Can burnt toast cause cancer? A doctor explains the tricky science

It’s the crispy, forbidden crunch of an overtoasted marshmallow or the acrid mouthfeel of blackened toast smothered in jam.

Whether a culinary accident or an exercise in digestive boundary-pushing, it’s no surprise that we’ve all eaten our fair share of burnt foods. But is this relaxed approach to food safety really as harmless as you think?

Maybe you’ve heard eating burnt food can make you sick. Or maybe, after a quick Google, you’ve read blogs that claim that eating burnt food — from slightly blackened barbeque to scorched toast — will fill your body with cancer-causing carcinogens.

In 2017, the U.K.’s Food Standard Agency even launched a campaign against the consumption of darkened food, telling diners to “Go for Gold” with their food’s color instead.

Rashmi Sinha is a senior investigator at the National Cancer Institute whose research focuses on the dietary exposures and biological mechanisms of cancer risk. She tells Inverse that determining whether or not burnt food really poses a cancer risk is more complicated than it seems.

While the chemical reactions associated with burnt food have been found to contribute to the development of cancer in animals “in humans, it’s not clear,” Sinha says. Ultimately, most nutritional advice boils down to: eating a little bit of burnt food doesn’t mean you’ll be harmed, but you should avoid eating it whenever possible.

What happens when you burn your toast?

When we apply heat to food — especially when we sear or grill it — there’s a delicious chemical reaction that takes place called between chains of proteins and simple sugars in our food that causes caramelization and shades of brown and black. Known as the Maillard reaction, this transformation is coveted for its ability to concentrate flavor in food.

However, more than flavor can emerge.

Sinha says researchers have also identified several other chemical reactions sparked by the Maillard reaction that may be harmful to human health. These include:

• Acrylamide
• Heterocyclic amines (HCAs)
• Polycyclic aromatic hydrocarbons (PAHs)

HCAs and PAHs typically develop during the cooking of meat and are respectively created either through the binding of proteins, sugars, and fats or through the creation of smoke via dripping juice. Acrylamide, on the other hand, is a little more multi-purpose and can be found in everything from burnt coffee to french fries and even cigarette smoke.

In the body, these three compounds can corrupt pieces of your DNA and create potentially dangerous mutations. However, despite this evidence, national health institutes are cautious to declare these compounds as definite carcinogens, i.e. cancer-causing.

Can burnt food give you cancer?

Here’s what we know for sure, Sinha says: HCAs and PAHs have been shown to contribute to cancer development in animal models (including monkeys) and acrylamide has been shown to contribute to cancer development in rodents models.

However, confirming these results in human models is a lot trickier — both logistically and ethically.

“The main studies have been association [or] prospective studies in which we ask questions about how [healthy participants] cook their foods and then we follow them up for ten, fifteen, twenty-years and compare people who had cancer with no cancer to see if there's anything associated with the way that they cook the foods,” Sinha explains.

But association studies are “observational in nature,” Sinha says. “To really be able to be to say that this causes cancer you need to do clinical trials. But you can’t do clinical trials with things that are possible carcinogens.”

In other words, while these trials can at best show a correlation between cooking methods and cancer, they can’t prove causation.

For acrylamide, in particular, human observational trials have thus far reported mixed results with some concluding the compound contributes little to no cancer risk and others finding that it does. Similarly, knowing at what concentration these compounds become dangerous is also challenging because it can vary widely across food types and preparations.

In the cases where acrylamide and HCAs/PAHs were found to contribute to cancer risk, the cancers they were linked to included:

• Ovarian cancer
• Endometrial cancer
• Colorectal cancer
• Pancreatic cancer

But ultimately, we just don’t know for sure whether or not these compounds are truly cancer-causing when consumed in food, Sinha says. This doesn’t mean that scientists aren’t working toward the answer.

Of particular interest for this kind of research is identifying biomarkers that can be identified in a person’s blood or urine, Sinha says. This would allow researchers to say for sure the level of acrylamide or HCA/PAH exposure.

How to safely eat burnt food

While the official designation of these compounds as carcinogens may still be out, there are still steps you can take today to lessen your potential risk from these foods, Sinha says.

Mainly, avoid cooking your meat, vegetables, or bread at excessively high heat whenever possible.

This doesn’t necessarily mean you can never barbeque again. Instead, try mixing in a few non-direct heating methods as well such as using sous vide to lock in flavor. If you are grilling or frying your food, look for it to turn golden instead of dark brown or black, and make sure you have proper ventilation.

As for that black toast you’re powering through: this is your sign to go grab another piece of bread and try again.

CHECK, PLEASE is an Inverse series that uses biology, chemistry, and physics to debunk the biggest food myths and assumptions.

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