With the Nov. 4 ballot measure, Colorado is at the forefront of a fierce food fight raging across the nation: whether or not to label foods made with genetically modified organisms, or GMOs, so consumers can easily see if the food they buy is a product of genetic engineering.

Similar ballot initiatives failed in California and Washington in the past two years.

This spring, Vermont became the first state to approve GMO labeling. But then a group of national organizations — led by the Grocery Manufacturers Association — filed a lawsuit in federal court that challenges the new law. This could be the first of many lawsuits to block mandatory GMO labeling, experts say, and now Colorado jumps into the high-stakes debate.

“It will be a hot issue for quite a while in this state,” said Katie Abrams, an assistant professor at Colorado State University who researches consumer understanding of food labels. “And it’s going on in more places than just Colorado.”

GMO labeling will also be on the ballot in Oregon, and this year about 35 similar bills were introduced in 20 states.

If the measure passes in Colorado, by 2016 packaged or raw foods made with GMOs that are sold in retail outlets must be labeled with the phrase “produced with genetic engineering.” Exemptions include processed food intended for immediate human consumption, like at restaurants and delis.

Most processed food sold in America today, from beverages to baby food, include GMO ingredients such as corn syrup, corn oil, soy meal and sugar.

More than 90 percent of Americans believe the federal government should require GMO labels, according to an ABC News poll.

Supporters of the Colorado measure — including Natural Grocers and Eco-Justice Ministries — say mandatory labeling would create transparency for consumers, allowing them to choose what they want to serve at their family tables.

But opponents — including the Colorado Farm Bureau and the Rocky Mountain Agribusiness Association — say the measure would cost Colorado taxpayers millions of dollars, increase grocery costs for families, and create expensive new bureaucratic requirements that would hurt the state’s farmers.

As the vote nears, events that explore GMOs are popping up around the metro area, such as the Seeds of Doubt conference in Broomfield on Oct. 11, featuring researchers who’ve studied GMOs and their impact on health and environment.

GMO opponents believe that the process is harmful to health, pointing to studies that connect GMO with 65 health risks, from allergies to infertility. GMO supporters point to hundreds of peer-reviewed studies they say show the safety of genetically engineered foods. Both sides agree that no long-term human health studies have been conducted.

“It’s about education,” said Cheryl Gray, a registered dietitian who helped organize Seeds of Doubt. “We’re bringing in people involved in this world to tell their stories and bring their research forward. … Being consumers, we want to know, and we want transparency.”

Whole Foods, which supports the measure, will hold a tasting of non-GMO foods on Oct. 18 from noon to 3 p.m. at all of its Colorado stores.

And Monday at the sixth annual Chefs Collaborative Sustainable Food Summit in Boulder, there are two workshops on GMOs featuring such national experts as Gary Hirshberg, co-founder of Stonyfield Farm and chairman of Just Label It campaign.

“A lot of chefs are trying to practice a more natural and organic philosophy in cooking food,” said Michael Scott, lead chef instructor at the Auguste Escoffier School of Culinary Arts in Boulder. “If I have ingredients that I can’t find out are GMO produced or not, I can’t make a proper decision whether to use them or not.”

But many local farmers argue that the measure is unnecessary. They say there are already two food labels that identify foods without GMOs: the USDA Organic label and the Non-GMO Project verified seal.

“It would be a nightmare for me,” said Nathan Weathers.

At his family farm in Yuma County, they grow two kinds of corn — GMO corn and popcorn that has not been genetically modified.

They use the same combine to harvest both crops. Despite extensive cleaning of the equipment between those harvests, he says, if even a tiny bit of GMO corn ends up in a load of non-GMO corn, he won’t be able to sell it.

“There’s nothing that I could do with that load,” he said.

Paul Schlagel, a fourth-generation farmer in Longmont, says that genetically engineered seeds have allowed farmers to reduce their use of herbicides and increased their yield by 40 percent.

“After processing, sugar from genetically engineered sugar beets is molecularly the same as organic sugar, and our sugar in Colorado would be stigmatized by the label,” he said.

But the Rocky Mountain Farmers Union, a progressive organization dedicated to family farmers and ranchers, supports the measure.

“We’re not arguing about the science. We just think people have the right to know and make informed decisions on their own,” said Bill Midcap, director of external affairs.

“My problem is, how are they going to implement this on a state-by-state basis? How will Coca-Cola or Kellogg’s label their products specific to the market in Colorado?”

Supporters hope, and opponents fear, that labeling will lead to an economic boycott of GMO food products.

But experts aren’t so sure.

“Most research on consumer buying shows that people act on taste, price, convenience and other factors,” said Abrams of CSU. “They usually do what’s best for the wallet.”

Whole Foods isn’t waiting to find out. Last year, the company made the decision to label all food products if they contain GMOs, a massive project that should be complete by 2018. But small businesses like Denver Urban Homesteading say the costs created by mandatory labeling would put small markets out of business.

As the debate plays out in Colorado, Bradford Heap has already forged ahead, converting his two restaurants — Salt in Boulder and Colterra in Niwot — into GMO-free eateries.

It took six months to source all the products, from meat down to vinegar, making sure it wasn’t produced with corn.

Costs for some ingredients increased. Eggs went up by 33 percent, from $3 to $4 a dozen. But revenue has also increased this year: 25 percent at Salt and 15 percent at Colterra.

“It was born out of my frustration about my government’s inability to label anything or do anything significant around GMOs,” he said. “I decided to be the change I want to see.”

Colleen O’Connor: 303-954-1083, coconnor@denverpost.com or twitter.com/coconnordp

What is a GMO?

Genetically modified foods are derived from organisms whose DNA has been modified in a way that does not occur naturally, according to the World Health Organization. Most genetically modified crops have been developed to resist plant diseases or better tolerate herbicides. The most important GMO crops are corn, soy, cotton and canola. According to the FDA, most processed foods include some of these ingredients, like cornstarch in soups and sauces and corn syrup as a general purpose sweetener. Sugar is also included, because the sugar Americans consume either comes from cane or genetically engineered sugar beets.

On the ballot

Voters will be asked to vote on whether food that has been genetically modified or treated with genetically modified material should be labeled “Produced with Genetic Engineering” starting July 1, 2016. Foods that would be exempt include food from animals that are not genetically modified but have been fed or injected with genetically modified food or drugs; certain food not packaged for retail sale and intended for immediate human consumption; alcoholic beverages; and medically prescribed foods.