What You Need to Know About Process Contaminants

Process contaminants are chemical compounds that form in some (typically starchy) foods, most commonly when they are heated to a high temperature—as when frying, baking, or canning. They can also form when some foods are dried or fermented. 

They are not new. In fact, because these chemicals are created whenever certain foods are cooked at high heat, humans have been consuming them for at least as long as we’ve been toasting bread, frying potatoes, and making corn chips. Unlike lead, PFAS, and other adulterants that enter the food chain from external sources such as contaminated soil, process contaminants form naturally as a result of chemical reactions in the food itself.

But food safety experts have only discovered over the past two decades just how widespread process contaminants are in the foods we commonly eat. Not all of them are harmful, but in animal studies, high doses of some have been shown to cause cancer, genetic mutations, and neurological issues. 

CR recently tested several popular foods for three of the most common process contaminants—acrylamide, furan (and four of its metabolites), and 4-methylimidazole, which is also known as 4-MEI. The levels of furan (and its metabolites) and of 4-MEI that CR found in nearly all of the foods tested are considered within an acceptable margin of safety by CR food experts and leading global health authorities. But our food experts were concerned with the amount of acrylamide found in a variety of popular foods that many people consume frequently, including french fries and potato chips, chicken nuggets, coffee, and breakfast cereals.

Acrylamide is a chemical that has been used for industrial purposes, including wastewater treatment and paper manufacturing, since the 1950s. It is also present in cigarette smoke (smokers have among the highest levels of acrylamide in their bloodstream). But it was not discovered in food until 2002, when Swedish scientists studying workplace exposure to the chemical unexpectedly found high levels in the general population and were able to link it to certain foods. 

It forms naturally in plant-based foods, including potatoes, plantains, and grains, when an amino acid called asparagine interacts with sugars under high heat and produces a golden-to-brown coloring on the surface of the food in what is known as the Maillard reaction.

Because it is a byproduct of frying, toasting, and baking, it is extremely common and found in an array of foods served at home, in restaurants and fast-food chains, and sold on supermarket shelves. One 2008 study estimated that at least 30 percent of the calories in a typical diet contain acrylamide, and CDC monitoring has shown that nearly the entire U.S. population, including children, has some level of acrylamide in their bloodstream. 

In animal studies, acrylamide has been shown to be a neurotoxin that can also cause cancer and have adverse effects on male reproduction. But any evidence of a link between dietary acrylamide and cancer or other health effects in humans remains limited and inconsistent. 

The Environmental Protection Agency and the International Agency for Research on Cancer have classified acrylamide as a probable human carcinogen (red meat carries the same classification). The American Cancer Society’s website says that reviews of epidemiological studies “suggest that dietary acrylamide isn’t likely to be related to risk for most common types of cancer.” But it also notes that ongoing studies will continue to yield new information. In 2015, the European Food Safety Authority (EFSA) conducted a risk assessment and concluded that acrylamide in food potentially increases the risk of cancer.

After testing thousands of food samples for acrylamide between 2002 and 2015, the FDA concluded that "the continued presence of acrylamide in food suggests efforts to reduce acrylamide should continue." In 2016, the agency issued guidance to the food industry on ways to reduce acrylamide levels (by, for instance, frying potatoes at lower temperatures and for shorter times), noting that doing so “may mitigate potential human health risks from exposure to acrylamide.” These mitigation measures are entirely voluntary.

The FDA has not identified any benchmarks or maximum allowable levels of acrylamide in foods and does not require any labeling to identify the presence of acrylamide. Its website says that the agency is currently conducting research to determine if the levels of acrylamide found in food pose a health risk to people, but it also says the last time it posted any testing data was in 2019 (the most recent testing data posted is from 2015). 

“It’s not clear whether or not the FDA is still monitoring food for acrylamide,” CR’s Akinleye says. (The FDA did not respond to CR’s requests for comment.) “We believe this lack of action suggests that the FDA does not see acrylamide as a concern, but we think that it could be a concern, especially for people who frequently consume foods that contain high levels of it.”

Selina Wang, PhD, a chemist at the University of California, Davis, who runs a lab that researches food quality and purity, says that more needs to be done. “The U.S. has made some progress, but not enough to match the risk or protect vulnerable populations,” she says, explaining that the low body weight of infants, toddlers, and young children relative to adults results in higher acrylamide exposure.

The European Union has taken a more active approach to monitoring and lowering acrylamide levels in certain foods. Since 2018, most businesses that make or serve food have been required to monitor and reduce acrylamide to levels that are “as low as reasonably achievable.” While it has not set limits on the amount of acrylamide permitted in food, the EU has set benchmark levels for food producers to gauge the effectiveness of mitigation measures. The EU does not require any labeling regarding acrylamide in packaged food products. “It’s reasonable to assume that EU consumers are exposed to lower acrylamide levels than Americans, due to the EU’s mandatory mitigation measures, benchmark levels, and monitoring,” Wang says.

California has perhaps the most stringent regulations on the books. The state established a “no significant risk level” (NSRL) threshold based on cancer risk from acrylamide and also set several concentration levels specific to particular foods. In general, if a product exposes someone to a carcinogen listed under California’s Proposition 65 law, a warning is required unless the exposure is below the NSRL (coffee is exempt from the requirement). 

To meet their Proposition 65 obligations, California businesses that provide foods that expose consumers to acrylamide could warn them by using product labels or signage at restaurants. However, in 2021, a district court temporarily stopped the enforcement of the warning requirement for acrylamide in food based in part on the lack of scientific consensus on the carcinogenicity of acrylamide at the levels found in food. This year, a new court order made the injunction against enforcement permanent. The state’s attorney general has appealed the order.

CR tested 55 popular supermarket food products and 11 fast food items, some of which were among those previously tested for process contaminants by the FDA. In 73 percent of the products tested (48 of 66), the estimated intake of acrylamide in one serving exceeded the benchmark set by European food regulators to protect against cancer risk, while 77 percent (51 of 66) of the foods tested exceeded California’s more stringent limit.

Acrylamide levels varied widely, even among similar foods, but hash browns, chips, graham crackers, popcorn, and french fries had the highest acrylamide levels, on average.

“Based on our findings, we believe that the FDA needs to resume testing for acrylamide and other process contaminants in food, reopen their risk assessment of acrylamide, and set exposure limits that are adequately protective of health,” CR’s Akinleye says.

Wang agrees the FDA should continue monitoring acrylamide levels and promoting ways to keep them as low as possible, but cautions that it could be difficult to set strict limits without discouraging people from eating otherwise healthy foods like whole-grain bread or roasted nuts. “Rather than imposing hard limits, FDA could set health-based reference points for safe exposure levels and use those as guidance values, as European food safety authorities have done,” she says. 

Owen McDougal, PhD, a chemist and professor at Boise State University who has studied ways to lower acrylamide levels in foods, says that continued government testing and studies are needed to help determine what risk acrylamide in food actually poses. “While no link to adverse human health effects due to acrylamide has been definitively made, continued studies are required to confirm or dispute appropriate levels for consumption.” 

He adds that, although there are many ways to reduce acrylamide levels in commercially prepared foods, they would likely increase the cost. “The food industry has the tools to make products with less acrylamide, but at present not much is being done because the consumer would likely have to pay more for them. The focus is on economics more than it is on health and well-being.” 

Because the dietary risks to humans posed by acrylamide in food are still being studied, CR and other food safety experts stress that acrylamide in the diet is currently an issue that requires prompt government action and increased public awareness rather than alarm. 

“We’re not saying that people should stop eating these foods,“ CR’s Akinleye says. “Any harmful effects from acrylamide would result from daily exposure over time, so there’s no cause for panic. But if you consume these foods regularly, you could be exposing yourself to levels of acrylamide that can cause harm.” He says that reducing how much of these foods people eat and how often they eat them, as well as being mindful about how the foods are prepared, can reduce levels of exposure. 

McDougal says that trying to eliminate acrylamide from your diet is not a realistic or desirable approach. “Acrylamide is a part of the human diet. We won’t be rid of it, but we can implement processing technology and conditions that minimize exposure, and posting the acrylamide level on product labels would allow consumers to make informed decisions.” 

Until that happens, taking the following steps can help reduce the amount of acrylamide in your diet.

Reduce how much of these foods you eat, and how often. “We recommend that people reduce their consumption of these foods by eating smaller portions and reserving them for an occasional treat,” Akinleye says. Wang notes that there are other good reasons to reduce consumption of many foods that contain acrylamide: “I would advise reducing frequent consumption of fried and baked snack foods not only because of acrylamide, but also because they tend to be calorie-dense and nutrient-poor. The best approach is to maintain a balanced diet with limited processed or fried foods.”

Vary cooking methods. Frying produces the highest acrylamide levels in potatoes and other starchy vegetables such as plantains, followed by roasting and baking. Boiled or microwaved potatoes contain virtually none.

Aim for golden, not brown. When frying or roasting potatoes, plantains, or similar vegetables, cook them to a light or golden yellow color. The darker the browning, the more acrylamide forms. The same rule applies to toast—lighter is better.

Soak potatoes before cooking. Soak raw potato slices in water for 15 to 30 minutes, then pat them dry before frying or roasting. (Soaking may slightly change the texture or mouthfeel of the cooked potato.)

Don’t refrigerate potatoes. Cold storage increases their sugar content, which can lead to higher acrylamide levels when cooked. Instead, keep potatoes in a dark, cool, well-ventilated place.

Make or buy thicker fries. Acrylamide forms near the surface of food, so thicker fries—with their lower surface-area-to-volume ratio—tend to contain less per gram.

Make or buy thinner potato chips. Thin chips cook faster and require less heat, which helps limit acrylamide formation.

Eat sweet potato fries and chips in moderation. They typically contain more acrylamide than regular versions.

Pick dark-roast coffee. Light-roast coffee beans retain higher levels of acrylamide.

Keep frying temperatures moderate. The higher the frying temperature, the more acrylamide is formed. Fry foods at 338° F (170° C) or lower. (If large bubbles form quickly when you dip a wooden spoon handle or chopstick into the oil, it’s too hot.)