Q: Do carcinogens form with nuts if they are roasted at above 250 degrees? If so, should we stop eating nuts roasted at such temperatures?
A: This concern centers on acrylamide, a compound formed when certain plant foods are cooked at temperatures above 250 degrees, especially by frying, baking, broiling or roasting for long cooking times. Cooking causes a chemical reaction between sugars in the food and an amino acid called asparagine, which in turn forms acrylamide. Among the foods most noted for producing acrylamide are potatoes, leading to concerns about French fries and potato chips.
“Acrylamide is thought to possibly be a carcinogen in humans,” explains Joel B. Mason, MD, Tufts professor of medicine and nutrition. In 2011, the National Toxicology Program classified acrylamide as “reasonably anticipated to be a human carcinogen” because of studies in lab animals. But the American Cancer Society says, “Based on the studies done so far, it is not yet clear if acrylamide affects cancer risk in people.”
Acrylamide can indeed form when nuts are roasted, although the amount varies not only by degree of roasting but also by the type of nut. One 2005 study, for example, found higher levels in dark roasted almonds from the US, but significantly less in European-grown almonds and almost none in hazelnuts; the difference was linked to the amount of available asparagine in the nuts.
Testing by the US Food and Drug Administration has found wide variations in acrylamide content not only by food type but by brand. Levels in cashews and peanuts were very low or undetectable. Acrylamide amounts in almonds were higher but generally lower than in potato chips (which are typically consumed in greater quantity). Given the other health benefits of nuts, worries about acrylamide shouldn’t keep you from eating them as a substitute for less-healthy snacks.