Hold the fries.
A Poster adorning the walls of Kentucky Fried Chicken restaurants in California may just take your appetite away. Or at least make you consider giving up the fries. It says "Cooked potatoes that have been browned, such as french fries, baked potatoes and potato chips, contain acrylamide, a chemical known to the state of California to cause cancer." Is California really privy to some information that has eluded the rest of the world? No. But the state does have a unique law, Proposition 65, which states that "no person in the course of doing business shall knowingly and intentionally expose any individual to a chemical known to the state to cause cancer or reproductive toxicity without first giving clear and reasonable warning to such individual." So, is the warning about acrylamide reasonable?
Concern over this chemical first appeared in 2002 when Swedish researchers detected it in a variety of foods ranging from french fries and bread to cereals and coffee. Alarm spread quickly because acrylamide, a known carcinogen, was now turning up in food. The chemical's toxicity had been extensively studied because of its long history as a precursor to polyacrylamide, a chemical widely used in water treatment and cement manufacture. Since it had been found to cause cancer in animals, as well as neurological problems in people, strict guidelines for occupational exposure had been formulated. Nobody had expected acrylamide to appear in food. Yet there it was. How did this industrial chemical contaminate such a wide range of foods?
It didn't take long for chemists to solve that problem. Acrylamide wasn't an outside contaminant, it was actually being formed in the food! It had always been there, it just hadn't been detected before. That's somewhat surprising because the reaction responsible for the formation of acrylamide, the Maillard reaction, had been the subject of numerous investigations since it was first described in 1912 by the French chemist Louis Camille Maillard. When sugars are heated with amino acids, Maillard discovered, they form a wide range of compounds that are responsible for the flavour and colour of many common foods. Bread crust, pretzels, roasted coffee, popcorn, grilled onions and fried potatoes all owed their flavour and colour to a host of reactions between various sugars and amino acids. The product of asparagine--an amino acid and a common constituent of proteins--reacting with glucose? Acrylamide!
Any ingested acrylamide is considered by the body to be an undesirable foreign intruder. Our detoxicating systems go to work and gear up to get rid of the chemical either by excreting it directly through the kidneys, ferrying it out of the body by linking it to glutathione, or enzymatically converting it to urine-soluble glycidamide. But the problem is that both acrylamide and glycidamide are very reactive molecules and can damage important biomolecules such as proteins and nucleic acids before they are eliminated. Glycidamide in particular is a known carcinogen and a possible reproductive toxin.
There is no doubt that acrylamide can cause cancer in animals, but can it do so in humans? That's a tough question to answer. The doses that cause cancer in animals are at least a thousand times greater than the amounts of acrylamide to which we are exposed through common dietary sources. But the possibility that exposure of humans to small doses over a long period of time may have an effect similar to large doses in animals over a short period cannot be ruled out. That is why, since the original detection of acrylamide in the diet back in 2002, a large number of case-control and cohort epidemiological studies have explored this possibility.
In a case-control study, subjects with a particular disease are compared to a similar group of healthy people. All are questioned about their lifestyle and dietary habits in an attempt to find a possible connection to the disease. In a cohort study, a large number of healthy people are followed for years to see what disease patterns emerge. Again, attempts are made to find a link between lifestyle factors and disease.
Over two dozen such studies have investigated the possible connection between dietary acrylamide and various cancers. No association has been found with colorectal, bladder, breast, brain, prostate, thyroid, lung, gastric, esophageal or pancreatic cancers. The only cancers where the epidemiological studies are inconsistent are kidney, ovarian and endometrial cancers, with some researchers noting a possible association. Overall, the data do not support a link between dietary aerylamide and cancer. It is also noteworthy that coffee accounts for almost half of our dietary acrylamide intake and coffee consumption has not been linked with any sort of cancer.
Still, because acrylamide is an animal carcinogen, Health Canada has added it to its list of toxic substances and is urging the food industry to take steps to reduce our exposure to the chemical. Various methodologies have already been developed, including baking and frying at lower temperatures (below 120 degrees Celsius) and reducing the levels of sugar and asparagine in foods susceptible to acrylamide formation. A clever technique involves the addition of asparaginase, an enzyme isolated from a strain of the mould Aspergillus oryzae, which is commonly used to ferment soybeans for soy sauce. But some people are concerned about adding yet another chemical to our food supply, even though Health Canada has deemed it safe. Given the lack of evidence for dietary acrylamide causing cancer, maybe the question we should be asking isn't whether asparaginase is safe or not, but whether we are looking for a solution to a problem that doesn't exist.
Joe Schwarcz is the director of McGill University's Office for Science and Society.
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