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Good, Great, Bad, & Killer Fats

Avoiding trans fats doesn’t just mean staying away from junk food.

September 7, 2010 |
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Supplementary Info

Sources Cited



Not all fats are bad though, there are good fats.The monounsaturated fats in nuts and avocados. There are great fats. The Omega-3 fats in flax seeds. And then there are the bad fats, the saturated fats found primarily in meat and dairy. And finally, the killer fats, the trans fats which are found in only two places, hydrogenated oils and meat and dairy. Trans fats are basically only found in one place in nature, in animal fats. Now thanks to better living through chemistry though, the food industry found a way to create these toxic fats synthetically by hardening vegetable oil in a process called hydrogenation, which rearranges their atoms to make them behave more like animal fats. This may be good for shelf life, but not good for human life. The most prestigious scientific body in the United States, the National Academy of Sciences, released a damning report on trans fats and concluded that the only safe intake of trans fats was zero. The Academy said that the tolerable upper daily limit of intake was zero. If the National Academy of Sciences is saying the only safe intake of trans fats is zero, and about one fifth of American trans fat intake is coming from animal products. Did they recommend that everyone should only eat vegan? No they didn't, but why not? They were challenged on it and one of the authors of the report, a nutritional epidemiologist at the Harvard School of Public Health responded  "We can't tell people to stop eating all meat and all dairy products. Well, we could tell people to be vegetarians..." he added, "If we were truly basing this on science we would, but it is a bit extreme." Amazing. Wouldn't want scientists to base anything on science, would we?

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by veganmontreal.

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Dr. Michael Greger

Doctor's Note

Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out theother videos on fat. Also, there are 1,449 other subjects covered in the rest of my videos--please feel free to explore them as well!

  • Michael Greger M.D.

    Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the other videos on fat. Also, there are 1,449 other subjects covered in the rest of my videos–please feel free to explore them as well!

    • Joanne Irwin

      My program advocates low fat diets, avoiding all oils (we know those are bad!), and, eating nuts and seeds only in limited amounts. Some physicians state that they must be avoided totally. Research and other nutrition physicians state that nuts and seeds, eaten with other foods (as in salad dressings and smoothies), are necessary for proper absorption of important micronutrients. Consuming totally low fat foods can lead to impaired immune function. I’ve check the research, but would appreciate further input if you have any.

  • VegeMarian

    I’m dismayed that the author of the report effectively concedes that the science shows a vegan diet is best (with regard to trans fat intake) but he is unwilling to endorse it because it’s “a bit extreme.” The authors could help so many people by simply making recommendations consistent with their research. It shows just how strongly conditioned we are to eat animal products. It’s unfortunate that top scientists are no exception.

    • Karen A

      “ The authors could help so many people by simply making recommendations consistent with their research. It shows just how strongly conditioned we are to eat animal products. It’s unfortunate that top scientists are no exception.”


      And it’s seen as extreme because these people are not out there making sure that accurate information is being made mainstream. Vicious circle.

      • barbarabrussels

        First reactions I hear upon becoming whole food vegan, that’s a bit extreme! :-) I don’t argue, I’m happy, I just say ‘If you say so…’ I just hope my improved health (after just 2 weeks) will inspire them and some of it will sink in.

  • lbateman

    Yes, it’s so crazy … medical leaders can all be saying now ‘we all have no choice but to go vegan, and change is not that hard’, then watch out for the amazing health & enlightenment ahead.
    Meditation, reflection, reverence for science results, and ethical ways are the only worthwhile way.
    ~ A Vegan Nurse.

  • BPC

    I found a fascinating study (Innis and King, Am J Clin Nutr 1999;70:383–90; PMID=10479201) that provides compelling evidence that the breast milk of Canadians mothers contains up to 18.7% trans-fats (avg. was about 7%) and that these high concentrations are reflected in the blood concentrations of trans-fats of their breast-fed infants.

    Also possibly of relevance to this topic was the finding that approximately 20% of the trans-fats in the mother’s milk originated from dairy and meat sources, according to Table 4 of that paper.

  • br85
    “…Most importantly, however, the naturally occurring trans fats have not, as they occur in animal fats, been shown to share the harmful properties of the synthetic trans fat resulting from hydrogenation. This does not mean that all the trans fatty acids are in themselves harmless, but that any harmful effect is limited and balanced by the beneficial effects of, for example, trans isomers of conjugated linoleic acid (CLA) which are health-promoting with specific roles to play in our bodies. Also vaccenic acid, the main ‘natural’ trans fatty acid, can be metabolised by humans to CLA.”

    Sometimes it’s just not as simple as it seems, and there may, in fact, be a reason that people who eat junk food seem to suffer more than those who live on an almost all-meat diet. Science still seeks truth, but incomplete science is bad science, and unfortunately, should never be used to support a viewpoint we already had for unrelated reasons.

    • DrDons

      Unfortunately all science is incomplete as the science is continually changing…. sometimes leading us to a shift in our beliefs or paradigm and sometimes continuing to confirm our beliefs. I don’t believe science seeks the truth… only the best hypothesis given the science at the time. If we believe we have the “truth” we risk becoming trapped in our own belief system like “I need to consume animals to get quality protein” or consumption of foods high in protein is “good” or “milk does the body good”. I would say it is never simple as human nutrition is very complicated and worse these complicated processes occur in systems that are complex and adaptive. So we are stuck with developing beliefs that help us navigate the increasingly complex world. I think on balance current science supports the avoidance of trans fat whether synthetic or “natural”. I believe the best recommendation at this point is to avoid both animal products and processed foods(foods with labels). But keep tuned to as the science is constantly changing.

  • Heidi Woodruff

    I used something called “Copha” – ingredients Hydogenated coconut oil , soya bean lecithin in a vegan baked treat. Is this the killer “trans fat”?

    • Alexandra Georgiadis

      Hi Heidi,
      When oils are fully hydrogenated they contain almost no trans fats. They do however usually contain more saturated fat. These more solid fullly hydrogenated fats, although not the healthiest fat choice, are not the “killer” trans fats. It is the partially hydrogenated oils that you should stay away from; they contain the trans fats.
      Now to answer your question about Copha: I am not familiar with this product, but it is important to be aware that sometimes packages simply say “hydrogenated oils” and do not specify whether they are partially or fully hydrogenated, leaving the consumer unsure of whether it contains transfats. It might be a good idea to research this product to be sure that the coconut oil is fully hydrogenated. Another important thing to note is that companies can label their products “trans fat free” even when partially hydrogenated oils are listed in their ingredients. They get away with this because, under FDA regulation, if there is less than 0.5 grams of trans fats per serving than it can be deemed trans fat free. The problem here is not only that we are consuming traces of trans fats when we’re led to believe we are not consuming any, but we often eat more than 1 serving in one sitting; I know I do! I hope this helps.
      If you’re interested, here are some more links on fats and fat products/supplements:

      • Jo

        i emailed the Copha company they advised that it is 0.8g of trans fats per 100g, In Australia, (where Copha is from) there is no legal requirement to put trans fats on our nutrition labels

  • Toxins

    How come the Paper from the national academies of science also says that avoiding meat and dairy may cause inadequate protein intake. Why would they even mention this?

  • Ashish

    Here is a new interesting study: Trans fat consumption and aggression.

  • leena j dsouza

    i have a back problem some times it cathes vry hard i cant spear it

  • Len Brown

    I grind flax seed before cooking mixed bean dishes.
    Does cooking destroy the benefits of flax oil ?

    • Don Forrester MD

      Important to grind the flax seed. Cooking should not destroy benefit of flax seed… based on current studies… keep tuned in you never know when a study will come out challenging our beliefs.

  • Bryan

    Has anyone noticed the similarity of the chart showing the volume of industrial production of transfats since they were invented and the chart of heart attack deaths over the same period?

  • liohina

    You talk about avocados containing healthy monounsaturated fat, but you never mention that their ratio of omega 6 to omega 3 fatty acids is 15 or 16 to 1…definitely not good. All that and persin too??? (Sob!).

    –Inveterate avocado lover

  • jshm

    Dear Dr. Greger,

    Historically margarine has had high levels of trans fatty acids but modern spreads tend to have little or no trans fatty acids (listed as 0 g). Although, based on the FDA nutrition labelling this actually refers to less than 0.5 g of trans fat per serving. In addition, the saturated fat levels are much lower than butter. You mention that no amount of trans fat is advised, but is less than 0.5 g per serving negligible? And based on the low levels of trans fat and saturated fat, are vegan spreads an acceptable part of a standard diet?

    Best wishes,


  • Marshall Schools

    Soooooo how do you consider the fats to be different in grass fed meat and dairy? Or processed plant foods? So saturated fats in coconut oil? Coconut oil, at least organic unfiltered versions, are really healing. I’ve experienced it and so have many of my friends. How do we distinguish between the good and bad versions of each type of fat depending on how that food is treated?

  • vkat79

    Dear Dr. Greger, dear nutritionfacts community,

    Even after
    having watched a number of videos (also by Dr. Esselsytn), I still
    don’t seem to comprehend what the problem with oils is. I mean, not all
    of them are hydrogenated, right?
    I assume (or hope) there is a difference between consuming them with your meals and treating your hair or skin with oils?
    is it a bad thing to put hazelnut / avocado / olive / castor / … oil
    on my skin for an over-night treatment? Or putting some oil on my hair
    tips? Or putting it on my elbows when the skin is dry?
    And what about oil pulling?
    sure not all oils were created equally bad? Are grape seed oil and
    poppy seed oil as bad as safflower oil, even though it’s also high in
    PUFAs? I mean, I do get the whole foods approach, I’m a big fan myself!,
    butI love oil-lemon dressings for my salad, and I love using walnut
    oil, for example. I don’t use much oil, though.
    (Example: carrots, walnut oil, fresh lemon juice, chopped hazelnuts, pepper)

    I’d really love some answers … I’m confused and don’t know what to do :/

    THANKS in advance!


    • Thea

      VKat: I recently re-watched a video from Jeff Novick called “From Oil to Nuts”. This video did an EXCELLENT job of really explaining why you might want to stay away from all oils. I highly recommend the video.

      Some of the highlights include:
      * most oils are going to have too much omega 6s to omega 3s
      * oils are empty calories – worse than sugar when you do a comparison
      * oils are the high calorie-dense, a big problem for people who need to lose weight
      * oils which tend to have a better omega 3 ratio (say flaxseed) go rancid very, very quickly. (In fact, Dr. Greger has at least one video on common oils and how quickly they go rancid. You might want to find that one if you can. It’s really eye-opening.)
      * oils/high fat make your blood sluggish (I think that point was in the Jeff video)

      Having said all that, here is how I have personally synthesized the information I have seen on oils: It is best to avoid them if I can because of all of the reasons stated above, plus more. However, just like it is best to avoid sugar, that doesn’t mean that I will never eat sugar. I just try to limit it as best I can. That’s my personal decision.

      So, in the context of a truly healthy whole plant food based diet, I don’t think it would be all that bad if you have some (non-rancid!, good luck with that) walnut oil. (The key would be to keep it as minimum as possible. Or maybe some days make your dressing without the oil and other days have it in?)

      That’s my 2 cents anyway. Hope it helps.

      • vkat79

        Thea, thank you *soooo* much! :) I’ll watch the recommended video! Thanks for summarizing the main points :) Very kind of you!!

        I love this community & the spirit!