Acrylamide: The Issue That Refuses to Die
By An interview with Carl Winter, Ph.D.
The acrylamide issue regarding food safety refuses to die no matter how many times food scientists shoot it down. Early studies of the chemical were aimed at workplace issues; construction workers in enclosed spaces such as tunnels were exposed to high concentrations of acrylamide, which is used as an adhesive. In some cases, such exposure led to cancer. The presence of far, far smaller amounts of acrylamide in certain foods, particularly fried foods with high carbohydrate content, quickly led to an ongoing food scare, one that has not subsided despite studies that show little or no correlation between acrylamide in food and common cancers.
Nevertheless, California, under its Proposition 65, requires warning labels in cases where toxic substances may be present in the environment, in workplaces, in water and in food products. Others require fast-food chains that serve french fries, the most common source of acrylamide, and some makers of potato chips to post warning signs and attach warning labels to their products. The food industry, worried that these measures would spread nationwide and affect sales of hundreds of different foods that range from bread to fries to coffee, strongly opposes such labeling and contends that the science underlying the issue is seriously flawed. It points to several studies that found no correlation between acrylamide intake and cancer, compared with a small study of humans and studies conducted with rats that did find a correlation. There are at present several lawsuits against California's EPA winding their way through the courts.
Food Safety Magazine spoke with Dr. Carl Winter, Ph.D., a toxicologist and head of the FoodSafe program at the University of California-Davis, to sort out the science behind the acrylamide issue.
Winter: As a food issue, this arose six years ago in a Swedish study aimed at assessing occupational exposure to acrylamide. As a control study, the scientists looked at people who had no occupational exposure and those control subjects showed the presence of acrylamide. The authors immediately contacted the World Health Organization with their data and the European Union and the Food and Drug Administration frantically began additional data collection. Risk assessments have now been conducted from both acrylamide levels estimated in foods and from epidemiological studies; conclusions from the risk assessments have varied dramatically. Still, it’s hard to prove a negative, and the very different methodologies of the various studies may mean we’re comparing apples and oranges.
FSM: How is acrylamide formed?
Winter: Formation requires a sugar and an amino acid, specifically asparagine, and heat. Asparagine is found in large concentrations in potatoes, which is why potato products have been singled out, but it is found in literally hundreds of foods. When heated in the presence of sugar, particularly through baking or frying, the amino acid and sugar react to form acrylamide.
FSM: Studies on rats have introduced levels of acrylamide up to 100,000 times the levels humans are exposed to. Is it fair to compare this extreme load to what humans would reasonably be exposed to?
Winter: It's a common risk assessment approach. In such studies, it's common to load animals up with as much of a substance as they can tolerate. You're stacking the deck to give you the best chance of catching a carcinogenic relationship.
By maximum tolerated dose, we mean something that doesn't significantly change the lifespan of the subjects. However, it places great stress on the organs of the test animals, and it has been argued that the response of the animals to this stress may lead to cancer. At much lower levels of exposure, organ stress may be much lower or nonexistent, thus preventing development of cancer in the animals.
A ratio of 100,000 to 1 may sound distorted, but it’s pretty typical. Again, the rationale for using such high doses is to maximize the potential to identify if the chemical causes cancer. What is much more difficult to assess is the probability, if any, of humans developing cancer and levels of exposure much lower than those studied in the animals. Keep in mind that the sensitivities of humans and the sensitivities of animals may be very different and that risk assessors often use very prudent riskenhancing methods to assess human risks by assuming humans may be much more sensitive than the animals under study.
FSM: What are the strengths and weaknesses of the various acrylamide studies?
Winter: One inherent weakness is extrapolating animal results to human beings. There are just so many variables, and focusing on the most sensitive animals may make the threat appear to be greater than it actually is. Also, people tend to misunderstand the results. Finding that there are three chances in a million of developing cancer is not the same as saying that three of a million people will develop cancer.
An alternative approach is to consider epidemiological cases; do people with higher exposure to acrylamide have higher risk of developing cancer? There are studies of people who kept track of their diet going back many years, and so far, no correlation has been found. This statistical approach is better, but it’s not perfect. If you find a 20 percent increase in cancer rates among those who consumed more acrylamide, you can be pretty certain it's not a random factor, but it may be due to a variable you didn't take into consideration.
On the other hand, finding no correlation is not evidence that no correlation exists. Your study just may not be sensitive enough. You can't ever prove no effect.
FSM: The food industry has pointed out that we have been cooking for millions of years and probably have a mechanism to detoxify acrylamides, while rats don't cook and may not have such a defense mechanism. Does that contention fly?
Winter: No. It’s hard to demonstrate either way. Our metabolisms are very different. But first of all, the evolution argument isn't all that convincing; as a species, we haven't cooked food all that long. I'm pretty skeptical of those claims. Rats may be just as able as humans to convert the substance metabolically. We have similar enzymes.
Rats may detoxify a chemical at one rate and humans may detoxify five times as much. Or not. We'd probably have to conduct feeding studies with rats, and compare the results to human blood or organs to determine the real detoxification rates.
FSM: Most of the studies so far seem to only examine specific cancers, mainly breast cancer in women and prostate cancer in men. Why were those singled out?
Winter: Simply because they're so common. If you were looking at a relationship with rarer cancers, you'd have a hard time finding enough cases to produce a viable study. There are plenty of breast and prostate cancer cases, and your chances of finding a correlation are far higher.
FSM: In your opinion, what is the actual risk from acrylamide in food products?
Winter: This may sound like a cliché, but nobody really knows. In reality, the risk is probably not zero but very close to zero. When compared with other risks that we might be exposed to, the risk probably isn't particularly high. Given the large number of people exposed to acrylamide in foods, though, it isn't surprising that regulatory agencies in the U.S. and throughout the world are taking this seriously.
Rather than consider the "actual" risk from acrylamide exposure, I think it's prudent to determine how our exposures to acrylamide in foods can be lowered either through food production and preparation practices that reduce acrylamide formation or through dietary changes that reduce the consumption of acrylamide-rich foods.
My research group is currently trying to model the recommendations of the Food Guide Pyramid and to develop an acrylamide exposure assessment that determine the differences in acrylamide exposure from those following the dietary guidelines recommended by the Food Guide Pyramid than from those with more typical food consumption patterns. Findings could demonstrate the impact of optimal food consumption patterns upon acrylamide exposure.
FSM: Acrylamide has been in the news, on and off, for several years. Why is this substance receiving so much attention?
Winter: It's not much different from many other substances that may be carcinogenic. It's the same general controversy, but this one involves food. And we all eat. Like many other controversies, there's a huge gray area, where solid science is replaced by assumptions and opinions. I'm hoping that our study, and studies by others, will quantify the argument better and shed light on some of these assumptions.
FSM: Do you see this controversy getting even more high-profile as other studies are performed?
Winter: It will continue; there's no immediate resolution in sight. But I'm not sure it will become a larger issue. The public is not all that concerned because they see acrylamide as a naturally occurring substance. It's not like an industrial pollutant, and evidence of harm to humans is pretty thin. But it will not go away in the foreseeable future.
Dr. Carl Winter is the Director of the FoodSafe Program and an Extension Food Toxicologist in the Department of Food Science and Technology at the University of California at Davis. His research and outreach work focus upon pesticide residues and naturally occurring toxins in foods.