the second question is largely – but not wholly – determined by the answer to the first.

In addition to California’s failed proposition (which lost 52 percent to 48), efforts are underway nationally and in many states to mandate the labeling of food with genetically modified ingredients. More than four dozen countries presently require these labels, but the United States does not.

The Just Label It (JustLabelIt.org) campaign says more than 1.1 million people signed its petition to the Food & Drug Administration (FDA) asking the agency to label foods with genetically modified ingredients. “We really believe this is an honesty, transparency, and good-business practice that we really need to shed light on what’s in America’s food,” said Executive Director David Bancroft.

In Iowa and Illinois, Food & Water Watch is pushing for state action on labeling.

Surveys regularly show that a vast majority of respondents favor mandatory labeling, although opponents of labeling claim those figures are inflated by leading questions and incomplete information. They cite the California vote as an example of how support softens when other factors – such as their claims of higher food costs associated with mandatory labeling – are thrown in. (They fail to note, of course, the impact of tens of millions of dollars in food-industry campaign spending against the ballot measure, and as with most political advertisements, truth and fair context were hard to find in California.)

It’s a complicated, nuanced issue with safety, cost, environmental, regulatory, political, ethical, and scientific elements, and that’s exacerbated by the spin and noise on all sides. Still, focusing on those two core questions of safety and labeling can cut through a lot of that.

What Are GMO Foods?

You’ll see a lot of different terms describing the same thing as it relates to food: GE (genetically engineered), GM (genetically modified), GMO (genetically modified organisms), and biotech. You’ve also probably come across the vivid and derisive “Frankenfoods.”

With all of these, we’re talking about the insertion into one organism of a gene from another organism. If the species are not related, this is called “transgenesis”; if the species are closely related, it’s called “cisgenesis” or “intragenesis.” To give an extreme example of this concept, transgenesis has been used to create goats with a spider gene that makes them produce milk with spider-silk proteins.

While transgenesis and cisgenesis are clearly different from traditional agricultural “selective breeding” – for example, the breeding of two corn varieties to produce a third – their goals are the same: to create a new product that is in some way superior to what was previously available.

In 1994, the Flavr Savr tomato became the first GMO approved for marketing in the United States. This variety delayed ripening, which meant that it would stay fresher longer.

In theory, genetic engineering can be used to create all sorts of favorable food characteristics – from greater shelf life to higher yields to improved nutritional content. In a food context, genetic engineering has produced golden rice, which through the addition of genes from a daffodil and a bacterium increased levels of beta-carotene; the product was developed to combat Vitamin A deficiency – an example of how genetic engineering might be used to address global food and nutrition needs.

But the most common deployment of GE crops is in the battle against weeds and insects. Roundup Ready crops from Monsanto, for example, are resistant to the company’s Roundup herbicide. And many crops have been engineered to produce their own insecticide – Bt derived from the bacterium Bacillus thuringiensis. So the question of food safety must also consider the health effects of the chemicals used to protect some GE crops and the pesticides produced by others.

According to the International Service for the Acquisition of Agri-Biotech Applications, in 2011 the United States dedicated more than 170-million acres to biotech crops – tops in the world – including corn, soybean, cotton, canola, sugar beet, alfalfa, papaya, and squash.

Worldwide, it said, herbicide resistance is the most common biotech trait, present in 59 percent of nearly 400-million GE acres. Crops with multiple biotech traits covered 26 percent, and insect resistance covered 15 percent.

The organization said that 29 countries have planted commercialized biotech products, and another 31 countries allow biotech crops to be imported for food and animal-feed use. Genetically engineered varieties of 25 crops – from corn to potatoes to tobacco to roses – have been approved by national governments for commercial cultivation or use as food or feed.

Widely cited figures suggest that GMOs are present in the ingredients of between 60 and 80 percent of foods in United States grocery stores – although those numbers are almost certainly rough estimates and largely meaningless without more details and definitions. But it’s safe to say that because of the prevalence of corn, soy, vegetable-oil, and sugar inputs in processed food, you’d be hard-pressed to avoid them without some sort of GMO labeling – whether a positive statement of their presence or a negative statement of their absence.