Do you scrape the burnt bits off a piece of toast? Recent research suggests that might not be a bad idea…

You probably still have some of the eating and cooking habits that you picked up from adults when you were younger, perhaps without even realising it. Maybe you never lick your knife, or maybe you always throw salt over your shoulder to ward off evil spirits.

Many of these oddities are probably nothing more than superstition, but one in particular may have been unknowingly prescient a few decades ago, and was based on an undiscovered scientific discovery.

Scientists at the University of Stockholm discovered in 2002 that it may be beneficial to scrape the burnt bits off your toast. They discovered that when certain foods are heated above 120 degrees Celsius (248 degrees Fahrenheit), a substance known as acrylamide forms. Bread, biscuits, cereal, and coffee – and the amino acid asparagine reacts with the sugar content.

This is known as the Maillard reaction, and it is what causes food to brown and gives it its distinct flavour. However, scientists have discovered that acrylamide is carcinogenic in animals, but only at much higher doses than those found in human food.

According to the European Food Safety Authority, acrylamide may also increase the risk of humans developing cancer, particularly in children. However, researchers studying the effects on humans have yet to reach a definitive conclusion.

“After nearly 30 years as a ‘probable human carcinogen,’ there is still inconclusive evidence of its definite carcinogenicity in humans. However, if we continue to conduct human studies, we may have enough data to change acrylamide’s classification to a human carcinogen “Fatima Saleh, an associate professor of medical laboratory sciences at Lebanon’s Beirut Arab University, agrees.

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However, scientists are certain that acrylamide is neurotoxic to humans, which means it can harm the nervous system. The exact cause is unknown, but theories include acrylamide attacking structural proteins within nerve cells or inhibiting anti-inflammatory systems that protect nerve cells from damage.

Acrylamide’s toxic effects have been shown to be cumulative, which means that consuming a small amount of it over a long period of time may increase the risk of it affecting organs in the long run.

Animal studies suggest that long-term exposure to dietary acrylamide may increase the risk of neurodegenerative disease, such as dementia, and may be linked to neurodevelopmental disorders in children. Federica Laguzzi, assistant professor of cardiovascular and nutritional epidemiology at Sweden’s Karolinska Institutet’s Institute of Environmental Medicine, agrees.

“Because it has a low molecular weight and is soluble in water, acrylamide passes through all tissue, including the placenta,” says Laguzzi, who discovered a link between higher acrylamide intake in pregnant women and lower birth weight, head circumference, and length of their newborn babies.

The mechanism by which acrylamide may increase the risk of cancer in humans is unknown. Leo Schouten, an associate professor of epidemiology at Maastricht University in the Netherlands, has an explanation.

Following the discovery of acrylamide in our food by Swedish researchers in 2002, the Dutch Food Authority contacted researchers from the Netherlands Cohort Study on Diet and Cancer, including Schouten, to determine whether dietary acrylamide posed a risk to humans. Based on a questionnaire, Schouten and colleagues attempted to estimate how much acrylamide people consumed.  

The mechanism behind acrylamide’s potential cancer-causing effect could be related to hormones

They discovered that the difference between people with low and high acrylamide exposure in an elderly Dutch population could be explained primarily by one popular Dutch product called ontbijtkoek, roughly translated as “breakfast cake,” which was extremely high in acrylamide due to the use of baking soda in the production.

They looked into the relationship between nonsmokers’ acrylamide intake (because smoking also contains the substance) and all cancers and discovered a higher risk of endometrial and ovarian cancer in women who were exposed to a lot of acrylamide. Further research has revealed a possible link between acrylamide consumption and kidney cancer.

However, no other researchers have yet to confirm these findings. A population study in the United States comes the closest. which published findings in 2012 indicating an increased risk of ovarian and endometrial cancer in nonsmoking postmenopausal women who consumed high levels of acrylamide. Of course, there could be other reasons for this; people who consume high levels of acrylamide may also engage in other risky behaviours.

Other studies either did not find an association or found weaker associations. However, it is unclear whether the association discovered by Schouten and his colleagues was incorrect, or if other studies were unable to accurately measure acrylamide intake.

According to Schouten, the mechanism underlying acrylamide’s potential cancer-causing effect could be related to hormones, because certain hormones have been linked to an increased risk of cancer, particularly female genital cancers such as endometrial and ovarian cancer.

“Acrylamide may affect oestrogen or progesterone, which would explain female cancers,” says Schouten.

Laboratory studies on rats have also discovered links between acrylamide consumption and cancer in the mammary glands, thyroid gland, testes, and uterus, implying a hormonal pathway, but this does not automatically imply a similar risk in humans.

More long-term studies on the link between acrylamide and cancer are needed, according to the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives in 2010. However, it did support efforts to reduce acrylamide levels in food.

One of the most difficult challenges, however, is accurately measuring how much acrylamide we consume.

“While it is well established that acrylamide is genotoxic and can cause cancer in animals, the link between acrylamide and cancer in humans remains unknown,” Laguzzi says. “Most epidemiological studies use dietary questionnaires to measure acrylamide intake, which relies on people’s reporting, which can bias the results.”

While Schouten believes he was able to accurately measure acrylamide in people’s diets, many toxicologists disagreed. Another method for measuring acrylamide intake is to measure biomarkers in urine and blood, but this hasn’t yielded any concrete results, according to Schouten.

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