Carcinogens in Meat

HCAs and PAHs are two common carcinogens. About 10% carry an increased genetic sensitivity.

HCAs and PAHs are environmental pollutants associated with adverse health outcomes, including cancer, asthma, and reduced fertility. These chemicals are commonly found in smoke-polluted air, as well as in our diet.

HCA's (heterocyclic amines) are formed when cooking meat at a high temperatures. PAHs (Polycyclic Aromatic Hydrocarbons) can also found in meat, mostly when grilled over an open flame, a hot surface, or smoked.

Routes of exposure

Exposure to PAHs and HCA's is common both by breathing and by diet. PAH and HCA originate from burning wood and fuel for homes and in gasoline and diesel exhaust, cigar and cigarette smoke. 
PAH and HCA are also commonly found in smoked, barbecued, or charcoal-broiled foods, roasted coffees, and sausages. These chemicals are created as a result of cooking components of meat -amino acids, sugar, and creatine, at high temperatures (typically above 300°F). The amount of HCAs produced may depend on how long the meat is exposed to those high temperatures. Grill over an open flame and smoking meat yields higher levels of the carcinogens.

Metabolism

The UGT1A1 is an enzyme responsible for the detoxification and elimination of PAH and HCA. It is also responsible for the metabolism of bilirubin, a normal break-down product of old blood cells.

Increased serum bilirubin concentrations are usually a sign for genetic sensitivity to the PAH and HCA carcinogens. Increase bilirubin levels are mostly due to genetic variations in the UGT1A1 enzyme, resulting in what is known as Gilbert’s syndrome. This is a quite common and mostly harmless syndrome that results from UGT1A1 low activity levels. Individuals with Gilbert’s syndrome have fluctuating bilirubin levels, which are often within the standard range. Illness, stress, or fasting can precipitate a rise in bilirubin levels, leading to hyperbilirubinemia and symptoms such as temporary jaundice or abdominal discomfort. However, these symptoms will typically resolve themselves, and again- the syndrome is harmless in adults.

Genetics

Variant forms of UGT1A1 are quite common. The UGT1A1*28 polymorphism affects about 8%-10% of Caucasian and African-American populations, while the UGT1A1*6 affects 2-5% of East-Asians. Both variants reduce UGT1A1 expression by about 30%, compared to the activity of the enzyme in an average healthy average individual. 

Individuals homozygous for this allele (carry two copies of the TA7 variant form) have an enzymatic activity at ~30% of normal and can present with Gilbert’s syndrome. Increased bilirubin levels are common among such individuals, as can be seen below.

Kringen MK, Piehler AP, Grimholt RM, Opdal MS, Haug KB, Urdal P. Serum bilirubin concentration in healthy adult North-Europeans is strictly controlled by the UGT1A1 TA-repeat variants. PLoS One. 2014 Feb 28;9(2):e90248.

Health effects

UGT1A1 enzymes have been seen to metabolize carcinogens like benzo-pyrenes, PhIP, PAHs and HCAs, as well as estradiol, another potential carcinogen.

Reduced UGT1A1 activity has been shown to increase the risk of developing colorectal and breast cancer across multiple studies in Chinese and White populations.

How to reduce the risk  

Changes in life-style and diet can markedly reduce exposure to these chemicals.

Individuals with an added genetic risk may go vegetarian or consider eating less meat- its especially healthy for people like you. Two to three servings a week should maintain your dietary needs and keep your risk levels low. Cooking in a temperature lower than 300°F can reduce your exposure to the carcinogens. Grilled, barbecued, smoked meat and sausages should be avoided.
 

Roasted coffee and black tea also contain high levels of PAH's. Choose high-quality, fresh coffee for reduced exposure.


Exposure to PAH's and HCA's through breathing is common. Quit smoking. Average smokers take in about 10 times more benzene than nonsmokers each day. Passive second hand smokers are also at risk.
Avoid as much as you can breathing gasoline and diesel exhaust, open fires and incinerators.

The good news are that you can help your body deal with the chemicals by eating cruciferous vegetables. These vegetables increase the production of the UGT1A1 enzyme, both in sensitive and non-sensitive individuals.  It is recommended to eat more cauliflower, cabbage, kale, garden cress, bok choy, broccoli and Brussels sprouts, especially when eating meat.