Why Deep Fried Foods May Cause Cancer

Cancer Risk from French fries
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In the latest study on dietary patterns and breast cancer risk among women, healthier eating was associated with eliminating three-quarters of the odds of breast cancer, whereas less healthy eating was associated with up to nearly eight times the odds. Included in the unhealthy eating pattern was the consumption of deep-fried foods, which have previously been linked to breast cancer, pancreatic cancer, lung cancer, oral and throat cancers, esophageal cancer, and cancer of the voicebox. No deep fried foods? What’s a Southern belle to do? Instead of deep fried foods, how about the traditional Southern diet, characterized by high intakes of cooked greens, beans, legumes, cabbage, sweet potatoes and cornbread, which may reduce the risk of invasive breast cancer significantly.

What about the consumption of deep-fried foods and risk of prostate cancer? Researchers at the Fred Hutchinson Cancer Research Center and the University of Washington found that eating French fries, fried chicken, fried fish, and doughnuts was associated with about a third greater odds of prostate cancer. After stratifying for tumor aggressiveness, they found slightly stronger associations with more aggressive disease, suggesting that regular intake of deep-fried foods may contribute to the progression of prostate cancer as well.

What in deep fried foods is so bad for us? Just heating oil that hot can generate potentially carcinogenic compounds, and then known carcinogens such as heterocyclic amines and polycyclic aromatic hydrocarbons form when the muscles of chickens and fish are cooked at that temperature. Deep-fried plants, on the other hand, can form acrylamide.

I did a video about acrylamide back in 2008, suggesting it’s a probable human carcinogen (See Acrylamide in French Fries). Since then, studies have suggested pregnant women may want to cut back on French fries to protect the growth of their baby’s body and brain. Based on a study (highlighted in my video, Cancer Risk from French Fries) feeding people a little bag of potato chips every day for a month, it now seems acrylamide may also cause inflammation as well, which could explain its purported role in cancer progression.

Acrylamide intake has been associated with endometrial cancer, ovarian cancer, lung cancer, kidney cancer, and esophageal cancer. How much cancer risk are we talking about? Taiwanese researchers examined lifetime cancer risk and French fry consumption. The researchers picked on French fries because they comprise by far the greatest percentage contribution of acrylamide to the diets of children. They estimated that, at most, one or two boys and girls out of every ten thousand would develop cancer eating French fries that they would otherwise not have developed if they hadn’t eaten French fries. So it’s not as bad as eating something like fried fish, or fried chicken, but how much is that saying?

The level of cancer risk in both boys and girls associated with French fries depends on how long and hot they’re fried. In Europe, the food industry swore that they’d self-regulate and control fry times to decrease acrylamide levels, but we’ve yet to see any subsequent change in acrylamide levels in French fries.

Researchers continue to urge that the cooking temperature should be as low as possible and the cooking time should be as short as possible, “while still maintaining a tasty quality” of course. We wouldn’t want to reduce cancer risk too much—they might not taste as good!

Blanching the potatoes first reduces acrylamide formation, but potato chip companies complain that, not only would it muck with the flavor, but it would reduce the nutritional properties by leaching away some of the vitamin C. But if we’re relying on potato chips to get our vitamin C, acrylamide is probably the least of our worries.

More on heterocyclic amines:

There are some things we can do to counteract the effects of these carcinogens, though:

I touch on polycyclic aromatic hydrocarbons in Meat Fumes: Dietary Secondhand Smoke and Is Liquid Smoke Flavoring Carcinogenic?
Certain fats may play a role in breast cancer survival as well: Breast Cancer Survival, Butterfat, and Chicken and Breast Cancer Survival and Trans Fat.

-Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.

Image Credit: Kim Love / Flickr

  • Julie

    Even before the oil gets in the fryer, it’s been heavily damaged by the refining process. The multi-step process to take a whole food seed to a refined oil leaves behind oxidized, reactive fatty acids and chemical residues.

    • guest

      Does this refining process oxidize vegan DHA pills, making these fats harmful?

      • Julie

        I hope not. Great question!

      • guest

        Of the well known dietary fatty acids, DHA has the highest peroxidation index. Do the manufactures add an antioxidant to their DHA products?

        • Joseph Gonzales R.D.

          Agreed, great question! It may be more of a question for the manufacturer. We do know that DHA oil from algae appear effective. Another study here.

          • Leslie

            Yes, but does the DHA vegan supplement also provide EPA, or just DHA? This is important, no? I’ve seen most vegan DHA supplements make no mention of the product containing EPA.
            Fish oil has both. Maybe you can clear this up for me, I assume I am missing something here in the understanding.

          • Thea

            Leslie: I’ve seen quite a few commercial, algea-based omega three pills which include both DHA and EPA. Here’s just one example (not one I’m promoting. Just the first one that popped up in a random search):
            http://www.devanutrition.com/vegan-dha-epa-delayed-release-omega-3.html

            I’m sure there are also pills with just the DHA, but I don’t think it is hard to find ones with the EPA too if that’s what you want.

          • Leslie

            How is it that some algae provide both DHA and EPA, and others do not? I figured that algae in itself ALWAYS contained both the DHA and EPA, as fish oil contains both DHA and EPA and the fish get it from eating algae. But some vegan companies say just DHA. Hmmmm….

          • Thea

            Leslie: I had assumed that the difference between different pill claims was due to different processing techniques. But you could be right. It could be that the pills which only claim to have DHA are simply not reporting the EPA? I really have no clue.

          • guest

            Hi Leslie: Most algal DHA supplements contain only DHA. Increasingly though there’re products with both DHA and EPA. If you type in “vegan omega-3” on amazon, you can find them, but they are even more expensive than algal DHA-only products. It’s, of course, good to take both DHA and EPA but not essential because DHA and EPA equilibrate in the body: If you took only DHA, some of it would be converted to EPA, and vice versa.

          • Leslie

            I find it thought provoking that the fish oil companies are shifting to balancing their DHA EPA supplement to contain more EPA than DHA, as a greater amount of EPA than DHA in the body has been found to be more effective for mood issues, as well as some feel other issues as well. Vegans may be compromising themselves by taking DHA only….creating a level of DHA and EPA that might adversely effect them.

            http://www.nutraingredients-usa.com/Research/EPA-stands-alone-as-a-depression-fighter

            https://labdoor.com/article/epa-to-dha-ratio-a-benefits-and-risks-analysis

          • Joseph Gonzales R.D.

            Some use ratios including EPA and DHA. Other are just DHA.

        • ron

          Seems like a good question for one of the manufacturers like Nordic.

  • charles grashow

    From the study you linked to

    http://www.ncbi.nlm.nih.gov/pubmed/23651876
    Dietary patterns and breast cancer risk among women.

    “The ‘healthy’ food pattern was characterized by the consumption of vegetables, fruits, low-fat dairy products, legumes, olive and vegetable oils, fish, condiments, organ meat, poultry, pickles, soya and whole grains; while the ‘unhealthy’ food pattern was characterized by the consumption of soft drinks, sugars, tea and coffee, French fries and potato chips, salt, sweets and desserts, hydrogenated fats, nuts, industrial juice, refined grains, and red and processed meat.”

    SO – the “healthy food pattern” included low fat dairy, olive and vegetable oils, organ meat and poultry”!!

    • Matt

      and excluded tea!?!

      • largelytrue

        This study exemplifies the importance of the ability to read the study and understand the statistical method in order to interpret the study correctly. They did what is known as principal component analysis (https://en.wikipedia.org/wiki/Principal_component_analysis ) as their factor analytic technique. The goal was dimension reduction prior to statistical analysis, not a direct inference of a best-fit ‘healthy’ pattern and a best fit ‘unhealthy’ pattern — really this would make no sense for a two-factor model since the unhealthiest pattern would be simply the negative of the healthiest pattern and there would only be one factor.

        The correct interpretation of their statistics is that:
        1) They first found two orthogonal factors which varied significantly in their sample. That is, there is ‘A-type’ variation in which consumption of vegetables, fruits, low-fat dairy, etc, all increase together, and some of the other dietary components decrease. Then there is ‘B-type’ variation in which consumption of soft drinks, sugars, tea, etc all increase together, and some other dietary components decrease. The sample diets from the FFQ varied from person to person a fair bit in both the A-way and the B-way. The study calls them ‘healthy’ and ‘unhealthy’ but based on the characteristics given they could also plausibly be called ‘traditional/rural’ and ‘urban/industrial’.
        2) In a model that looked at both A-ness and B-ness of diets as independent variables, A-ness was found to associate with higher breast cancer risk while B-ness was found to associate with lower risk. If you had to pick between A-ness and B-ness as the only ways in which you could vary your diet to protect yourself from breast cancer, your best bet would be to reduce B and increase A. That said, A and B cannot be interpreted simply as straightforward lists of healthy/unhealthy things. In fact there are very obvious reasons why tea consumption would tend to increase along with all the other refined and processed foods, that have nothing to do with tea’s health per se. There are also obvious reasons why organ meats might be more common among people with greater access to other fresh and traditional foods, that have nothing to do with the health of organ meats per se.

        If you had to ask me the study is valuable but it doesn’t do much to pinpoint exactly what is good or bad for breast cancer. We rely on other research in order to interpret what the healthiest dietary pattern for preventing breast cancer might be. Note that in Greger’s article the study in question is only introduced as the latest, not the greatest. In many respects, the study isn’t all that great.

        • charles grashow

          This is what Dr Greger said – “healthier eating was associated with eliminating three-quarters of the odds of breast cancer, whereas less healthy eating was associated with up to nearly eight times the odds”

          Again – the healthier eating pattern included vegetables, fruits, low-fat dairy products, legumes, olive and vegetable oils, fish, condiments, organ meat, poultry, pickles, soya and whole grains.

          No matter how you want to spin it you can’t.

          However it would be useful if the good doctor would post a link to the ENTIRE study not just the abstract.

          • largelytrue

            The study is freely accessible, Charles, and can be reached from the source link to the publisher on Greger’s PubMed citation. Greger is quoting his results from table 3, model II. I should mention that I misspoke a bit in calling these models ‘univariate’. They focus on only one pattern at a time as the independent variable of interest, but their other statistical controls such as age, menopausal status, etc, are independent variables also. Note that I haven’t said anything about the quality of Greger’s reporting on the study yet, either. Given that your OP talked about the study and not what Greger said, I assumed we were talking about what the study itself means.

            Read the study and try to comprehend what I wrote as something other than ‘spin’, then I might get back to you. I assure you that they found two patterns which spanned about 24-31% of dietary variation in the population, then asked how healthy those patterns actually were. They did not ask up front “what is the pattern whose variation explains the greatest variation in health outcomes?”. The latter form of questioning is well-framed to get you a list that distinguishes apparently healthy foods from apparently unhealthy, while the former is not.

          • charles grashow

            The abstract is available not the full study. If you have a link to the full study could you post it here.

          • largelytrue

            When you get to the journal’s front page with the abstract, you then select the format that you want in order to get to the article itself. This is standard procedure for almost all scientific journals, although of course it isn’t generally the case that the article will prove to be open access when you try to do this. Public Health Nutrition is not exactly doing a great job of showing whether an article is open access on the article’s main page, either.

            Here’s a link to the html format: http://journals.cambridge.org/action/displayFulltext?type=6&fid=9218570&jid=PHN&volumeId=17&issueId=05&aid=9218569&bodyId=&membershipNumber=&societyETOCSession=&fulltextType=RA&fileId=S1368980013001018

      • largelytrue

        This study exemplifies the importance of the ability to read the study and understand the statistical method in order to interpret the study correctly. They did what is known as principal component analysis (https://en.wikipedia.org/wiki/Principal_component_analysis ) as their factor analytic technique. The goal was dimension reduction prior to statistical analysis, not a direct inference of a best-fit ‘healthy’ pattern and a best fit ‘unhealthy’ pattern — really this would make no sense for a two-factor model since the unhealthiest pattern would be simply the negative of the healthiest pattern and there would only be one factor.

        The correct interpretation of their statistics is that:
        1) They first found two orthogonal factors which varied significantly in their sample. That is, there is ‘A-type’ variation in which consumption of vegetables, fruits, low-fat dairy, etc, all increase together, and some of the other dietary components decrease. Then there is ‘B-type’ variation in which consumption of soft drinks, sugars, tea, etc all increase together, and some other dietary components decrease. The sample diets from the FFQ varied from person to person a fair bit in both the A-way and the B-way. The study calls them ‘healthy’ and ‘unhealthy’ but based on the characteristics given they could also plausibly be called ‘traditional/rural’ and ‘urban/industrial’.
        2) In a model that looked at both A-ness and B-ness of diets as independent variables, A-ness was found to associate with higher breast cancer risk while B-ness was found to associate with lower risk. If you had to pick between A-ness and B-ness as the only ways in which you could vary your diet to protect yourself from breast cancer, your best bet would be to reduce B and increase A. That said, A and B cannot be interpreted simply as straightforward lists of healthy/unhealthy things. In fact there are very obvious reasons why tea consumption would tend to increase along with all the other refined and processed foods, that have nothing to do with tea’s health per se. There are also obvious reasons why organ meats might be more common among people with greater access to other fresh and traditional foods, that have nothing to do with the health of organ meats per se.

        If you had to ask me the study is valuable but it doesn’t do much to pinpoint exactly what is good or bad for breast cancer. We rely on other research in order to interpret what the healthiest dietary pattern for preventing breast cancer might be. Note that in Greger’s article the study in question is only introduced as the latest, not the greatest. In many respects, the study isn’t all that great.

  • marcel

    A litttle more nuancing might help.
    I obtain lots of vegetable from my grocery garden, wich I store in my freezer for winter time, after boiling it for a short minute.
    I may hope that that is not so bad!

    • george

      As I understand, boiling in water and steaming don’t cause acrylamide formation. It’s the burning of plant foods due to dry heating that leads to acrylamide.

  • Thanks!
    The issue for me with FAT supplementation is this;

    Many Many people arer taking all kinds of Omega’s, Olive, Primrose oils etc. Can we clarify the research as to how they oxidize and cause damage? They layman really has no idea on how to proceed and not create chaos with the oils they take. Now Dr Peter Glidden is against all oils for the most part. I think he makes an exception for Youngevity EFA and maybe coconut oils. Any help to clarify would go a long way.

    • Joseph Gonzales R.D.

      Great point, Anthony. A guest below also had a comment about oxidation. Maybe this can be another NutritionFacts Research Fund project? Dr. Greger has a video about the true shelf life of cooking oils. It would be nice to see more on the oils you mention.

    • Leslie

      So would fried coconut oil be safe, and organic potato chips fried in just organic coconut oil not be an issue/problem, as far as arrylamide content as well as oxidation, inflammation? Wondering what you think about this. I have no idea.

      • Frankly I am leaning very strongly towards stopping any supplemental oils. I prefer to get them from whole foods anyway like avocado, sardines etc. The evidence is starting to pile up against the oxidation of oils and the constant hemmoraging of free radicals. Remember that heat will always increase the rate of oxidation.

        • guest

          High arsenic levels in sardines, from the data I have seen.

  • Jan

    is it safe to bake potatoes, etc. in the oven brushed with a little olive oil? What is the temperature at which acrylamide formation becomes a concern?

    • Joseph Gonzales R.D.

      Hi Jan. Here is a video about the best way to cook sweet potatoes. It’s really the french fries (deep frying) that is problematic, as they are laden with acrylamide. Here is a study looking at acrylamide and temperature. This study mentions how cooking time and temperature may determine acrylamide levels.

      • I watched that video & I like the fact that Dr. Greger won’t compromise quantity of GOOD FOOD vs. quality.. He mentions that best way of eating such a healthy food as sweet potato is how you get most of it.. Therefore if someone doesn’t have time or facility to boil, they don’t have to stop eating it! one can bake & eat more of it to get same nutrients. That obviously doesn’t apply to french fries, but reminds me about some schools or work places, which only provide students/employees with french fries & no better alternative. Here the challenge is either eat the deep fried potatoes or stay hungry.. This is a much more difficult decision to make, and for me as an advocate for public health is an example of how important is infrastructure changes to have healthier nation.

  • Good information. I will be sharing the information

  • I will be lurking around the net trying to find out about the dangers of oxidation of oils. If anyone else finds anything please post.

  • Matt

    beast carcinogen indeed

  • Snm6Y

    How about air popped popcorn? Hot temperature? Starch? Short cooking time? Sounds like a recipe for acrylamide. I would be bummed…I love my air popped popcorn.

    • Joseph Gonzales R.D.

      Great question, especially because I tend to eat air-popped popcorn like a mad man! One study I found tested microwaved popcorn finding it safe. Another study listed popcorn as low in acrylamide. Considering popcorn is a whole grain and loaded with fiber and antioxidants I still think air-popped is fine and acrylamide is of little concern.

  • Fred

    The August 2015 LEF magazine has a listing for AGEs (advanced glycation end products) per serving for various foods. Worst is fried bacon at 11,905.

  • Mick

    Acrylamide is one thing, AGEs is another, but there is one other thing even worse than acrylamide, called PhIP. This one is formed in meat in a reaction between creatine and creatinine (so technically it’s not an AGE, I think) in high temperatures. This one probably deserves attention and a video, as if meat already wasn’t bad enough for us…