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6 Surprising Black Garlic Health Benefits + Side Effects

Written by Puya Yazdi, MD | Last updated:
Jonathan Ritter
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology) | Written by Puya Yazdi, MD | Last updated:

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We use garlic to season foods from entrees to french fries. For those who love garlic but always wished it just wasn’t so pungent, black garlic may be the ideal solution. Black garlic doesn’t have the same pungent odor as fresh garlic, and it could have a variety of health benefits.

What is Black Garlic?

Black garlic, a type of fermented or aged garlic, has numerous health benefits that range from its strong antioxidant nature to its potential role in cancer treatment [1].

With its unique sweet flavor and jelly-like consistency, it is widely known in Asia for its antioxidant properties [2].

Black garlic (Allium sativum L.) is a fermented product of garlic made by treating fresh garlic for an average of 10 days at high temperatures (40 to 60 °C) and high humidity. It undergoes a Maillard reaction, which causes different compounds to form during the reaction. The reaction also darkens white garlic into a black color [3].

Processes vary widely across suppliers, with aging treatment ranging from 4 to 40 days. One study found that 21 days of treatment at 70 degrees and 90% relative humidity was best for black garlic’s antioxidant abilities [1].

While you can add black garlic to your diet, black garlic supplements are also available.

Components

When garlic undergoes treatment to turn into black garlic, allicin, the component that gives fresh garlic its notorious odor, is converted into a variety of other compounds [4].

Black garlic has various antioxidants [4]:

  • Amadori/Heyns compounds: These are formed during the Maillard reaction. Amadori/Heyns compounds are strong antioxidants, and compared to fresh garlic, black garlic has up to 40 to 100 times more of these compounds [2].
  • 5-hydroxymethylfurfural: This is an antioxidant that also has some anti-inflammatory effects. Compared to white garlic, black garlic has a higher amount of this beneficial component, as 5-HMF is created under very high heat [4].
  • Organosulfur compounds: Diallyl sulfide, diallyl disulfide, diallyl trisulfide, and diallyl tetrasulfide [4]
  • Pyruvate: This is a key antioxidant and anti-inflammatory molecule of black garlic. It reduces nitric oxide and prostaglandin E2, both of which prolong and intensify inflammation [4].
  • S-allylcysteine
  • Tetrahydro-β-carbolines
  • N-fructosyl glutamate
  • N-fructosyl arginine
  • Allixin
  • Selenium
  • N-alpha-(1-deoxy-d-fructose-1-yl)-l-arginine
  • Other alkaloids, polyphenols, and flavonoids

Black garlic also contains nitrogen oxide, which has strong antiviral and antitumor effects [3].

It also contains 2-linoleoyl-glycerol, an anti-inflammatory molecule. It lowers levels of prostaglandin E2 and cytokines, which are key promoters and signals of the inflammatory response. They prolong and increase cell death, swelling, and the uncomfortable symptoms of an allergy, infection, or other sicknesses [4].

Mechanism of Action

Garlic contains a high abundance of hydrogen-sulfur donating compounds, which are very important for antioxidant properties to be possible. Allicin, an unstable component of garlic, is converted into organosulfur compounds, which are more stable and also contain hydrogen-sulfur donating capabilities [5].

Hydrogen-sulfur donating compounds are vital to antioxidant effects, as they activate the Nfr-2 factor [5].

Nfr-2 factors bind to antioxidant response elements, which trigger the release of various enzymes [5]:

All of these enzymes are important because they become powerful antioxidants, transforming damaging oxygens and nitrogens into nonreactive states that can significantly harm cells in the human body [5].

Health Benefits of Black Garlic

Black garlic is a safe foodstuff which can be used in the same way as fresh garlic, but it has not been approved by the FDA for medical use and generally lacks solid clinical research. Talk to your doctor before using black garlic as a supplement.

1) Heart Health

Black garlic improved the cholesterol of patients with mildly high cholesterol levels in various studies [2, 1].

In a 12-week human study (placebo) involving 60 people, 30 people were given 6 g of black garlic 2 times daily before meals. It increased HDL (good) cholesterol levels compared with the placebo group at the end of the study. However, there were no changes in LDL (bad cholesterol) [2, 1].

Black garlic’s high levels of organosulfur compounds also relax blood vessels, which leads to lower blood pressure. In a 12-week study of 79 high blood pressure patients, they took either 2 or 4 black garlic tablets daily. Their average blood pressure decreased by 11.8 mm Hg [6, 7].

Eating black garlic as part of your diet may help maintain or improve cardiovascular health, but more human studies are required to understand the effects of black garlic supplements on the heart.

Other Potential Benefits

There is some evidence suggesting additional benefits for black garlic, but these are largely limited to cell and animal studies. Clinical trials will either confirm or refute these potential benefits in humans; talk to your doctor before using black garlic as a supplement.

2) Antioxidants

These results are limited to cell and animal studies so far. Clinical trials will be required to determine what effects black garlic’s antioxidants may have on human health.

Black garlic reduces allicin content by converting allicin, an unstable compound, into more stable compounds that turn out to be great antioxidants. The Maillard reaction causes brown discoloration of garlic and generates various compounds that have antioxidant properties [2].

Black garlic decreased UV skin damage liver damage in mice [1].

Also, black garlic juice fed to insulin-deficient mice reduced harmful reactive substances (thiobarbituric acid) that cause damage to the blood, liver, and kidneys [1].

Black garlic is 10 times more effective than fresh garlic in its antioxidant power. The garlic mimics an enzyme (superoxide dismutase) by defending cells from hydrogen peroxide, a reactive oxygen species that can cause tissue damage [2].

3) Inflammation

Larger and more robust clinical trials will be required to determine the role (if any) of black garlic in fighting inflammation in humans. All we can really say for now is that eating black garlic as part of a healthy diet won’t hurt.

Black garlic decreased blood clotting effects caused by platelet aggregation in both human and animal studies [1, 2].

In a human cell study, 5-HMF, an antioxidant found in black garlic, stopped the activation of nuclear factor kappa B (NF-κB) [1, 2].

This molecule controls the release of cytokines that prolong and stimulate TNF-α activated cells [1, 2].

TNF-α activated cells promote the inflammatory response and increase blood flow, swelling, and defensive cells to the area [1, 2].

Black garlic also lowered the quantity of proteins that join cells and create blood clots. It also lowered the number of cells that cause inflammation and cell damage [1, 2].

In a cell study using macrophages (immune cells), black garlic decreased the production of nitric oxide, TNF-α, and prostaglandin E2, which are all key promoters of inflammation. It accomplished this by decreasing various protein and enzyme levels, specifically of NO synthase, TNF-α, and cyclooxygenase-2 protein [1, 2].

In a mouse study, rodents were given 120 mg/kg of black garlic experienced decreased levels of cytokines TNF-α and IL-6 in the blood [1, 2].

4) Allergies

According to animal and cell studies, black garlic may decrease the markers of allergies and prevent allergic reactions, but no human studies have yet been conducted.

Allergies are related to immunoglobulin E (IgE) antibodies and mast cells that all contribute to promoting long-term inflammation. Specifically, a type I allergy response is activated by the IgE receptor that is on the outside surface of immune cells [2, 1].

A cell study testing a 2 mg/mL treatment of black garlic resulted in a decrease of the inflammatory enzymes (β-hexosaminidase and TNF-α). This prevented an allergic response [2, 1].

In another cell study, 50 μg/mL of black garlic inhibited key allergy-promoting molecules (prostaglandin E2, leukotriene B4, and cyclooxygenase-2), and prevented signaling (phosphorylation of Syk, phospholipase A2, and 5-lipoxygenase) that can lead to cell attack by immune system cells called macrophages [2, 1].

Mice treated with black garlic also had a decreased allergic response visible on their skin [2, 1].

5) Liver Damage

Black garlic may benefit liver health, but human studies have yet to be conducted.

Rats with induced oxidative liver damage were treated with black garlic. Black garlic treatment significantly lowered markers of liver injury (AST, ALT, ALP, and LDH levels) [2].

Black garlic also increased the normal activity and metabolism of the liver as the garlic increased levels of a molecule called CYP2E1. The black garlic also decreased fatty liver deposits and rebalanced liver cell diameters to optimal size [2].

6) Brain Cells & MSG

You’ve probably heard of the seasoning MSG (monosodium glutamate). In rat brain cells, MSG damaged the Purkinje cells in the brain (cerebellum and hippocampus), but its effect on humans is unclear [2, 1].

The cerebellum and the hippocampus are vital parts of the brain, as they control muscle coordination and make memory retention possible. In rats, black garlic extract helped decrease Purkinje cell damage caused by MSG [2, 1].

Because MSG is controversial (with many studies finding no harmful effects whatsoever), the relevance of this black garlic study on rats is unclear. Human trials will be required.

Cancer Research

Scientists are investigating whether any of the active compounds of black garlic have an effect on cancer cells. This is very early research on cells only, and no particular conclusion can be drawn from it about the effect of black garlic on cancer in a living animal or human. Many compounds have “anti-cancer” effects in cells which do not pan out in a living system.

In some cancer cells, direct exposure to black garlic decreases JNK and p38MAPK signaling molecules, which are heavily involved in the onset of cancer. Some of these cancer cells are the A549 lung cancer cell, HepG2 liver cancer cell, and MCF-7 breast cancer cell [4].

Black garlic and its active compounds are currently being investigated in:

  • Leukemia [2]
  • Stomach cancer [8]
  • Colon cancer [2]
  • Endometrial cancer [2]

Supplementing with Black Garlic

Forms of Supplementation

Black garlic is taken in tablet form as supplements, or in bulb form in Asian supermarkets.

Side Effects

There are no known major side effects of black garlic, which is considered safe to use as food.

A rare case has been reported, in which black garlic has led to a case of pneumonia. It could not be determined if it was an immune reaction or a case of toxicity [9].

Limitations and Caveats

Few extensive human clinical trials have been conducted, so it is difficult to predict the long-term effects of black garlic. Many more clinical trials will be required.

Differences Between Fresh Garlic and Black Garlic

Black garlic has increased fructose and glucose content (as a result of the Maillard reaction it undergoes under heat), explaining its sweet flavor [10].

In a study of immune cells from 21 volunteers, black garlic showed stronger antioxidant activity than fresh garlic [11].

Fresh garlic, however, had stronger anti-inflammatory properties because of its lower sugar content [12].

About the Author

Puya Yazdi

Puya Yazdi

MD
Dr. Puya Yazdi is a physician-scientist with 14+ years of experience in clinical medicine, life sciences, biotechnology, and nutraceuticals.
As a physician-scientist with expertise in genomics, biotechnology, and nutraceuticals, he has made it his mission to bring precision medicine to the bedside and help transform healthcare in the 21st century.He received his undergraduate education at the University of California at Irvine, a Medical Doctorate from the University of Southern California, and was a Resident Physician at Stanford University. He then proceeded to serve as a Clinical Fellow of The California Institute of Regenerative Medicine at The University of California at Irvine, where he conducted research of stem cells, epigenetics, and genomics. He was also a Medical Director for Cyvex Nutrition before serving as president of Systomic Health, a biotechnology consulting agency, where he served as an expert on genomics and other high-throughput technologies. His previous clients include Allergan, Caladrius Biosciences, and Omega Protein. He has a history of peer-reviewed publications, intellectual property discoveries (patents, etc.), clinical trial design, and a thorough knowledge of the regulatory landscape in biotechnology.He is leading our entire scientific and medical team in order to ensure accuracy and scientific validity of our content and products.

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