Not too long ago I reviewed Michael Pollan’s book Cooked, and thought it an overall good read. Buried beneath the heaps of praise Pollan offers the habit of cooking, he acknowledges, almost in passing, the fact that cooking food can produce toxins. In a former life I earned a masters degree in environmental chemistry, toxicology and risk assessment, so anytime the word ‘toxin’ is mentioned my ears perk up, particularly when I hear it in the same sentence as the word ‘food’.
In fact, there are several types of toxins created by cooking, compounds that are the direct result of one chemical in food reacting with one or more other chemicals in the presence of heat to create another compound that exhibits toxic effects in people. Given the importance of cooking in today’s culture, and given that so few people seem to be aware of these toxins, I think it worthwhile to dedicate a series of posts to them. The first of the cooking-created toxins I’ll look at are hetercyclic amines, often abbreviated as HCAs.
Heterocyclic amines are a class of compounds formed when amino acids, sugars and either creatine or creatinine, compounds found in the muscle tissue of animals, react at high cooking temperatures . In particular, HCAs tend to form preferentially when meats are cooked at temperatures above 300 degrees Fahrenheit, as happens during grilling, broiling and frying. HCA formation is also enhanced when meats are cooked for extended periods of time, irregardless of temperature. HCA’s in their native state aren’t toxic, but become so once bioactivated within our bodies by one of our cytochrome P450 enzymes [2, 3].
Several HCAs are either documented or suspected carcinogens in humans, and can form adducts on DNA that can cause mutations or other genetic damage [1-3]. Evidence linking HCA consumption to specific types of cancer is mixed, with some studies finding links while others fail to do so . This isn’t surprising, given how challenging it is to collect adequately detailed – and accurate – epidemiological data on a large enough sample of people to yield meaningful results. Nonetheless, some of the more recent, and better designed, studies have convincingly linked HCA consumption with cancers of the colon, prostate, lung and breast, among others [5-9]. One study that failed to find a strong overall correlation between HCA consumption and cancer seemed to contradict itself by noting that, among its participants, those with the highest recorded levels of HCAs were individuals who suffered from cancers of the colon, bladder and kidneys .
This isn’t to say that HCA exposure is a sole or even dominant contributor to these or other cancers. In fact, attempts to estimate the risk of developing cancer as a function of HCA exposure range widely, from 1 in 10,000 exposed individuals to as high as 1 in 50 . Dose obviously matters, as does exposure frequency. Metabolic variation plays a role too, as the enzymes that activate HCAs and thereby contribute to their carcinogenicity are more active in some people than in others . And, of course, other dietary and lifestyle factors besides exposure to HCAs also play substantive roles in the etiology and progression of all types of cancer.
Heterocyclic amine ingestion due to the consumption of foods – particularly meats – cooked at high temperatures and for extended periods of time are linked to cancer in human beings consistently enough that I feel the relationship between consumption of these compounds warrants more attention among health practitioners, nutritionists and consumers more broadly. Most of the studies completed to date focus primarily on the potential of HCAs to contribute to cancer, but given their documented mutagenic activity they may well contribute to the emergence of other diseases as well. Hopefully readers will be inspired to better inform themselves about this and other heat-created toxins formed by cooking.
- Hetercyclic Amines, in the Report on Carcinogens, 12th Ed., National Toxicology Program, United States Department of Health and Human Services.
- Comments on the history and importance of aromatic and heterocyclic amines in public health. J. Weisburger, Mutation Research, 2002, Vol. 506-507, Pgs. 9-20.
- Heterocyclic amines: mutagens/carcinogens produced during cooking of meat and fish. T. Sugimura, et al, Cancer Science, 2004, Vol. 95, Pgs. 290-299.
- Problems associated with the determination of heterocyclic amines in cooked foods and human exposure. K. Skog, Food and Chemical Toxicology, 2002, Vol. 40, Pgs. 1197-1203.
- Analysis of total meat intake and exposure to individual heterocyclic amines in a case-control study of colorectal cancer: contribution of metabolic variation to risk. S. Nowell, et al, Mutation Research, 2002, Vol. 506-507, Pgs. 175-185.
- An epidemiologic approach to studying heterocyclic amines. R. Sinha, Mutation Research, 2002, Vol. 506-507, Pgs. 197-204.
- Heterocyclic amines, meat intake, and association with colon cancer in a population-based study. L. Butler, et al, American Journal of Epidemiology, 2003, Vol. 157, Pgs. 434-445.
- A large prospective study of meat consumption and colorectal cancer risk: an investigation of potential mechanisms underlying this association. A. Cross, et al, Cancer Research, 2010, Vol. 70, Pgs. 2406-2414.
- Meat consumption, cooking practices, meat mutagens, and risk of prostate cancer. E. John, et al, Nutrition and Cancer, 2011, Vol. 63, Pgs. 525-537.
- Dietary heterocyclic amines and cancer of the colon, rectum, bladder and kidney: a population-based study. K. Augustsson, et al, The Lancet, 1999, Vol. 353, Pgs. 703-707.
- Health risks of heterocyclic amines. J. Felton, et al, Mutation Research, 1997, Vol. 376, Pgs. 37-41.