Cooking without Fire
While an exact date remains elusive, around a million years ago humans began using fire to cook their food.1 The benefits were plenty. The heat from fire provided a method of destroying potentially harmful microorganisms within meats and vegetables. Perhaps more importantly, cooking with fire left food more absorbable, thus humans were able to quickly consume and digest foods that would normally take hours to ingest. Such a benefit left the monkeys to hours of chewing and allowed humans to engage in hunting, playing, and sleeping.
While the benefits of cooking are plenty, playing with fire comes with its risks. Excessive heat, burning, and physical damage turn food from healthy to potentially dangerous. Burnt food contains several products called hydrocarbons that can lead to cancer-promoting damage to our cells. In response to this damage, several detoxification pathways are activated, like CYP1A2 N-acetyltransferase 1 (NAT1) and 2 (NAT2). However, these pathways are not always successful in offsetting the potential damage and they have been associated with a multitude of cancers,2 with colon cancer as the most commonly discussed.3
Heterocyclic aromatic amines (HAA) and polycyclic aromatic hydrocarbons (PAH) are formed when food is heated or processed. PAH are found in petroleum and coal along with products derived from them.4 Using wood or charcoal to smoke foods leaves then with detectable amounts of benzo[a]pyrene and other PAH. Sausages burned over wood contain up to 200 parts per billion (ppb) benzo[a]pyrene, while charcoal-cooked meats contain up to 50 μg/kg.
Leaner meets have less amounts of PAH than less than fatty cuts of meat likely due to fat dripping onto the charcoal and fire to enhance burning of the meat. Smoked fish, while lean, appears to have significant levels of HAAs.5
As a side, vegetable oils, which continue to be promoted by many as pillars of health, contain even higher concentrations of benzo[a]pyrene, likely from the significant heating and processing that they encounter during the processing and creation of oil from a vegetable or seed source that contains very little. Worse yet may be the canned sprays the often contain a hydrocarbon propellant along with a vegetable oil.
While meat seems to take the majority of the blame when it comes to hydrocarbons, other data reveal that the major dietary sources of PAHs are cereals and vegetables.6 Perhaps less surprising, a significant amount of genotoxic elements accompany grilled vegetables.7
Verdict: Avoid grilled and smoked meats and vegetables and direct fire cooking.
Into the Frying Pan and Out of the Fire
Pan cooking removes the direct fire and charcoal from the cooking process and replaces it with heating a fat source on a metal surface. Yet, we are not in the clear as high-heat cooking on a pan can still damage both the food and the cooking fat or oil. This does provide us with more control as fats with a more stable geometric structure, like saturated and minimally unsaturated fats, and those with a high smoke point can help mitigate this issue. This has been discussed before both here and in Misguided Medicine.
In a recent study, over 60 men and women consumed meat during two separate weeks that was pan-cooked at two different temperatures during each respective week.8 During the first week, meat was cooked at 100° and this was increased to 250° during the second week. Heterocyclic aromatic amines (HAAs) were measured in the meat after cooking. None was detected in the low temperature meat, while the meat exposed to 250° temperatures contained large amounts of HAA. CYP1A2 and NAT2 activity, both of which are induced from exposure to HAAs, were measured in the study participants. NAT2 was similar after both cooking periods, while CYP1A2 was significantly increased in 72% of participants after consumption of the higher temperature-cooked food.
Verdict: Avoid high heat pan cooking and instead let food simmer.
Advanced Glycation End Products
Advanced glycation endproducts (AGEs) are formed when glucose (sugar) reacts with fats and proteins through the Maillard reaction, named after its founder who noted a darkening of sugars when heated.9 After eaten, the AGEs can bind to cells in the body wreaking havoc. AGEs are responsible for many of the complications of diabetics as their chronically elevated levels of blood sugar leads to the formation of AGEs within the body, and these substances eventually collect in their organs, including the kidneys and eyes.10
The mechanism of AGE formation in food remains somewhat controversial, as while AGEs are the permanent linking of glucose to another substance, fattier foods may have higher amounts of AGEs after cooking.11 The good news is that methods to lower AGE content in food is similar as those used to lower hydrocarbons, including lower heat, moist cooking, and acidic marinades with vinegar or lemon juice.12
Verdict: Similar techniques to reduce hydrocarbon formation can be used to limit AGEs in our food.
Marinades and Health
Marinades have traditionally been used in cooking as a method to prepare meat and even vegetables prior to cooking. This generally involves soaking meats or vegetables in liquid containing enzymes to break down physical elements of the food to tenderize them or acids to tenderize and flavor them. These marinades typically contain lemon juice, vinegar, or alcohol along with some herbs and spices.
Marinades add flavor to our food and improve the texture, but little known is the fact that they also improve the nutrition of our foods by offsetting damage during cooking. Researchers have looked into the effect of marinades on PAH development during the grilling of meat. Seven marinades were tested, ranging from a basic marinade, including sugar, water, onion, turmeric, lemon grass, salt, garlic, coriander and cinnamon. Other marinades varied from oil and lemon juice, to spice mixtures. The researchers found that acidic marinades with lemon juice appeared to lower PAHs by about 70%. The duration of the marinade exposure did not affect PAH development. Overall, the beneficial effect from largest to smallest was: basic–lemon > basic > basic–oil–lemon > basic–oil.
Other data, published in the Italian Journal of Food Science no less, reveals that a wine marinade reduces PAH content by 86%.
Verdict: If you are going to cook or grill your meat or vegetables, marinade them first.
Combining Meat and Vegetables
Luckily, nature provided some other methods to offset the HAA that can accompany cooked meat. Cruciferous vegetables like broccoli and Brussels sprouts has been shown to offset the potential damage of HAA in studies.13 These vegetables enhance metabolism of the amines, reducing the exposure of our colorectal lining and cells to the potentially harmful HAA.
Good Cooking Practices:
1. Avoid grilling and open flame cooking
2. Avoid burning food
3. When cooking in the oven, use 350° as the maximum temperature
4. Use stable fats and oils that have a lesser propensity to become denatured or smoke when pan cooking
5. Avoid vegetable oils
6. Utilize steaming for vegetables
7. Avoid smoked foods or meats
8. Utilize cooking techniques that require low heat, like braising and stewing
9. When cooking on a pan use low heat
The benefits and risks of cooking meat must of course be a balance. Temperatures too low will leave harmful bacteria alive, especially in pork products. While exact data remains unclear, it appears the oven temperatures kept at a maximum of 350° may be the healthiest. Pan cooking should generally be left as low as possible to avoid burning or significant browning. Marinades may be a potent method to reduce the formation of cancerous compounds during cooking while adding elements of flavor to our food. However, we must remember that cooking techniques can largely affect the health attributes of our food and a burnt hotdog made with the meat from confined, grain-fed cows is hardly comparable to safely cooked meat from grass-fed, free-roaming cows.
1. Berna F, Goldberg P, Horwitz LK, et al. Microstratigraphic evidence of in situ fire in the Acheulean strata of Wonderwerk Cave, Northern Cape province, South Africa. Proc Natl Acad Sci U S A. 2012;109(20):E1215-E1220. doi:10.1073/pnas.1117620109.
2. Mastrangelo G, Fadda E, Marzia V. Polycyclic aromatic hydrocarbons and cancer in man. Environ Health Perspect. 1996;104(11):1166-1170. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1469515&tool=pmcentrez&rendertype=abstract. Accessed October 25, 2015.
3. Vineis P, McMichael A. Interplay between heterocyclic amines in cooked meat and metabolic phenotype in the etiology of colon cancer. Cancer Causes Control. 1996;7(4):479-486. http://www.ncbi.nlm.nih.gov/pubmed/8813437. Accessed October 25, 2015.
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6. Phillips DH. Polycyclic aromatic hydrocarbons in the diet. Mutat Res Toxicol Environ Mutagen. 1999;443(1-2):139-147. doi:10.1016/S1383-5742(99)00016-2.
7. Alomirah H, Al-Zenki S, Al-Hooti S, et al. Concentrations and dietary exposure to polycyclic aromatic hydrocarbons (PAHs) from grilled and smoked foods. Food Control. 2011;22(12):2028-2035. doi:10.1016/j.foodcont.2011.05.024.
8. Sinha R, Rothman N, Brown ED, et al. Pan-Fried Meat Containing High Levels of Heterocyclic Aromatic Amines but Low Levels of Polycyclic Aromatic Hydrocarbons Induces Cytochrome P4501A2 Activity in Humans. Cancer Res. 1994;54(23):6154-6159. http://cancerres.aacrjournals.org/content/54/23/6154. Accessed October 25, 2015.
9. Maillard LC. Action des acides amines sur les sucres; formation des melaniodines par voie methodique. C R AcadSci . 1912;154:66-68.
10. John WG, Lamb EJ. The Maillard or browning reaction in diabetes. Eye. 1993;7 ( Pt 2):230-237. http://www.ncbi.nlm.nih.gov/pubmed/7607341.
11. Uribarri J, Cai W, Sandu O, Peppa M, Goldberg T, Vlassara H. Diet-derived advanced glycation end products are major contributors to the body’s AGE pool and induce inflammation in healthy subjects. Ann N Y Acad Sci. 2005;1043:461-466. doi:10.1196/annals.1333.052.
12. Uribarri J, Woodruff S, Goodman S, et al. Advanced glycation end products in foods and a practical guide to their reduction in the diet. J Am Diet Assoc. 2010;110(6):911-916 e12. doi:10.1016/j.jada.2010.03.018.
13. Murray S. Effect of cruciferous vegetable consumption on heterocyclic aromatic amine metabolism in man. Carcinogenesis. 2001;22(9):1413-1420. doi:10.1093/carcin/22.9.1413.
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