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How garlic and onions promote cardiovascular health

March 11, 2022 by Joel Fuhrman, MD


Summary


There have been many intervention studies adding garlic or onion to the diet and evaluating cardiovascular and metabolic indicators.1 Studies have used a variety of forms of onions and garlic, including garlic powder, garlic extract, onion peel extract, or the raw vegetables themselves. The evidence suggests that phytochemicals from these flavorful vegetables support cardiovascular health in several different ways: 

  • Helping to reduce blood pressure
  • Helping to reduce cholesterol
  • Helping to reduce blood glucose
  • Slowing blood clotting

 

Here’s some news that might bring tears (of joy) to your eyes: Onions, garlic and other Allium vegetables aren’t just delicious, nutritious and – let’s face it – highly odiferous. They are also the source of phytochemicals that have powerful benefits for your heart health.

Garlic and onion phytochemicals

Within about one minute after garlic is chopped or crushed, the enzyme alliinase produces an organosulfur compound called allicin; then allicin is converted to a number of other organosulfur compounds with beneficial antioxidant, anti-inflammatory, and anti-cancer effects.2 Other organosulfur compounds are thought to be absorbed intact, and then converted by the body to bioactive compounds.3, 4 Onions (and other Allium vegetables – chives, shallots, leeks, scallions, etc.) also contain some of these organosulfur compounds. The evidence suggests waiting 10 minutes to cook after chopping for the full effect of alliinase.5

Cooking tip: Looking for an easy way to crush garlic? Try using a hand-held grater. 

Onions are particularly rich in the flavonoid phytochemical quercetin, which is the most abundant flavonoid in onions. Red onions also contain anthocyanins. The outer layers of the onion contain more flavonoids, as does the portion nearer the root end. Flavonoids are known for their effects on cell signaling leading to anti-inflammatory and antioxidant effects.6,7

Cooking tip: To get the most “bang” for your caloric “buck” when eating red onions, be sure not to peel off too much of the outer layers, and cut it as close to the root end as possible. That’s because the outer layers of the onion contain more flavonoids, as does the portion nearer the root. 

Source
Allium vegetable consumption and health: An umbrella review of meta-analyses of multiple health outcomes
Garlic and onions: their cancer prevention properties
Garlic (Allium sativum L.): A Brief Review of Its Antigenotoxic Effects
Biological Properties and Bioactive Components of Allium cepa L.: Focus on Potential Benefits in the Treatment of Obesity and Related Comorbidities
Onions: A Source of Flavonoids

Garlic and onions may help lower cholesterol levels

The organosulfur compound allicin and another garlic phytochemical called ajoene are known to inhibit the enzyme responsible for cholesterol synthesis in vitro, suggesting that garlic could influence cholesterol levels.8  Multiple meta-analyses of randomized controlled trials on the effect of garlic supplements on lipid levels have been published. Overall, total and LDL cholesterol were reduced in both healthy participants and patients with elevated cholesterol.1

Only a few trials have been conducted on onions or onion extract. In women with normal cholesterol levels, two weeks of supplementation with onion peel extract decreased total and LDL-cholesterol compared to placebo.9 Similarly, raw red onion twice a day for 8 weeks reduced cholesterol in overweight or obese women with polycystic ovary syndrome.10  

Video: How to Lower Blood Pressure and Cholesterol (free for members)

Sources
Ajoene, a garlic compound, inhibits protein prenylation and arterial smooth muscle cell proliferation
Effect of onion peel extract supplementation on the lipid profile and antioxidative status of healthy young women: a randomized, placebo-controlled, double-blind, crossover trial
Effects of raw red onion consumption on metabolic features in overweight or obese women with polycystic ovary syndrome: a randomized controlled clinical trial

Blood pressure benefits

Garlic phytochemicals could affect blood pressure in two ways: 

  • Through antioxidant effects leading to better vascular function
  • By inhibiting angiotensin-converting enzyme (ACE), the target of a common class of blood pressure medications.11 

Meta-analyses have found that supplemental garlic reduced systolic and diastolic blood pressure in participants with hypertension.1

Quercetin and other flavonoids are thought to reduce blood pressure in multiple ways: 

  • Increasing the production of nitric oxide in artery walls
  • Via their anti-inflammatory effects
  • Increasing antioxidant enzymes.12 
  • In particular, quercetin may also affect ion transport and fluid balance.13

Related: Eating Berries Reduces Your Risk of Heart Attack

In a few studies, supplemental onion improved vascular function or blood pressure. Onion peel extract supplementation – twice a day for 12 weeks – in overweight and obese participants improved vascular function, compared to placebo.14 In another study of onion skin extract, in overweight or obese participants with pre-hypertension or stage 1 hypertension, systolic blood pressure was reduced, compared to placebo.15 

Sources
Effect of garlic on blood pressure: a meta-analysis
Habitual intake of flavonoid subclasses and incident hypertension in adults
Actions of Quercetin, a Polyphenol, on Blood Pressure
Effect of onion peel extract on endothelial function and endothelial progenitor cells in overweight and obese individuals
Effects of a quercetin-rich onion skin extract on 24 h ambulatory blood pressure and endothelial function in overweight-to-obese patients with (pre-)hypertension: a randomised double-blinded placebo-controlled cross-over trial

Effects on fasting blood glucose

In 40 patients with metabolic syndrome, raw crushed garlic twice a day for 4 weeks reduced systolic and diastolic blood pressure, triglycerides, and fasting blood glucose.16 In women with breast cancer, eating fresh yellow onion daily for 8 weeks decreased fasting blood glucose compared to a placebo group during doxorubicin chemotherapy, a treatment which may reduce sensitivity to insulin. The onion group also showed improvement in a measure of insulin sensitivity.17

In a meta-analysis of studies on patients with diabetes, garlic supplementation reduced fasting blood glucose and HbA1c, and the effect on HbA1c was greater with a longer duration of supplementation.18 

Sources
Effect of Raw Crushed Garlic (Allium sativum L.) on Components of Metabolic Syndrome
Consumption of Fresh Yellow Onion Ameliorates Hyperglycemia and Insulin Resistance in Breast Cancer Patients During Doxorubicin-Based Chemotherapy: A Randomized Controlled Clinical Trial
The effect of garlic on lipid profile and glucose parameters in diabetic patients: A systematic review and meta-analysis

Antiplatelet effects

Organosulfur compounds from garlic and onions inhibit platelet aggregation in vitro. Trials on garlic supplementation overall have found a modest but significant antiplatelet effect,19 which could help prevent heart attacks by slowing blood clotting. 

A comparison of different Allium vegetables that tested antiplatelet activity on blood from healthy volunteers found that garlic and shallot had the strongest antiplatelet effects, and chives and onion had milder effects.20 

Sources
Garlic shows promise for improving some cardiovascular risk factors
Relationships Between Bioactive Compound Content and the Antiplatelet and Antioxidant Activities of Six Allium Vegetable Species
 

Read: The End of Heart Disease

 
References
  1. Wan Q, Li N, Du L, et al. Allium vegetable consumption and health: An umbrella review of meta-analyses of multiple health outcomes. Food Sci Nutr 2019, 7:2451-2470.
  2. Nicastro HL, Ross SA, Milner JA. Garlic and onions: their cancer prevention properties. Cancer Prev Res (Phila) 2015, 8:181-189.
  3. Morales-Gonzalez JA, Madrigal-Bujaidar E, Sanchez-Gutierrez M, et al. Garlic (Allium sativum L.): A Brief Review of Its Antigenotoxic Effects. Foods 2019, 8.
  4. Higdon J, Drake VJ: Organosulfur Compounds from Garlic. In An Evidence-Based Approach to Phytochemicals and Other Dietary Factors. 2nd edition2013: 149-157
  5. Song K, Milner JA. The influence of heating on the anticancer properties of garlic. J Nutr 2001, 131:1054S-1057S.
  6. Marrelli M, Amodeo V, Statti G, Conforti F. Biological Properties and Bioactive Components of Allium cepa L.: Focus on Potential Benefits in the Treatment of Obesity and Related Comorbidities. Molecules 2018, 24.
  7. Rodrigues AS, Almeida DPF, Simal-Gandara J, Perez-Gregorio MR: Onions: A Source of Flavonoids. In Flavonoids - From Biosynthesis to Human Health. Intech Open; 2017
  8. Ferri N, Yokoyama K, Sadilek M, et al. Ajoene, a garlic compound, inhibits protein prenylation and arterial smooth muscle cell proliferation. Br J Pharmacol 2003, 138:811-818.
  9. Kim J, Cha YJ, Lee KH, Park E. Effect of onion peel extract supplementation on the lipid profile and antioxidative status of healthy young women: a randomized, placebo-controlled, double-blind, crossover trial. Nutr Res Pract 2013, 7:373-379.
  10. Ebrahimi-Mamaghani M, Saghafi-Asl M, Pirouzpanah S, Asghari-Jafarabadi M. Effects of raw red onion consumption on metabolic features in overweight or obese women with polycystic ovary syndrome: a randomized controlled clinical trial. J Obstet Gynaecol Res 2014, 40:1067-1076.
  11. Wang HP, Yang J, Qin LQ, Yang XJ. Effect of garlic on blood pressure: a meta-analysis. J Clin Hypertens (Greenwich) 2015, 17:223-231.
  12. Cassidy A, O'Reilly EJ, Kay C, et al. Habitual intake of flavonoid subclasses and incident hypertension in adults. Am J Clin Nutr 2011, 93:338-347.
  13. Marunaka Y, Marunaka R, Sun H, et al. Actions of Quercetin, a Polyphenol, on Blood Pressure. Molecules 2017, 22.
  14. Choi EY, Lee H, Woo JS, et al. Effect of onion peel extract on endothelial function and endothelial progenitor cells in overweight and obese individuals. Nutrition 2015, 31:1131-1135.
  15. Brull V, Burak C, Stoffel-Wagner B, et al. Effects of a quercetin-rich onion skin extract on 24 h ambulatory blood pressure and endothelial function in overweight-to-obese patients with (pre-)hypertension: a randomised double-blinded placebo-controlled cross-over trial. Br J Nutr 2015, 114:1263-1277.
  16. Choudhary PR, Jani RD, Sharma MS. Effect of Raw Crushed Garlic (Allium sativum L.) on Components of Metabolic Syndrome. J Diet Suppl 2018, 15:499-506.
  17. Jafarpour-Sadegh F, Montazeri V, Adili A, et al. Consumption of Fresh Yellow Onion Ameliorates Hyperglycemia and Insulin Resistance in Breast Cancer Patients During Doxorubicin-Based Chemotherapy: A Randomized Controlled Clinical Trial. Integr Cancer Ther 2017, 16:276-289.
  18. Shabani E, Sayemiri K, Mohammadpour M. The effect of garlic on lipid profile and glucose parameters in diabetic patients: A systematic review and meta-analysis. Prim Care Diabetes 2019, 13:28-42.
  19. Ackermann RT, Mulrow CD, Ramirez G, et al. Garlic shows promise for improving some cardiovascular risk factors. Arch Intern Med 2001, 161:813-824.
  20. Beretta HV, Bannoud F, Insani M, et al. Relationships Between Bioactive Compound Content andthe Antiplatelet and Antioxidant Activities of Six Allium Vegetable Species. Food Technol Biotechnol 2017, 55:266-275.

Joel Fuhrman, M.D. is a board-certified family physician, seven-time New York Times bestselling author and internationally recognized expert on nutrition and natural healing, who specializes in preventing and reversing disease through nutritional methods. Dr. Fuhrman coined the term “Nutritarian” to describe his longevity-promoting, nutrient dense, plant-rich eating style.
 
For over 30 years, Dr. Fuhrman has shown that it is possible to achieve sustainable weight loss and reverse heart disease, diabetes and many other illnesses using smart nutrition. In his medical practice, and through his books and PBS television specials, he continues to bring this life-saving message to hundreds of thousands of people around the world.

 

Comments (0):

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vaporz

03/14/2022 11:51 AM

For those who dislike onions, try the G-BOMBS bars (https://shop.drfuhrman.com/foods/nutrition-bars-and-popems/), you can't taste the onions.  Also, I find the finer I chop them, the less I can taste them,  I use a mini-chopper to keep from tearing up. I then add the raw onion to my soup/stew/chili and hardly notice them.

linlamm7

03/29/2022 11:26 PM

I have a hiatal hernia and sometimes eating onions and garlic can be problematic. What do you recommend for people who have GERD and/or heartburn related issues, yet want to get the health benefits from eating garlic and onions?

 

Lisa Fuhrman replies:

04/05/2022 01:23 PM

For questions reguarding your health, check out our Ask the Doctor forum: https://www.drfuhrman.com/communities/ask-the-doctor.aspx

h

dukhniwaran

04/05/2022 11:02 PM

I saute them first either in a small amount of oil or in water.

 

 

Lorri

04/06/2022 12:19 AM

Dr. Fuhrman's the best!

Lulit

04/06/2022 10:55 AM