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:

How to Maximize Nutrient Absorption

Unhealthy lifestyle behaviors associated with an increased risk of premature death include smoking, excessive alcohol drinking, and not eating enough greens. The best way to get your greens is in whichever way you’ll eat the most of them, and one way to sneak extra greens into your daily diet is with whole-food smoothies, “a potent blend of good nutrition” in a quick, portable, delicious form.  

The Mayo Clinic offers a basic green smoothie recipe, combining the healthiest of fruits and the healthiest of vegetables, berries and dark green leafies, respectively. It calls for 2 ounces of baby spinach, which is about a cup and a half. Consider adding in some curly parsley, another mild beginner green to start with. Surprisingly, the sweetness of the fruit masks any bitterness from the greens such that the pickiest of children love these smoothies, as do adults who otherwise would not consume dark green leafy vegetables—or even fruit—for breakfast. Indeed, the average teen may only get about 1/20th of a serving of fruit otherwise—and Froot Loops don’t count. 

Offering smoothies can have a dramatic effect on fruit consumption for “students who do not want to take time peeling or chewing fruits.” (Who doesn’t have time to chew a fruit?!) The milkshake-y texture of smoothies may not only boost the quantity of fruit and vegetable consumption, but also the quality. 

Carotenoid phytonutrients, like beta-carotene and lycopene, can exist as microscopic crystals trapped inside the cell walls of fruits and vegetables. They’re only released when the cells are disrupted, which is why we have to chew really well. We either have to chew better or choose plants that are easier to chew. For example, while tomatoes have more beta-carotene than watermelon does, watermelon’s beta-carotene is more bioaccessible because its cell walls are wimpy compared with the smaller and tougher cell walls of other fruits and vegetables. To maximize nutrient release, food particle size would ideally be reduced to smaller than the width of the individual plant cells, but you can’t do that with chewing. Most vegetable particles end up greater than two millimeters when you chew them, whereas if we broke open all the cells, we could release much more nutrition, as you can see in my video, Are Green Smoothies Good for You?. The particle size distribution from chewing is about what you’d get blending in a food processor for about five seconds or one of those high-speed blenders for maybe half a second. Just 40 seconds in a blender can break down spinach to a subcellular level. 

Why does that matter? Let’s look at folate, the B vitamin in greens that is especially important for women of child-bearing age. Feed people a cup of spinach a day for three weeks and their folate goes up compared to control. What happens if you eat finely chopped spinach instead of whole leaves? You end up with more than twice as much in your bloodstream and the same absorption-boosting effect with lutein, the green nutrient so important for our eyesight.

It’s not what you eat—it’s what you absorb.  

The boost for lutein was only 14%, so a few extra bites of the whole leafy greens would have given you just as much. Some other nutrients, such as vitamin C, aren’t affected by pre-chopping at all. This is also less of an issue with cooked vegetables. If you boil carrots for three minutes, regular chewing can release about ten times more beta-carotene bioaccessibility than eating them raw, but not as much as blended. Intense cooking, like boiling for 25 minutes, so damages the cell walls so even gulping down large particles can result in significant absorption. But, blending may double carotenoid availability, explaining why we may be able to absorb three times the alpha- and beta-carotene from pureed cooked carrots compared to mashed cooked carrots. So, blending vegetables—raw or cooked—into soups, sauces, or smoothies can maximize nutrient absorption. Whether you went to the store and bought it, or toiled in your garden to grow it, you might as well take full advantage of it.  


Check out my other videos that touch on smoothies:

For other tips on getting children of all ages to eat healthier, see Tricks to Get Kids to Eat Healthier at Home and Tricks to Get Adults to Eat Healthier.

Finally, learn more about the effect of cooking on nutrient loss and absorption from these videos: Best Cooking Method, Raw Food Nutrient Absorption, and Sometimes the Enzyme Myth Is True.

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:

What to Eat to Cure High Blood Pressure

High blood pressure ranks as the number-one risk factor for death and disability in the world. In my video, How to Prevent High Blood Pressure with Diet, I showed how a plant-based diet may prevent high blood pressure. But what do we do if we already have it? That’s the topic of How to Treat High Blood Pressure with Diet

The American Heart Association (AHA), the American College of Cardiology (ACC, and the Centers for Disease Control and Prevention (CDC) recommend lifestyle modification as the first-line treatment. If that doesn’t work, patients may be prescribed a thiazide diuretic (commonly known as a water pill) before getting even more meds until their blood pressure is forced down. Commonly, people will end up on three drugs, though researchers are experimenting with four at a time. Some patients even end up on five different meds.

What’s wrong with skipping the lifestyle modification step and jumping straight to the drugs? Because drugs don’t treat the underlying cause of high blood pressure yet can cause side effects. Less than half of patients stick with even the first-line drugs, perhaps due to such adverse effects as erectile dysfunction, fatigue, and muscle cramps.

What are the recommended lifestyle changes? The AHA, ACC, and CDC recommend controlling one’s weight, salt, and alcohol intake, engaging in regular exercise, and adopting a DASH eating plan.

The DASH diet has been described as a lactovegetarian diet, but it’s not. It emphasizes fruits, vegetables, and low-fat dairy, but only a reduction in meat consumption. Why not even more plant-based? We’ve known for decades that animal products are significantly associated with blood pressure. In fact, if we take vegetarians and give them meat (and pay them enough to eat it!), we can watch their blood pressures go right up.

I’ve talked about the benefits to getting blood pressure down as low as 110 over 70. But who can get that low? Populations centering their diets around whole plant foods. Rural Chinese have been recorded with blood pressures averaging around 110 over 70 their whole lives. They eat plant-based day-to-day, with meat only eaten on special occasions.

How do we know it’s the plant-based nature of their diets that was so protective, though?

Because in the Western world, as the American Heart Association has pointed out, the only folks getting down that low on average were those eating strictly plant-based diets, coming in at about 110 over 65.

So were the creators of the DASH diet just not aware of this landmark research done by Harvard’s Frank Sacks? No, they were aware. The Chair of the Design Committee that came up with the DASH diet was Dr. Sacks himself. In fact, the DASH diet was explicitly designed with the number-one goal of capturing the blood pressure-lowering benefits of a vegetarian diet, yet including enough animal products to make it “palatable” to the general public.

You can see what they were thinking. Just like drugs never work—unless you actually take them. Diets never work—unless you actually eat them. So what’s the point of telling people to eat strictly plant-based if few people will do it? So by soft-peddling the truth and coming up with some kind of compromise diet, the on a population scale maybe you’d do more. Ok, but tell that to the thousand U.S. families a day that lose a loved one to high blood pressure. Maybe it’s time to start telling the American public the truth.

Sacks himself found that the more dairy the lactovegetarians ate, the higher their blood pressures. But they had to make the diet acceptable. Research has since shown that it’s the added plant foods—not the changes in oil, sweets, or dairy—that appears to the critical component of the DASH diet. So why not eat a diet composed entirely of plant foods?

A recent meta-analysis showed vegetarian diets are good, but strictly plant-based diets may be better. In general, vegetarian diets provide protection against cardiovascular diseases, some cancers, and even death. But completely plant-based diets seem to offer additional protection against obesity, hypertension, type-2 diabetes, and heart disease mortality. Based on a study of more than 89,000 people, those eating meat-free diets appear to cut their risk of high blood pressure in half. But those eating meat-free, egg-free, and dairy-free may have 75% lower risk.

What if we’re already eating a whole food, plant-based diet, no processed foods, no table salt, yet still not hitting 110 over 70? Here are some foods recently found to offer additional protection: Just a few tablespoons of ground flaxseeds a day was 2 to 3 times more potent than instituting an aerobic endurance exercise program and induced one of the most powerful, antihypertensive effects ever achieved by a diet-related intervention. Watermelon also appears to be extraordinary, but you’d have to eat around 2 pounds a day. Sounds like my kind of medicine, but it’s hard to get year-round (at least in my neck of the woods). Red wine may help, but only if the alcohol has been taken out. Raw vegetables or cooked? The answer is both, though raw may work better. Beans, split peas, chickpeas, and lentils may also help a bit.

Kiwifruits don’t seem to work at all, even though the study was funded by a kiwifruit company. Maybe they should have taken direction from the California Raisin Marketing Board, which came out with a study showing raisins can reduce blood pressure, but only, apparently, compared to fudge cookies, Cheez-Its, and Chips Ahoy.


The DASH diet is one of the best studied, and it consistently ranks as US News & World Report’s #1 diet. It’s one of the few diets that medical students are taught about in medical school. I was so fascinated to learn of its origins as a compromise between practicality and efficacy.

I’ve talked about the patronizing attitude many doctors have that patients can’t handle the truth in:

What would hearing the truth from your physician sound like? See Fully Consensual Heart Disease Treatment and The Actual Benefit of Diet vs. Drugs.

For more on what plants can do for high blood pressure, see:

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: