Candy lines every inch of the mercado de dulces in Mexico City’s historic center. Tantalizing strawberry-flavored chocolates and Tajín-covered mango gummies pack the narrow aisles of the meandering marketplace. But many of the colorful packages are somewhat dampened by black stop signs printed on their fronts. Alongside dreamy descriptions of creamy and chocolatey confections, the stop signs warn “Excess calories” or “Excess sugars”. For some customers, the warnings are enough for them to pause and reconsider their purchases.

Latin America is leading the world in a movement to print nutritional warning labels on the fronts of food packages. Currently, the labels warn when a food product exceeds a consumer’s daily recommended value of any “nutrient of concern” – namely, sugar, salt or saturated fat (some countries have added trans fats, artificial sweeteners and caffeine). But research led by scientists across the continent is increasingly pointing towards another factor consumers may want to consider: how processed a food is.

Ultra-processed foods make up an increasingly large share of the average Latin American consumer’s diet. These industrially formulated products, which are often high in fats, starches, sugars and additives (like flavorings, colorings and preservatives), were first named and studied by Brazilian researchers in the early 2000s. Today, many Latin Americans get 20% to 30% of their daily calories from ultra-processed products (in the United States, the average is even higher – upwards of 60%). As the continent leads global research into the health impacts of ultra-processed foods, countries there are also taking steps to ensure labels end up on all ultra-processed products, warning consumers of these harms.

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In the early 2010s, researchers at the Pan American Health Organization, a regional office of the World Health Organization, began discussing the possibility of using front-of-package labels to combat rising rates of non-communicable diseases in the region.

“The initial proposals for front-of-pack labeling emerged because the information for consumers based on the nutrition facts table” was “completely insufficient for consumers to have a quick and easy understanding”, said Fabio Da Silva Gomes, the regional adviser on nutrition and physical activity for the Americas at the PAHO.

In 2010, Mexico became the first country in the region to move the “daily guidance amounts” label to the fronts of packages. (Today, some companies in the US voluntarily print daily guidance amounts on the fronts of packages in an industry-led program called Facts Up Front.) Then, in 2014, Ecuador introduced a “traffic light” label, which ascribed certain colors (red, yellow and green) to the levels of different nutrients in packaged foods.

But the landscape really changed when Chile implemented an entirely new label in 2016. Under former president Michelle Bachelet, who trained as a pediatrician, Chile implemented a sugary-drinks tax modification in 2014 and began studying front-of-package label designs.

In 2016, it implemented a black, stop-sign-shaped label after conducting research that found that the traffic-light label in use in Ecuador and much of Europe was too colorful (when associated with food, colors actually elicit cravings). Unfortunately, it was also confusing. Consumers didn’t know which was better: foods with yellow ratings for both sugar and sodium, or one red for saturated fat and one green for sugar. Additionally, the country banned the sale and promotion of products with warning labels in schools, restricted marketing of those products to children, and eventually fully banned companies from marketing foods with warning labels.

A 2021 study found that Chilean families purchased 27% less sugar and 37% less salt from foods labeled with “high in” warnings in December 2017, after the implementation of the label, than they would have if the labeling and advertising law had not been implemented.

The law also incentivized food companies to reformulate their products to include less salt and sugar so they wouldn’t be required to print a label.

From Chile, octagonal “warning labels” spread rapidly across Latin America.

Today, Peru, Uruguay, Mexico, Argentina and Colombia all mandate warning labels (with Venezuela expected to join them this December). Some countries have amended the warning label pioneered by Chile to capture more foods – like artificial sweeteners and caffeine – and others have introduced taxes to more strongly dissuade citizens from purchasing certain products.

But not all countries have followed the scientific consensus. When Brazil implemented its label in 2022, it introduced a design that was copied in Canada and may be replicated in the US. Instead of the black stop sign, Brazil printed a black-and-white magnifying glass next to a disclosure if the food was high in sugar, salt or saturated fat.

“We actually don’t recognize the Brazilian system as a warning system,” said Gomes. “It’s very small, and this is critical because we know from tobacco warnings that there’s a dose response between the size of the warning and the response of the consumer,” meaning consumers are less likely to purchase tobacco products the larger the warning label on them is.

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Latin America has, in some ways, had an easier time implementing front-of-package labels than the US because most countries’ constitutions there guarantee a right to health that supersedes commercial free speech. “There’s much less of an emphasis on protecting corporate free speech in particular, and there’s a strong emphasis on protecting children,” said Lindsey Smith Taillie, a professor of nutrition at the University of North Carolina at Chapel Hill’s Gillings School of Global Public Health. But corporations and trade groups have still fought back against labeling initiatives.

While lobbying legislators in countries considering labels, the international food industry has also threatened to take many governments to the World Trade Organization for allegedly violating free-trade agreements that prevent “unnecessary obstacles to international trade”. Gomes says that labels do not “restrict” the sale of ultra-processed foods, but rather add a “requirement” in order to market them.

The food industry has also funded research that emphasizes the importance of exercise over diet. Industry documents show that Coca-Cola gave university researchers in the US and Colombia $199,500 to study the role of physical inactivity, instead of the availability of whole foods, on obesity.

“The industry is really good about shifting the blame,” said Eric Crosbie, a professor in the School of Public Health at the University of Nevada, Reno. “What they were trying to do was shift the blame on to individuals so that they’re not responsible for their products. It’s a classic move that tobacco, alcohol, they’ve all done.”

Even where labeling laws are in force, companies have found ways around them. For example, some print a “front” on both the front and back of a package (but only print labels on one side). Or they package foods in an extra-clear plastic wrapper so they can print now-banned cartoon characters (to market to children) on the food itself.

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Although the concept of ultra-processed foods emerged in Latin America, no country there has a label demarcating UPFs. However, experts say countries are taking steps to change that.

“I would imagine that [UPF labels] would start in Latin America because they’ve been such a leader in this space,” said Taillie. “Ultra-processed food is a part of dietary guidelines in many of the Latin American countries”, whereas in the US “we’re hearing the evidence, but we don’t have it in our guidelines”.

And current warning labels already cover the majority of UPFs on the market because so many contain high levels of sugar, sodium and saturated fats.

“The evidence suggests that right now in Argentina, in Mexico, in Colombia, with the warning labels that we have applied with nutrient profile models, we can with very good confidence state that these countries are regulating at least 97, 98%” of ultra-processed foods, said Gomes. He noted these countries are also working to “fill this 2% gap” by marking foods that contain colorings, flavorings, emulsifiers and thickeners that are used to “mimic real food”.

Although the science around the various components of ultra-processed foods is still emerging, Gomes says the components still warrant labels because their purpose is simply to make unhealthy foods more appealing. “Think of tobacco legislation,” he says, pointing to laws that ban flavored tobacco products. “We do not necessarily need evidence on the harms of cosmetic additives to regulate them” because they are used “only for the purpose of stimulating the consumption of products that are harmful”.

Read more from this series:

• Ultra-processed foods are ultra bad for you. Here’s what to know

• The US food industry has long buried the truth about their products. Is that coming to an end?

• What are those weird ingredients in our favorite packaged foods?