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Raw vs. Cooked Garlic and Onions for Blood Thinning

As we age, our arteries stiffen. In my video Inhibiting Platelet Activation with Garlic and Onions, you can see charts showing measurements of the stiffness of our aorta, the main artery coming off the heart, as we get older and older. “As the aorta stiffens it leads to a range of linked pathphysiological changes,” such as exposing our brain and kidneys to greater pressure fluctuations, which may increase the risk of stroke and impairment of kidney function.

However, those who consume garlic—less than a quarter teaspoon of garlic powder a day—appear to have less stiffness in their aortas. We think this is because garlic seems to improve the function of the inner lining of our arteries, which helps our arteries relax. But the protective mechanisms of garlic against cardiovascular diseases are multiple, and include a combination of anti-clotting, clot-busting, antioxidant, and blood pressure- and cholesterol-lowering effects. The latest review suggests that long-term garlic intake may drop bad cholesterol levels about 10 percent, and the blood-thinning effects are such that the American Society of Anesthesiology recommends garlic intake be stopped a week before elective surgery.

Or, presumably, you could just cook it to death. Unlike the anticlotting components concentrated in the yellow fluid around tomato seeds, which are heat stable, the antiplatelet activity in garlic and onions is lost with cooking. When comparing  platelet inhibition, garlic appears about 13 times more potent than onion, and eating garlic raw appears to be better than cooked. This suggests that “garlic and onion could be more potent inhibitors of blood [clotting] if consumed in raw than in cooked or boiled form.” So, it might be good to cook garlic right before surgery, but what about the rest of the time when we’re trying to suppress platelet over-activity to decrease the risk of heart attacks and stroke? “As garlic and onion are normally consumed in cooked food, their efficacy as preventive herbs in cardiovascular disease may be doubtful.” But, we can put some raw onion on salads and raw garlic in salsa, dressings, dips, or pesto, right?

Or, we can crush or chop it, wait ten minutes, and then cook it. Researchers demonstrated the platelet-inhibiting power of raw garlic. If you cook it for just a few minutes, it does fine; but after cooking for about five minutes, the benefit is abolished. If, however, you pre-crush the garlic and wait, some of the antiplatelet activity is retained a bit longer. That’s because the enzyme that makes the antiplatelet compounds is activated by crushing but destroyed by heat faster than it creates the compounds. So, by crushing first and letting the enzyme work its magic before cooking, one can delay the loss of function.

Even better, though, is that, (as I discussed in my video Second Strategy to Cooking Broccoli with mustard powder), the addition of a little raw garlic juice to cooked garlic can restore the “full complement of antiplatelet activity that was completely lost without the [raw] garlic addition.”

When onions are cooked, the antiplatelet activity is similarly abolished within ten minutes, but then something strange happens. After 20 or 30 minutes of cooking, the effect on platelets is reversed and appears to make matters worse. Significant pro-platelet activation effects are seen, “suggesting that extensively cooked onions may stimulate rather than inhibit” platelets. That was in a test tube, though. Thankfully, when tested in people, even when onions are dropped in boiling water, fried for 10 minutes, and then left to simmer for 30 minutes, platelet activation drops within one to three hours after eating onion soup.


For background on what platelets are, what they do, and why we should care, see Inhibiting Platelet Aggregation with Berries and Inhibiting Platelet Activation with Tomato Seeds.

What else can garlic do? Check out:

What was that about mustard powder boosting the benefits of broccoli? See my Second Strategy to Cooking Broccoli video. Broccoli is also a potent activator of our liver’s detoxifying enzymes. Learn more in my Best Food to Counter the Effects of Air Pollution video.

Wondering whether it’s better to cook vegetables or eat them raw? See Best Cooking Method and for a surprise update, The Best Way to Cook Sweet Potatoes.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Discuss

Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.


53 responses to “Raw vs. Cooked Garlic and Onions for Blood Thinning

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  1. It’s stated that 1/4 teaspoon of powdered garlic is effective.

    Isn’t garlic heated during the powdering process? I would think that the heating would make the garlic powder ineffective.

    1. RichardW, Dr Greger writes that the antiplatelet activity in garlic and onions is lost in the cooking process, (unlike tomatoes, is heat sensitive). The garlic powder is effective for maintaining flexibility in the aorta, and can improve the lining of our arteries. Different mechanisms.

    2. Garlic powder (like olive oil) is a ‘processed food’. I have never understood, why even go there? Fresh garlic is dirt cheap, as well is fresh onions.

  2. What about onions vs challots?
    Most articles say challots beat onions in several key nutritional areas.
    But I’ve never seen discussion about the effects cooking has on each.
    –Also, good to see there actually is value in garlic powder!

  3. Hi, Dommy. I am guessing that challots and shallots are the same thing? There is little research specifically on shallots, but they are allium family plant foods like onions and garlic, and as such should be similar. I would love to see the articles you mention, if you would not mind sharing. Most of the existing research comes from Iran, where shallots have been used in traditional medicine. You might be interested in this article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3874089/
    I hope that helps!

    1. Hi Christine,

      You’re right, it’s “shallots.”

      Here’s what is saved in my “Health” folder:

      “Overall, shallots have better nutrition profile than onions. On a weight per weight basis, they have more antioxidants, minerals, and vitamins than onions.”
      https://www.nutrition-and-you.com/shallots.html

      “Shallots have a higher phenolic content than many onions, making them particularly effective against liver cancer cells, according to Rui Hai Liu, a food scientist at Cornell University.”
      “[Shallots are] valued not only for their unique flavor and availability but also for their significant nutrient value, which is actually superior to common onions in a number of ways. Let’s take a closer look . . .”
      https://www.organicfacts.net/health-benefits/vegetable/shallots.html

      https://www.nutritionvalue.org/Shallots%2C_raw_nutritional_value.html
      https://www.nutritionvalue.org/Onions%2C_raw_nutritional_value.html
      https://academic-corner-news.blogspot.com/

      Rereading the above just now, “onions vs shallots” could be called a tossup, depending on one’s goals. Thanks for the ncbi link, will read it later.

    2. Christine, Could you clarify the following from the study on platelet aggregation in high v low quercetin soup?

      Did the participants actually eat the onions that were in the soup–or did they just eat the broth?

      Also, does the study specify how long the onions were cooked to make a high quercetin soup? What was the low quercetin soup made of?

      Thanks so much. I can only access the abstract.

    1. I eat toast almost every morning with raw onions, garlic powder, sliced avacodo, and sometimes ground flax or nutritional yeast. It’s soooooo good! I even had it for breakfast when camping out in the deep woods this summer.

  4. It would be helpful to have an action summary at the end of videos like this one. Great info, but I’m confused. Such as:

    Best
    Raw, fresh garlic and onions

    Good
    Garlic crushed, wait 10 minutes, cook just a few minutes
    Adding garlic juice to cooked garlic (How do you make “garlic juice?” Can you buy it?)
    Cooked onions, any amount of time

    I’m with RichardW wanting to know where garlic powder and maybe onion powder fit in all this.

    I like both garlic and onion, so this is a potentially easy way for me to get health benefits.

    Thanks!

    1. Laughing.

      We have a few people who don’t like the videos at all and a few people who experience the blogs as if they were videos.

      Yes, you can buy garlic juice. One of the brands is Howard’s Garlic Juice about $4.50.

      To make your own: “Peel one bulb of garlic (this will give you a quarter to a third of a cup of juice depending on the size of the bulb). Blend the cloves in a small food processor until creamy and strain twice, once through a mesh strainer, then strain that liquid through a coffee filter.”

        1. I think I followed the garlic logic all the way through, but I got confused at the end of the onion logic.

          Somewhere in here, I lose the sense that I understand it: “After 20 or 30 minutes of cooking, the effect on platelets is reversed and appears to make matters worse. Significant pro-platelet activation effects are seen, “suggesting that extensively cooked onions may stimulate rather than inhibit” platelets. That was in a test tube, though. Thankfully, when tested in people, even when onions are dropped in boiling water, fried for 10 minutes, and then left to simmer for 30 minutes, platelet activation drops within one to three hours after eating onion soup.”

          I think the whole “boiling water, fried for 10 minutes, and then left to simmer for 30 minutes” is about where my mind has to work harder.

  5. I’m allergic to onions, shallots, leeks, etc, but can eat garlic, which I love. I eat way more than suggested here, and wonder if the higher consumption, some raw, some lightly cooked, some heavily cooked (soup cooking for 20 minutes, say) leads to a better result. I also wonder whether in the soup situation, whether adding it at the very end (say, with the kale!) meets the requirement for less cooking.

  6. Concering “Even better, though, is that, (as I discussed in my video Second Strategy to Cooking Broccoli with mustard powder), the addition of a little raw garlic juice to cooked garlic can restore the “full complement of antiplatelet activity that was completely lost without the [raw] garlic addition.”, what if instead of raw garlic juice we eat raw onions.

      1. Philip, it’s been my experience that the garlic & onion breath subsides soon after you start consuming them on a regular basis.

      2. “If you love garlic-flavored foods, you will probably keep eating them despite the potentially socially unacceptable consequences. One potential benefit to eating garlic is that the smell may act as an insect repellent, keeping away not only social acquaintances, but also more pesky mosquitoes and other insects.”

        https://www.livestrong.com/article/521817-how-to-eat-raw-garlic-not-have-garlic-breath/

        One plus: Various insects find the stench pretty repugnant too. Do they know something?

        (I stick to a couple of shakes of garlic powder on something or other at evening meal.)

            1. YR,

              You are right about Type O.

              Though ij shows me that it won’t be every Type O person.

              “However, people with type O blood have lower levels of Von Willebrand factor, a blood clotting agent that may help prevent life-threatening bleeding.”

              It is a really big deal.

              “Having blood type O almost trebles the risk of dying from serious injury because it does not clot as well, scientists have found. Data from 901 emergency care patients in Japan showed a death rate of 28 percent for those with type O blood. The death rate of patients from other blood groups combined was 11 percent.”

          1. The Food Science show on Food Network did a segment having some super smellers guess which people ate which foods by smelling their skin and, yes, I believe they guessed who ate garlic. That was years ago, but I think the person could smell the garlic eater’s arm and tell that they were a garlic eater.

  7. Are there any caveats that should be included?
    For instance how would this affect persons on low dose aspirin daily or who might be 0n other blood thinners? Did I miss this in the blog?

    1. Lida,

      Yes, it is high enough of a blood thinner that you would want to be aware of the other blood thinners in your diet and meds.

      1. Deb,
        Thanks
        I do wish Dr. Greger would issue warnings when and if they are warranted. In addition to the blood thinners I mentioned what about people who have digestive issues which would rule out onions and garlic entirely.

        1. Lida, when I was eating the standard American diet, I couldn’t digest onions & garlic. I could only eat them if they were cooked to death. But once I started eating more whole plant foods, that all changed. I can digest raw onions & garlic with no problem. It’s probably because my intestinal flora changed when I changed my diet.

          1. I experienced the EXACT same outcome! I couldn’t go near raw or slightly cooked onions/garlic when eating S.A.D. I now consume them raw all the time and have no adverse effect. It’s wonderful.

          2. bNancy and Joe,

            I think I have had the same thing.

            After age 40, I couldn’t eat garlics or onions when I was on the SAD diet. Didn’t matter if they were raw or cooked. I couldn’t eat garlic bread or sauce with too much garlic without it tearing me up inside, but I haven’t had any problems in quite a while.

      2. Thank you for the information, I had no idea and am on blood thinners. All my cooking usually has onions and garlic included so guess I need to run this by my doctor, thank you.

    2. Hi I’m a RN health support volunteer. Thanks for you great question. This was not addressed in the blog, but from a pharmacology perspective, there are no recommendations to avoid or limit garlic and onions while on daily aspirin therapy or blood thinners. The one blood thinner there there are significant dietary recommendations for would be warfarin or Coumadin as vitamin K will interact with the medication. That may just been this hasn’t been studied yet so as always, if someone is having excessive bleeding, they should consult their physician.

      NurseKelly

  8. I love eating plant-based and keeping up with all the great newly discovered health benefits of plant-based eating. However, I find it onerous to try to remember how to maximize the benefits of certain foods. Does anyone know of a chart, resource, or semi-inclusive resource that explicitly states the best methods for cooking specific foods (such as onion and garlic)?

  9. I use ‘freeze dried’ garlic and ‘air dried’ garlic, shallots and onions. That is what is on the bottle. I have roasted garlic powder in a bottle too. Love them all but I can’t halp but think there is some heat in the preparation of these jarred products. I use small amounts of raw scallions, red onions and garlic. As far as juice– just buy a garlic press and it lets some juice out and pulverized it that it can be spread lightly on the toast with avocado thinly sliced too. This topic is confusing, not much to follow but it sure makes one think. Hey, I have to get away in a quiet spot to think which is good for those that dislike the odor. I think more is not necessarily better in all cases like this. Be well.

  10. Great stuff.
    Just came back from working outside doing a lot of dirt and rock moving to facilitate drainage, tropical storm moisture(Ruth) coming our way…..so a real late lunch as usual.
    And a bit to tired and hungry to spend time cooking so……..heated up a bit of rice and tofu curried things but not really all that healthy. So how to make it better…watched the video while eating and…..then put in a bunch of powdered garlic…tastes actually good.

    And storming now a picture perfect day despite late lunch.Thanks Dr G

  11. If you eat the garlic raw do you still have to crush/chop and wait 10 minutes or can you eat whole clove raw without crushing and waiting 10 minutes?

  12. Raw garlic by itself is a challenge to consume and can be somewhat of a torturous endeavor. As lots of raw fruits and vegetables, brown rice and black beans are my daily consumption pattern, when I make a salad-meal, I also make a dressing…consisting of:

    5-10 cloves of raw garlic, 1/2 a raw onion, a stub of turmeric root, chunk of fresh ginger, an apple, mango, or pineapple, whatever greens may be lying around (cabbage, rocket, mustard greens, kale, spinach, cilantro, etc.), a few shakes of soy sauce, apple cider vinegar, and maybe some tomato juice if I need to thin it out. I make a blender full, and bottle the rest for tomorrow.

    This guarantees the best ‘poops’ the next morning, as I live to ‘fill the bowl’ on a daily basis. This is my one meal a day, as I do not consume any breakfast or lunch, am never really hungry throughout the day. Intermittent fasting works well for me.

  13. Raw garlic by itself is a challenge to consume and can be somewhat of a torturous endeavor. As lots of raw fruits and vegetables, brown rice and black beans are my daily consumption pattern, when I make a salad-meal, I also make a dressing…consisting of:

    5-10 cloves of raw garlic, 1/2 a raw onion, a stub of turmeric root, chunk of fresh ginger, an apple, mango, or pineapple, whatever greens may be lying around (cabbage, rocket, mustard greens, kale, spinach, cilantro, etc.), a few shakes of soy sauce, apple cider vinegar, and maybe some tomato juice if I need to thin it out. I make a blender full, and bottle the rest for tomorrow.

    This guarantees the best ‘poops’ the next morning, as I live to ‘fill the bowl’ on a daily basis. This is my one meal a day, as I do not consume any breakfast or lunch, am never really hungry throughout the day. Intermittent fasting works well for me.

  14. What about fermented black garlic? I’ve heard that the fermentation process can increase the amount of antioxidant levels found in raw garlic. Does anyone know if back garlic works better than its Fernando

    1. Pat,

      Here is an article on Black Garlic.

      It says it has less allicin, so it has less flavor. Allicin is something they have been studying to use when there is antibiotic resistance, but they are testing black garlic for its own list of benefits.

      “When compared with fresh garlic, BG does not release a strong off-flavor due to the reduced content of allicin, which was converted into antioxidant compounds such as bioactive alkaloids and flavonoid compounds during the aging process [1]. The changes of physicochemical properties are the main reasons for enhanced bioactivity of BG compared with fresh garlic. Besides daily consumption, several studies have reported that BG extract demonstrates several functions, such as antioxidation, antiallergic, antidiabetes, anti-inflammation, and anticarcinogenic effects [3], [4], [5], [6], “

  15. Re: shallots v onions

    Both contain healthy sulfur compounds, but their predominant phytonutrients differ:

    Onions are rich in quercetin; shallots are rich in isoliquiritigenin. Like quercetin, isoliquiritigenin has anti-platelet activity. And both phytos are among the top phytos for activating your nrf2 anti-oxidant team and inhibiting NFkB.

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