Does cooking food release toxins and carcinogens?
The short answer is “yes,” based on numerous government studies around the world (including the U.S. CDC, NIH, EPA, etc.), but only if you cook at higher-than-steaming/boiling temperatures. Studies indicate probable links between cancer rates and food fried/grilled at high temperatures (see below).
Thus if you’re serious about maintaining good health, you may want to reduce high-temperature cooked foods in your diet. It doesn’t mean you have to avoid such foods entirely, because your body can detoxify itself to some extent, via organs like the liver. But the less you abuse your body, the greater your chance of having a healthy life and old age.
There are four common ways to get carcinogens in your diet:
1. Heterocyclic amines (HCAs). High-temperature cooking of meat (beef, pork, chicken, fish, etc.) creates compounds known to cause cancer in laboratory animal tests. The higher the temperature, the worse the problem, especially above 300 degrees Fahrenheit (149C).
2. Polycyclic aromatic hydrocarbons (PAHs). Grilling on an open flame or smoking meat creates known carcinogens.
3. Acrylamide is the vegetarian counterpart to HCAs. High-temperature cooking of potatoes, grains (e.g., toast, cereal), and coffee are known to produce this cancer-causing substance.
4. Exceeding the smoke point of a cooking oil means the oil breaks down and starts to release carcinogens.
You can avoid these carcinogens by:
- Cooking more slowly, at a lower temperature (e.g., boiling, steaming, braising, and low-temperature frying). Avoid roasting, baking, grilling, high-temperature frying, or other high-temperature cooking methods. This doesn’t mean you can’t splurge once in a while.
- Using natural gas or propane instead of charcoal for grilling; gas/propane are cleaner-burning
- Cleaning your grill of charred bits first.
- Microwaving hunks of meat for a minute in the microwave before putting them on the grill, to reduce the time of exposure to high heat.
- Avoiding obviously charred pieces of meat. Cut them off.
- Avoiding overcooking food (the browner/more charred your toast/fries/meat, the more acrylamide or HCAs).
- Eating more vegetables and fruits and less meat, grains, or tubers.
- Keeping temperatures below the smoke point of your cooking oil.
- Using cookware that spreads heat evenly, so that you don’t have a hotspot overheating the center of the pan just because you needed to crank up the burner to increase the temperature at the edge of the pan.
- Avoiding coffee, since roasting coffee beans creates acrylamide.
The long answer:
We’ll go in order, from HCAs and PAHs to acrylamide and overheating cooking oil:
1. HCAs.
According to the National Cancer Institute (part of the U.S. National Institutes of Health), Heterocyclic amines (HCAs) are chemicals formed when muscle meat (beef, pork, chicken, fish, etc.) is cooked at high temperatures. 1
How this happens:
Proteins are made out of amino acids. Creatine is also made out of amino acids and is found in muscle tissue.2 At high temperatures, amino acids, creatine, and sugars react to form HCAs.
Laboratory rodents exposed to very high levels of HCAs (equivalent to thousands of times an adult human’s normal dietary exposure to HCAs) develop tumors in the breast, colon, liver, skin, lung, prostate, and other organs, in addition to full-blown cancers. Although adult humans may consume a lot less in HCAs per meal, the concern is that if a lot of HCA exposure over a short period of time causes cancer, then a little HCA exposure over a long period of time may also cause cancer.
Furthermore, Scientists have linked diets high in well-done, fried, or barbecued meat with colorectal, pancreatic, and prostate cancer.3 These links weren’t strong enough for the government to issue guidelines limiting consumption of red meat and smoked foods, and I’m sure that the meat and seafood lobbyists have done their part to ensure that things stay that way.
2. PAHs.
The incomplete combustion of organic matter creates polycyclic aromatic hydrocarbons (PAHs).4 PAHs have effects such as gastrointestinal, lung, skin, and bladder cancers; accordingly, various U.S. federal agencies such as the Department of Health and Human Services and EPA classify several PAHs as carcinogens, and the International Agency for Research on Cancer identifies several PAHs as “possibly” or “probably” “carcinogenic to humans.”5
PAHs are present in the environment due to natural and artificial sources such as: forest and grass fires, oil seeps, volcanoes, power plant emissions, internal combustion engine emissions (e.g., cars, trucks), asphalt production, and incinerator emissions.
To some extent you can’t avoid PAH exposure; even raw vegetables can be coated with some detectable amount of PAHs. That said, diet is the major source of human exposure to PAHs, and the major dietary sources of PAHs are grains and potatoes, as well as meat cooked over open flames.6 Vegetables and fruits do not have as much of a PAH problem as grains and tubers.
Processed/smoked/cured food can lead to higher PAH exposure. Grilling on an open flame can also lead to PAH exposure. For example, when grilling meat, fat and juices can drip into the fire, which partially burn up. The resulting smoke can deposit carcinogenic PAHs onto the meat surface. For similar reasons, smoked foods may also contain PAHs.7 Therefore, it would be advisable to reduce consumption of processed/smoked/cured meat and grilled foods in general.
3. Acrylamide.
High-temperature cooking causes problems with plant-based foods, especially potatoes, grains, and coffee. Sugars and asparagine (an amino acid) react to form acrylamide.8 It doesn’t matter if you cook organic vs. non-organic produce; these are naturally-occurring chemicals. At high doses (1000 times more than in a normal adult human diet), acrylamide has been shown to cause cancer in laboratory rodents.9 Although adult humans may consume a lot less acrylamide per meal, the concern is that if a lot of acrylamide over a short period of time causes cancer, then a little acrylamide over a long period of time may also cause cancer.
The International Agency for Research on Cancer classifies acrylamide as a probable human carcinogen; the US federal government agencies classify acrylamide as reasonably anticipated to be a human carcinogen.10 The European Chemical Agency listed acrylamide as a “substance of very high concern” in 2010.11
Acrylamide formation in foods like toast, potato chips, and French fries can start as low as 120C (248F), but cooking meat, seafood, and dairy products at high temperatures does not produce much acrylamide.12
4. Cooking oil heated beyond the smoke point.
Before we discuss smoke points, let’s talk about unrefined vs. refined oils.
Unrefined oils are made by crushing vegetable matter at relatively low temperatures and pressures via mechanical means. Refined oils often use harsh chemicals like hexane solvent that are then mostly filtered out, often at higher temperatures and pressures–but trace amounts remain. You won’t die from trace amounts of such harsh chemicals, because your body can detoxify itself to some extent, but I understand why some people seek to avoid refined oils in general–why make your body work harder than it has to?
Okay now let’s talk smoke points.
All cooking oils have a smoke point: the temperature at which they begin to chemically decompose and give off potentially carcinogenic free radicals. Obviously you want to stay below the smoke point. But what are the smoke points of various oils? Everyone has a different answer. That’s because there is no single answer!
Take olive oil for instance. First of all, many producers play games with purity and sell less-than-100%-extra-virgin olive oil as if it were 100% extra virgin olive oil. Second, there is variation among genuine extra virgin olive oils. Not every olive oil is alike, and they are definitely not all grown on the same tree. Nor are they all refined the same way (and actually extra virgin olive oil isn’t supposed to be much refined at all, other than filtering out solids). The result is that extra virgin olive oil might have a smoke point of 325F to 375F, roughly speaking. Only highly refined olive oils (subjected to high temperature/pressure and possibly chemical treatment), with flavor and color and impurities stripped out, have high smoke points.
This is why extra-virgin olive oil at 325-375F is considered low among cooking oils. According to Professor Wolke, butter is in the same boat: regular butter starts to break down at no more than 300F, although clarified butter (ghee) has a higher smoke point of about 450F–and is also not as good for your health, being the butter equivalent of “light” (highly refined) olive oil.
Sometimes rumors get spread that are incorrect, like how olive oil should never be used for cooking. In fact, olive oil breaks down about the same as any other oil and maybe even better.13 What probably happened is that someone read that extra-virgin olive oil has a relatively low smoke point (true) and concluded that ANY amount of heat applied to olive oil would create lots of toxins (false).
Also note that you want to use a cooking oil low in polyunsaturated fats because they break down and form aldehydes and other toxins at ~350F–even if they haven’t reached their smoke points yet.
For more information about what cooking oils are best to cook with, please see this article.
CONCLUSION:
High temperatures produce Maillard reactions (also known as “browning,” Maillard reactions are when amino acids and sugars react to make tasty flavors and nice-smelling aromas such as the flavor/aroma of cooked meat, toast, and other foods), but if you go too high, you produce carcinogens. The trick is to stay in a temperature range from about 140 C to 180 C (284 F to 356 F). You still will get plenty of browning at those temperatures, and you will avoid creating carcinogens that form at higher temperatures.
I’m going to end this post like how I began it: with a quick guide on how you can avoid these carcinogens by:
- Cooking more slowly, at a lower temperature (e.g., boiling, steaming, braising, and low-temperature frying). Avoid roasting, baking, grilling, high-temperature frying, or other high-temperature cooking methods. This doesn’t mean you can’t splurge once in a while.
- Using natural gas or propane instead of charcoal for grilling; gas/propane are cleaner-burning
- Cleaning your grill of charred bits first.
- Microwaving hunks of meat for a minute in the microwave before putting them on the grill, to reduce the time of exposure to high heat.
- Avoiding obviously charred pieces of meat. Cut them off.
- Avoiding overcooking food (the browner/more charred your toast/fries/meat, the more acrylamide or HCAs).
- Eating more vegetables and fruits and less meat, grains, or tubers.
- Keeping temperatures below the smoke point of your cooking oil.
- Using cookware that spreads heat evenly, so that you don’t have a hotspot overheating the center of the pan just because you needed to crank up the burner to increase the temperature at the edge of the pan.
- Avoiding coffee, since roasting coffee beans creates acrylamide.
FOOTNOTES