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Eating garlic may be good for your brain, particularly as you age. The pungent herb may protect brain health by fighting age-related changes in gut health linked to cognitive function, according to University of Louisville researchers.
The study, which was presented at the American Physiological Society's 2019 annual meeting, adds more credence to garlic's status as a superfood, and support for its powerful medicinal properties, which have been valued since ancient times.
A high diversity of gut bacteria tends to be associated with better health, but as you age, gut diversity may decline. At the same time, neurodegenerative diseases including Alzheimer's and Parkinson's tend to develop in later life, leading researchers to look into the association between changes in gut microbiota and cognitive decline associated with aging, and how garlic may help.
Garlic Compound Improves Gut Bacteria, Memory
The study involved 24-month-old mice, which is equivalent to between 56 and 69 years in humans. Some of the mice received allyl sulfide, a compound in garlic, which led to improved long- and short-term memory, as well as healthier gut bacteria,1 compared to mice that didn't receive the supplement.
Mice taking the garlic compound also had higher gene expression of neuronal-derived natriuretic factor (NDNF), a gene required for memory consolidation. Reduced gene expression of NDNF may be linked to cognitive decline.
"Our findings suggest that dietary administration of garlic containing allyl sulfide could help maintain healthy gut microorganisms and improve cognitive health in the elderly," study author Jyotirmaya Behera, Ph.D., said in a press release.2
The link between gut bacteria and neurological health is not new. People with dementia, for instance, have a different makeup of gut microbiota compared to those without.3 Researchers further explained in the journal Protein & Cell:4
"New researches indicate that gastrointestinal tract microbiota are directly linked to dementia pathogenesis through triggering metabolic diseases and low-grade inflammation progress.
A novel strategy is proposed for the management of these disorders and as an adjuvant for psychiatric treatment of dementia and other related diseases through modulation of the microbiota (e.g. with the use of probiotics)."
That garlic could act as a key modulator of gut microbiota is a more novel concept, although perhaps it shouldn't be, as garlic is a source of inulin, a type of water-soluble prebiotic fiber. Inulin assists with digestion and absorption of your food and plays a significant role in your immune function.
Inulin is a fructan, which means it is made up of chains of fructose molecules. In your gut, inulin is converted into short-chain fatty acids (SCFAs) that are then converted to healthy ketones that feed your tissues.
Aged Garlic Extract May Benefit Your Brain
Previous research has also highlighted the benefits of a specific type of garlic — aged garlic extract (AGE) — for brain health. Known to have strong anti-inflammatory effects, AGE improved short-term recognition memory and relieved neuroinflammation in rats with an Alzheimer's-like disease.5
The study used fresh garlic that was aged in order to create aged garlic extract, which produces beneficial organosulfur compounds including s-allyl cysteine (SAC), which is found in far greater quantities in aged garlic and black fermented garlic than it is in raw garlic.
AGE also contains thiosulfinates that have antioxidant effects, and more than 350 studies have demonstrated its safety and effectiveness in humans. AGE may protect the brain in a number of ways, including:6
- Protect against neurodegenerative conditions
- Prevent brain injury following ischemia
- Protect neuronal cells against apoptosis
- Preventing β-amyloid-induced oxidative death
"Moreover," researchers explained in the journal Nutrients, "treatment with AGE or S-allyl cysteine has been shown to prevent the degeneration of the brain's frontal lobe, improve learning and memory retention, and extend life span."7
Aged garlic extract has also been found to improve gut microbiota, including increased microbial richness and diversity after three months of use.8 AGE and SAC have even been highlighted as potential preventative and therapeutic agents for Alzheimer's disease.9 That being said, fresh garlic has also shown promise for memory function, including one study in which rats fed garlic had increased memory retention.10
Garlic Has Been Prized Since Ancient Times
The value of garlic has been recognized for centuries. There are references to garlic on Sumerian clay tablets dating back to 2600 B.C. In ancient Egypt, garlic was given to the working class to support heavy labor. And in the first Olympic games in Greece, the athletes ate garlic to increase stamina.11
In ancient Chinese medicine, garlic was used for digestion and to treat diarrhea and worm infestations, while in India, garlic was used for general healing as well as to treat fatigue, parasites, digestive issues, heart disease and arthritis.12
"It is fascinating to observe how cultures that never came into contact with one another came to the same conclusions about the role of garlic in health and disease. If folk wisdom is not ignored, it may teach us valuable lessons," researchers wrote in Nutrition Journal, and many of these lessons are being backed by science today. They continued:13
"With the onset of Renaissance, increasing attention was paid in Europe to the medical use of garlic. A leading physician of the 16th century, Pietro Mattiali of Siena, prescribed garlic for digestive disorders, infestation with worms and renal disorders, as well as to help mother during difficult childbirth.
In England, garlic was used for toothache, constipation, dropsy and plague. In modern era scientists have been trying to validate many of these properties of garlic, specially in terms of the identity of the active components, their mechanisms of action and exploring the potential benefits as food supplements."
Garlic Is Good for Your Heart
Garlic is known to prevent and treat a wide variety of cardiovascular and metabolic diseases, including atherosclerosis, thrombosis, high blood pressure and diabetes.14 Not only does it stimulate immune function, enhance detoxification and exert an antimicrobial effect, but it has strong antioxidant powers that support health.
In addition, taking garlic powder had a protective effect on the elastic properties of the aorta in elderly adults. The aorta is the largest of your body's arteries with the job of transporting blood from your heart to the rest of your body. Not only is aortic stiffness often seen with aging but it's associated with an increased risk of heart disease, heart attack, heart failure and stroke.15
However, among elderly adults who took garlic powder, the age-related increases in aortic stiffness were attenuated, with researchers concluding, "These data strongly support the hypothesis that garlic intake had a protective effect on the elastic properties of the aorta related to aging in humans."16
In separate research, consuming 2 grams of fresh garlic increased plasma concentrations of nitric oxide (NO) in healthy adults,17 which is beneficial for your heart and more. Nitric oxide is a soluble gas continually produced from the amino acid L-arginine inside your cells.
While nitric oxide is a free radical, it's also an important biological signaling molecule that supports normal endothelial function and protects your mitochondria — the little "power stations" in your cells that produce a majority of your body's energy in the form of ATP.
It's a potent vasodilator, helping relax and widen the diameter of your blood vessels, and healthy blood flow allows for efficient oxygenation of tissues and organs, and aids in the removal of waste and carbon dioxide. Further, NO improves brain neuroplasticity by improving oxygenation of the somatomotor cortex, a brain area that is often affected in the early stages of dementia.18
Garlic Fights Infections, Cancer
Garlic has immune stimulating properties and as such may be useful for fighting off a variety of infections. When 146 adults received either a placebo or garlic supplement for 12 weeks, those taking the garlic had significantly fewer colds and if they were infected they recovered faster.19
In another study involving AGE (aged garlic extract), those taking the garlic had reduced cold and flu severity, reduced symptoms and fewer days of suboptimal functioning or missed work or school. "Garlic contains numerous compounds that have the potential to influence immunity," according to researchers in the Journal of Nutrition.20
"These results suggest that AGE supplementation may enhance immune cell function and may be partly responsible for the reduced severity of colds and flu reported. The results also suggest that the immune system functions well with AGE supplementation, perhaps with less accompanying inflammation."21
Toward this end, the cancer-fighting effects of garlic are also well established. Garlic has been shown to kill cancer cells in laboratory studies, as well as shown promise when consumed via your diet.
Those who consume high amounts of raw garlic also appear to have a lower risk of stomach and colorectal cancers.22 Furthermore, among people with inoperable forms of colorectal, liver or pancreatic cancer, taking an extract of aged garlic for six months helped to improve immune function, which suggests it may be useful for helping your immune system during times of stress or illness.23
The Many Types of Healthy Garlic
You can't go wrong when eating garlic, but if you're not fond of the pungent flavor or are looking to boost the health effects even more, consider black garlic, which is produced by "fermenting" whole bulbs of fresh garlic in a humidity-controlled environment in temperatures of about 140 to 170 degrees F for 30 days.
Once out of the heat, the bulbs are then left to oxidize in a clean room for 45 days. This lengthy process causes the garlic cloves to turn black and develop a soft, chewy texture with flavors reminiscent of "balsamic vinegar" and "soy sauce," with a sweet "prune-like" taste.24 Even garlic haters may love the taste of black garlic, and this superfood has been found to have more antioxidant activity compared to fresh.25
Writing in Molecules, researchers noted, "[S]ome people are reluctant to ingest raw garlic due to its unpleasant odor and taste. Therefore, many types of garlic preparations have been developed to reduce these attributes without losing biological functions. Aged black garlic (ABG) is a garlic preparation with a sweet and sour taste and no strong odor."26
If you choose to eat fresh garlic, be aware that the fresh clove must be crushed or chopped in order to stimulate the release of an enzyme called alliinase, which in turn catalyzes the formation of allicin, which rapidly breaks down to form a number of different beneficial organosulfur compounds. So to "activate" garlic's medicinal properties, compress a fresh clove with a spoon or chop it finely before to swallowing it.
If you're worried about garlic breath, it's a small price to pay for the many health benefits you'll receive, but you can cut back on any resulting unpleasant odor by chewing raw apple, mint leaves or lettuce. All of these natural foods have been found to significantly reduce garlic breath,27 so you can eat garlic to your heart's content without worrying about offending others.