Heterocyclic Amines (HCAs) and Polycyclic Aromatic Hydrocarbons (PAHs): The chemicals in grilled and cooked meats that increase the risk of individuals developing cancer.

In October of 2015 the International Agency for Research on Cancer (IARC) which is the cancer research division of the World Health Organization (WHO) issued a report on the link between processed meats and colorectal cancer labeling processed meat as a carcinogenic to humans. They also labeled red meat as probably carcinogenic to humans, showing “strong mechanistic evidence supporting a carcinogenic effect” (Terrassee and Gaudin, 2015). The IARC WHO report was able to provide strong links and evidence between the consumption of red and processed meats and colorectal, pancreatic, and possibly prostate cancer. There are also substances produced when cooking animal flesh that should be considered in the development and potential progression of cancer. The WHO (2015), recognizes that there are other potential carcinogenic qualities of red meat such as haem iron and N-nitroso compounds and polycyclic aromatic hydrocarbons which are also found in other foods and air pollution (para, 18).

Heterocyclic Amines (HACs) and Polycyclic Aromatic Hydrocarbons (PAHs) are mutagenic substances and carcinogenic compounds formed when cooking muscle meats (Cross and Sinha, 2004, p. 49).

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What are Heterocyclic Amines and Polycyclic Aromatic Hydrocarbons, where are they found, and how are they formed?

Heterocyclic Amines (HCAs) are not found naturally in animal products. These compounds are formed when muscle meats are cooked at high heat (National Cancer Institute [NCI], para. 1, 2015). Research conducted by NCI (2015) has concluded that “Amino acids (the building blocks of proteins), sugars, and creatine (a substance found in muscle) react at high temperatures” to form HCAs. Polycyclic Aromatic Hydrocarbons (PAHs) are formed differently than HCAs. According to the NCI (2015) “PAHs are formed when fat and juices from meat grilled directly over an open fire drip onto the fire, causing flames. These flames contain PAHs that then adhere to the surface of meat” (para. 2). According to NCI (2015) the charring of all foods increases the amount of PAHs as does the burning of gas and cigarettes (para. 3).

Dr. Neal Barnard on the Dangers of Grilled Meats

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How many different types of heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are formed in cooked meats?

According to Zaidi, Kumar, and Rawat, (2012) “more than 24 different types of food mutagens have been identified till date from cooked meat products” (p. 2897). According to Cross and Sinha, (2004) “more than 100 types of polycyclic aromatic hydrocarbons (PAHs) exist but extensive knowledge is only available for one of the carcinogenic PAHs, benzo(a)pyrene (BaP)” (p. 49).

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Do heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) increase our risk of developing cancer?

According to the National Cancer Institute ([NCI], 2015) “HCAs and PAHs have been found to be mutagenic-that is, they cause changes in DNA that may increase the risk of cancer” (para. 1). According to Layton, et al., (1995) research recognizes that consuming animal flesh, meat and fish, cooked under normal conditions contains PhIP, a “potent mutagen”, linked to an individual’s risk of developing cancer (p. 39). This research has also been followed up by other researchers who found that “MelQx and PhIP are two potent genotoxic chemicals which are formed” when meat is cooked and their research determined that “PhIP is a more potent mammalian cell mutagen” than MelQx (Gooderman et al., 1997, p. 53).  According to Sinha (2002), high temperature cooking of animal flesh has been linked to an increase in mutagenic and carcinogenic compound Heterocyclic Amines (HCAs). The temperature in which meat is cooked plays a significant role in the formation of HCAs. Cooking meat at higher temperatures increases the levels of HCAs within the meat while cooking at low temperatures decreased levels of HCAs contained within the meat (p. 8034).

However, HCAs are not the only mutagenic and carcinogenic compound found in the cooking of animal flesh such as beef, pork, fish or chicken, but polycyclic aromatic hydrocarbons PAH are also chemicals formed when these muscle meats are cooked at high temperatures by means of pan frying, open flame grilling, or smoking (Cross and Sinha, 2004, p. 49).

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Can scientist and researchers measure heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) within the body?

Yes, according to Holland, et al., (2005) the presence of “8-MeIQx and PhIP were identified in the urine of meat eaters but not in the urine of subjects who refrained from meat consumption for >24 h or in urine of vegetarians” (p. 586). Levels of HCAs and PAHs drop to non-detectable levels after 24 hours after not consuming meat thus decreasing the risk of having these HCAs and PAHs circulating through the blood stream (Holland, et al., p. 583). However, if individuals consume grilled meat 2 or 3 times a day these levels can stay elevated. Those who do not consume meat products, vegetarians and vegans, have a greatly diminished risk of consuming HCAs and PAHs.

Other researchers have examined breast tissue from women undergoing reduction mammoplasty, or breast reduction surgery. What these researchers found was that the consumption of HCAs and possibly PAHs which are found in processed, fried, and stir-fried meat were directly correlated to the amount of DNA mutation, or carcinogenic metabolites, found in human breast tissue (Rohrmann, Jung, Linseisen, and Pfual, 2009, p. 127).  While further research to detect HCAs and PAHs within the body were carried out by DeBruin, Martos, and Josephy (2001) who found PhIP in human breast milk of lactating mothers “detection of PhIP in milk indicates that ductal mammary epithelial cells are directly exposed to this carcinogen, suggesting that heterocyclic amines are possible human mammary carcinogens” (p. 1526-1527).

Even hair can provide a relevant marker of Heterocyclic aromatic amine exposure. According to Bessette et al. (2009) researchers have observed increased concentration of PhIP in human hair of those individuals who eat vegetarian and smoke leading them to state that “hair appears to be a promising long-lived biomarker with by which we can access the exposure to PhIP, a potential human carcinogen”(p. 1454). According to other researchers “Heterocyclic aromatic amines (HAAs) are one class of ubiquitous mutagens found in cooked meats, poultry, fish, and tobacco smoke condensate” (Holland et al., 2005). Therefore, even if individuals who do not consume meat they can still be exposed to these chemical mutagens if they smoke cigarettes.

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How can I decrease my consumption of heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) and lower my risk of developing cancer?

Varying cooking methods and duration of cooking times were noted as possible ways to decrease the exposure to these harmful HCAs and PAHs. “Meat cooked until well/very well done and/or by higher-temperature cooking techniques such as grilling” increase HCA and PAH levels in meat according to (Sinha, 2002, p. 197). As explained above the presence of these substance may be explained in part due to the cooking method one follows in preparing meat. This may also explain why some studies find that meat cooked at high temperatures over open flames such as grilling and/or barbequing may increase the risk of HCAs and PAHs while other low temperature cooking methods such as boiling or braising do not increase HCA and PAH levels (Ward et al., 1997). Therefore the temperature at which products are cooked may significantly increase the risk of ingesting these mutagenic compounds. According to Sinha et al. (2005) the intake of meat was not associated with an increased risk of cancer, however, the meat cooked at high temperatures was associated with increased colorectal cancer risk (p. 8034). Boiling, baking, and roasting may be the safest and best alternative one has should they continue the practice of consuming animal flesh to reduce the intake of HCAs and PAHs.

Puangsombat et al. (2012) recommend purchasing chicken with the skin on, baking chicken with the skin on and removing the skin prior to eating to further reduce the risk of HCAs exposure (p. 745). Other ways to reduce the risk of consuming these mutagenic compounds, HCAs and PAHs, include consuming rare to medium rare steak, fried pork patty, or baked beef. The NCI (2015) also recognizes that cooking meat in a microwave oven can reduce the amount of time cooking over high heat, they also recommend not using meat drippings to make gravies thus further reducing exposure to these mutagenic compounds, HCAs and PAHs (para. 12).

Cooking meat outside of the home can substantially decrease the risk of inhaling HCAs and PAHs which studies have shown are linked to lung cancer and might be hazardous to fetal development in pregnant women. Grilling meat outside and away from the homes ventilation unit can decrease the risk of inhalation of HCAs and PAHs. Stepping away from the grill when cooking to increasing ventilation and decreases exposure to these harmful mutagenic compounds. According to the NCI (2015) “HCAs are not found in significant amounts in foods other than meat cooked at high temperatures. PAHs can be found in other charred foods, as well as in cigarette smoke and car exhaust fumes” (para. 3). Therefore it is recommend to tend the grill at all times to ensure cooked meat is relatively char free, however to decrease the risk of consuming these mutagenic compounds as much as possible, limiting or stopping the consumption of grilled animal flesh, as well as stopping smoking and avoiding car exhaust are all things each and everyone of us has the ability to do.

Three of the biggest thing and individual can do to decrease the risk of consuming these mutagenic/possibly carcinogenic compounds associated with the ingestion of HCAs and PAHs in regards to cooked animal flesh is to:

  1. Avoid consuming all grilled animal flesh.
  2. Consume boiled or braised meat. Avoid cooking these products over open flames and/or pan frying.
  3. Limit or decrease the exposure to fumes from open flame barbecues and grills, especially for pregnant women to reduce the risk of potential complications during fetal development in utero.

The goal is to eliminate the risk of developing cancer. Therefore, avoiding all grilled/cooked animal flesh is best. Vegetarians tend to have little to no exposure to these harmful carcinogens as research indicates via studies conducted on hair, urine, and breast milk. While HCAs and PAHs are potent mutagenic compounds that increase our risk of developing a variety of cancers, consuming more plant based foods, with the aim of following a primarily whole foods plant-based diet significantly decrease exposure to these risks. Consuming significant amounts of HCAs and PAHs in cooked animal flesh increases the risk of developing cancer, therefore avoiding or severely decreasing the consumption of grilled/cooked animal flesh decreases the risk of ingesting these toxic substances which have mutagenic or cancer causing effects. The more plant-based our diet becomes, the less risk we have of developing the cancers associated with these substances.

Avoiding all animal flesh and animal by products will substantially decrease the risk of developing cancer through the ingestion of HCAs and PAHs but subsequently this also decreases the risk of heart disease as well due to limiting the consumption of saturated fat, cholesterol, and trans fats found in these products. While this is not the only way to decrease the risk of developing cancer, these avoidance measures will decrease the chances of developing cancer through the ingestion of HCAs and PAHs.

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