Carcinogens in the Diet

It’s official. The federal government now has added agents commonly found in overcooked meat to the list of potential cancer causers.

On Jan. 31, the National Toxicology Program (NTP), part of the National Institutes of Health, published its latest update of materials known to cause cancer in people and others that are “reasonably anticipated” to do so. Among the 246 agents on the lists are the heterocyclic amines that develop in meats when they’re cooked too long at high temperature.

These aren’t the first listed items to be encountered primarily in the food people eat. Consider acrylamide. In 1991, NTP originally listed this common industrial chemical that’s used in the making of products from paper to permanent press fabrics. Yet acrylamide only became famous 3 years ago, when food chemists found that it can also form during the high-temperature cooking of foods, especially potatoes (see Acrylamide—From Spuds to Gingerbread).

Then there are aflatoxins, near ubiquitous fungal poisons that naturally lace a range of foods in tiny traces—especially peanut butter. This known human carcinogen was among chemicals on NTP’s first national compilation of cancer-causing agents, in 1980.

Most of the NTP lists are made up of industrial pollutants that contaminate air, water, and soil. Still, the primary route into people for some of these chemicals is through food. Included in this category of pollutants are the 1981 list entrants and now-banned compounds dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin) and polychlorinated biphenyls (PCBs). The latter are oily, dioxinlike materials used as electrical insulators in commercial equipment. Both dioxins and PCBs tend to enter the food chain as airborne pollutants that are picked up by plants.

A few NTP-listed carcinogens were, ironically enough, initially marketed specifically for use in or as foods. Among these were safrole, a flavoring once used in root beer and other foods, listed in 1981; butylated hydroxyanisole, or BHA, a common food preservative, listed in 1991; and alcoholic beverages, listed in 2000.

New additions

Key dietary additions to NTP’s two lists this year are heterocyclic amines best known by their abbreviations: MeIQ (2-amino-3,4-dimethlimidazo[4,5-f]quinoline), MeIQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline), and PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine). These chemicals join IQ (2-amino-3-methylimidazo[4,5-f]quinoline) as chemicals reasonably anticipated to be human carcinogens because they reliably cause cancer in test animals.

The new report observes, “Studies have consistently shown that MeIQ, MeIQx, IQ, and PhIP cause mutations” in organisms from bacteria to rodents. Moreover, it adds, heterocyclic amines appear to be more potent than other suspected environmental carcinogens at inducing genetic aberrations.

Finally, the report notes that while inconclusive, published studies in people “provide some indication” of human risks from eating broiled or fried foods “that may contain IQ and/or other heterocyclic amines.” The National Cancer Institute conducted one of those suggestive studies. It compared the diets of 176 stomach cancer patients and another 503 cancerfree individuals. Overall, people who regularly ate their beef medium-well or well-done faced more than three times the stomach cancer risk of those who ate their meat rare or medium-rare, according to a 1997 report of the research.

What the new NTP report doesn’t point out is that heterocyclic amines, of which there are at least 17, form in meat that has been cooked too long at high heat. Studies have shown that slower cooking at lower temperatures can prevent heterocyclic amines from forming. Other ways to prevent the chemicals’ formation include adding a little starch to meats (see How Carbs Can Make Burgers Safer), marinating them before cooking (see Well-Done Research), or precooking meat in a microwave oven for a few minutes prior to grilling (SN: 4/23/94, p. 264).

Deletions

The new NTP report contains an appendix of once-listed chemicals that are no longer deemed major cancer threats. Saccharin is a prime example.

This, the first no-calorie sugar substitute, celebrated its 125th anniversary last year. In 1981, NTP listed saccharin as a likely human carcinogen, noting that in male rats, saccharin proved a potent trigger of urinary cancers. However, that finding might be irrelevant to human risk, according to the new report.

The effects seen in male rats didn’t emerge in females or in mice of either gender. A review of the rat data eventually led scientists to suspect that the mechanism by which saccharin caused bladder cancer may be specific to the male rat. So, in 2000, NTP delisted saccharin.

As the new NTP report explains: “Although it is impossible to absolutely conclude that it poses no threat to human health . . . saccharin is not reasonably anticipated to be a human carcinogen under conditions of general usage as an artificial sweetener.”

How sweet.