The Science of Stink: What Causes Garlic Breath?

Benefits of Garlic

Story at-a-glance -

  • Many of garlic’s therapeutic effect comes from its sulfur-containing compounds, such as allicin, which are also what give it its characteristic smell
  • Garlic has immune-boosting properties and is beneficial for heart health, fighting cancer, warding off colds and flus, and reducing inflammation
  • As allicin in garlic digests in your body, it produces sulfenic acid, a compound that reacts with dangerous free radicals more effectively than any other known compound
  • Black (fermented) garlic and sprouted garlic may have even more health potential than fresh garlic
  • To get the therapeutic benefits of garlic, be sure to crush the clove before you eat it; this stimulates the release of an enzyme called alliinase, which in turn catalyzes the formation of allicin

By Dr. Mercola

Eating a clove or two of fresh garlic a day may indeed keep the doctor away, in part because it has immune-boosting, antibacterial, antiviral, and anti-fungal effects.

A member of the allium family of vegetables, along with other superfoods like onions, scallions, chives, and leeks, garlic is one of the oldest cultivated plants in the world. As reported by the George Mateljan Foundation, garlic was believed to have sacred qualities and was placed in the tomb of Pharaohs.

It was also given to slaves building the Egyptian pyramids as a tool for increasing strength and endurance, a use that was also valued by Greek and Roman civilizations, who served garlic to athletes and soldiers before sporting events or war, respectively.1

Even gravediggers in 18th-century France consumed garlic-infused wine as a way to ward off the plague, and soldiers during World War I and World War II used garlic to prevent gangrene.2 Today, we have a wealth of modern research to back up the centuries’ old claims, as garlic truly is deserving of its reputation for potent healing powers.

Garlic Fights Cancer, Heart Disease, and Drug-Resistant Bacteria

Garlic is rich in manganese, calcium, phosphorus, selenium, and vitamins B6 and C, so it’s beneficial for your bones as well as your thyroid. It’s thought that much of garlic’s therapeutic effect comes from its sulfur-containing compounds, such as allicin, which are also what give it its characteristic smell.

Other health-promoting compounds include oligosaccharides, arginine-rich proteins, selenium, and flavonoids.3 GreenMedInfo has assembled a list of studies demonstrating garlic's effects for more than 160 different diseases.4 In general, its benefits fall into four main categories:

  1. Reducing inflammation (reduces the risk of osteoarthritis and other disease associated with inflammation)
  2. Boosting immune function (antibacterial, antifungal, antiviral, and antiparasitic properties)
  3. Improving cardiovascular health and circulation (protects against clotting, retards plaque, improves lipids, and reduces blood pressure)
  4. Toxic to 14 kinds of cancer cells (including brain, lung, breast, gastric, and pancreatic)

In addition, garlic may be effective against drug-resistant bacteria, and research has revealed that as allicin digests in your body, it produces sulfenic acid, a compound that reacts with dangerous free radicals faster than any other known compound.5 This is one of the reasons why I named garlic as one of the top seven anti-aging foods you can consume.

Like many natural foods, it’s difficult to confine garlic to just one or two benefits, as it appears to offer benefits throughout your body. The University of Maryland Medical Center summed up some of its most promising uses:6

“…garlic is used to help prevent heart disease, including atherosclerosis or hardening of the arteries (plaque buildup in the arteries that can block the flow of blood and may lead to heart attack or stroke), high cholesterol, high blood pressure, and to boost the immune system. Eating garlic regularly may also help protect against cancer.

Garlic is rich in antioxidants. In your body, harmful particles called free radicals build up as you age, and may contribute to heart disease, cancer, and Alzheimer's disease. Antioxidants like those found in garlic fight off free radicals, and may reduce or even help prevent some of the damage caused over time.”

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Garlic May Help Ward Off Colds and Flu

With both immune-boosting and antiviral effects, it makes sense that garlic would be useful for fighting off infectious disease, and the scientific research backs this up. According to one study, those who consumed garlic daily for three months had fewer colds than those who took a placebo.

When they did come down with a cold, the duration of illness was shorter – an average of 4.5 days compared to 5.5 days for the placebo group.7 While this may not seem overly impressive, it's still better than the results achieved by the much-advertised flu drug Tamiflu.

If taken within 48 hours of onset of illness, Tamiflu might reduce the duration of flu symptoms by about a day to a day and a half. That's the extent of what this $100-plus treatment will get you. It's virtually identical to just taking garlic on a regular basis...

Garlic’s Role in Fighting Cancer

Garlic has been shown to kill cancer cells in laboratory studies, as well as show promise when consumed via your diet. One study showed that women who regularly ate garlic (along with fruits and vegetables) had a 35 percent lower risk of colon cancer. 8 Those who consume high amounts of raw garlic also appear to have a lower risk of stomach and colorectal cancers.9

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.10

Garlic Must Be Crushed to Get Its Therapeutic Properties

Fresh garlic is best if it’s health benefits you’re after, and 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.

Allicin, in turn, rapidly breaks down to form a number of different organosulfur compounds. So to “activate” garlic’s medicinal properties, compress a fresh clove with a spoon prior to swallowing it, or put it through your juicer to add to your vegetable juice.

A single medium-size clove or two is usually sufficient and is well-tolerated by most people. The active ingredient, allicin, is destroyed within one hour of smashing the garlic, so garlic pills are virtually worthless. You also won’t reap all the health benefits garlic has to offer if you use jarred, powdered, or dried versions.

Worse yet, at least two supermarket brands containing garlic powder imported from China have been found to be contaminated with high levels of lead, arsenic, and added sulfites.11 If you’re looking for a simple and delicious way to add more raw garlic to your diet, try this organic garlic salad dressing.

What Causes Garlic Breath?

Garlic is called “the stinking rose” for good reason… but unfortunately, many people shy away from too much garlic, fearing it will lead to bad breath. It’s the allicin in garlic, and the four compounds it breaks down into, that give garlic its stench. The worst offender is allyl methyl sulfide, which not only causes bad breath but can also add a unique lingering odor to your sweat and urine.12

The good news is that the smell of garlic goes away once you metabolize the smelly compounds. The bad news is that it can take up to two days for this to happen. I would encourage you to not avoid garlic based on its smell alone, however, as you’ll be missing out on one of the healthiest (not to mention tastiest) foods on the planet.

If you develop a socially offensive odor, try decreasing the amount of garlic you’re consuming until there is no odor present. Eating parsley can also help you to get rid of garlic breath, and citrus may help to mask it. If you drink milk, one study also found that it “may help reduce the malodorous odor in breath after garlic ingestion and mask the garlic flavor during eating.”13

Sprouting Garlic May Magnify Its Nutritional Potential

In an article published in the Journal of Agricultural and Food Chemistry, garlic sprouted for five days was found to have higher antioxidant activity than fresher, younger bulbs, and it had different metabolites, suggesting it also makes different substances.14 Researchers concluded that sprouting your garlic might be a useful way to improve its antioxidant potential. Extracts from this garlic even protected cells in a laboratory dish from certain types of damage.15

This isn’t really surprising when you consider the nutritional changes that typically occur in plants when they sprout. When seedlings grow into green plants, they make many new compounds, including those that protect the young plant against pathogens. The same thing is likely happening when green shoots grow from old heads of garlic.

Black Fermented Garlic Has Twice the Antioxidants of Fresh Garlic

Another little-known anecdote is that black garlic, which is basically fermented garlic, may be even healthier than other forms. In a 2009 mouse study, Japanese researchers found that black garlic was more effective than fresh garlic in reducing the size of tumors, for instance. The study was published in the journal Medicinal and Aromatic Plant Science and Technology.16 In another study, black garlic was found to have twice the antioxidant levels as fresh garlic—the aging/fermenting process appears to double the antioxidants.

Black garlic is packed with high concentrations of sulfurous compounds, especially one in particular: s-allylcycteine (SAC). Science has shown a number of health benefits from SAC, including inhibition of cholesterol synthesis. Perhaps this is why Mandarin oil painter Choo Keng Kwang experienced a complete reversal of his psoriasis after just four days of eating half a bulb of black garlic a day—this, after trying countless medically prescribed skin creams that were all complete failures.

An advantage of SAC is that it is well-absorbed and much more stable than allicin and 100 percent bioavailable. Researchers are confident it plays a significant role in garlic’s overall health benefits.17 Be mindful, however, that black garlic’s benefits may be more effective than fresh garlic for some conditions but not others, given its allicin content is low. For example, I suspect it may not be as effective if you have an infection, as allicin is thought to be the primary anti-infective agent in garlic, and fresh garlic is higher in allicin than black. According to Blue Fortune Farm (which admittedly sells black garlic), black garlic has the following favorable nutrient profile:18

  SAC (mg/g) Calcium (mg) Phosphorus (mg) Protein (g)
Black Garlic 5.84 36.66 80 12.5
Raw Garlic 0.32 5.0 40 2.2

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