Last Updated on June 25, 2023 by Art

Good News for Cancer Prevention!

Heads of garlic

Garlic and its cousins occupy a unique position, straddling the worlds of superstition, medicine and the culinary arts. In modern cookery, the most familiar Alliums, that is, the garlic family, are onions, garlic, scallions, shallots, leeks and chives.

Here’s a roam through garlic’s history, its science and its practical benefits.

Garlic: Food for Healthy Supermen

Onions

How much did the Ancients know, anyway? This is an intriguing question where alliums are concerned.

The Egyptians fed garlic to laborers to improve their strength and endurance. This food was of such practical value that it was used for barter: 15 pounds would buy a healthy male slave for work on the pyramids. We don’t know whether the upper classes also consumed it. However, when King Tutankhamen’s tomb was opened in 1922, there were cloves of garlic inside.

The Greeks and Romans copied this custom and enlarged upon it. Soldiers and Olympic athletes ate garlic for performance enhancement. In addition, the physicians Hippocrates and Dioscorides also used it to treat tumors, pneumonia, indigestion, respiratory problems and even pimples.

In Judaism, eating garlic is a “mitzvah,” a religious good deed. Rabbis advocate that “it satisfies one’s hunger, it warms the body, brightens the face, increases semen and kills stomach lice.” It’s hard to beat all that!

Healers in China used garlic for indigestion, and in India for heart disease and arthritis. However, the Indians did not view it as an unalloyed boon. Buddhists and Hindus who follow a strict diet exclude the alliums because they stimulate the body and distract from meditation.

Today, researchers are vigorously pursuing the health benefits of the alliums. However, to my knowledge they are not spending much time studying strength, endurance or lice.

Garlic: Destroyer of Vampires

Vampire

A tale from the prophet Mohammed says that when Satan was expelled from Eden, garlic sprang from his left footprints and onion from his right ones. With this sort of origin lore, it’s not surprising that myths abound about the alliums.

One of the most prominent legends is associated with Romania and was popularized by Bram Stoker’s Dracula. The plot features garlic’s amazing power to repel and to immobilize demons and vampires.

In many cultures from the Greeks to present-day, people credited garlic with the power to ward off the Evil Eye, a magical manifestation of hate. At the same time, throughout these years and nations, many societies have enthusiastically incorporated alliums into their diets! A purity vs evil dichotomy for sure…

Of course, there’s a sense in which wearing a garlic necklace, or having garlic on your breath, could protect your health. If your aroma keeps other people at a distance, you’re less likely to catch their germs. If they too reek of garlic you will not scare them away. However, perhaps you and they are already friends, and have antibodies against each others’ germs!

Applying Science

Scallions

Meanwhile, scientists have not been asleep. There’s a well-established method for vetting the possible health benefits of different personal habits, including diet:

• Epidemiology: Look for inverse associations between allium consumption and various diseases. That is, if you eat more garlic, you may have less chance of heart disease, cancer and so forth.
• Proportionality: In addition to associations, researchers want to see whether there is a “dosage effect.” In other words, how strong is the curative effect as a function of the amount or frequency of alliums eaten?
• Mechanistic Studies: Scientists always want to know “why” something works before they believe they understand it. So a necessary next step is for someone to propose a mechanism for garlic’s effects, such as how some chemical component of the plant affects one or more steps of cancer growth. Then, to run experiments to prove or disprove the hypothesized process.

Basically, it’s not enough to know that eating garlic may be good for you. Researchers want to understand everything about how it may work. That info will provide assurance of the validity of health claims. It also helps us know about limitations and potentially undesirable side effects.

Garlic: A Cure For Many Diseases – Maybe

Shallots

There’s a huge amount of scientific (and non-scientific) literature about garlic. Most of it is positive, either slightly so or substantially.

I’ll offer you a couple of sources, then give my bottom-line summary:

• A 2014 Bon Appetit article summarizes 4,000 years (!) of studies. They embrace these areas: heart disease; cancer; colds & flu; sexual health & fertility; weight loss; bites of insects, snakes & dogs; anti-bacteria; Alzheimer Disease; and diabetes. This article is overwhelming in its number of examples.
• A 2016 article is a deep technical review of cancer prevention research for all the alliums, especially garlic and onions. This article overwhelms in another way, with 96 citations.

Here are my conclusions from these and a large number of other articles:

• Cancer – Strongest Evidence: Alliums help prevent many types of cancer, specifically gastrointestinal (colorectal, stomach, esophagus) and (newly proven) breast cancer. They block the formation of nitrosamines from nitrites/nitrates, reduce cell proliferation, enhance DNA repair, induce cancer cell death and stimulate the immune system. Studies show that people who consume large amounts of alliums (7 portions or more per week) have a 25% to 80% reduced chance of contracting most types of cancer.
• Heart Disease – Good Evidence: Garlic helps keep the cardiovascular system healthy. However, it also thins the blood. Consult your doctor before taking large amounts of garlic if you also take a blood thinner or frequent aspirin. And beware: garlic in large doses can cause fatal anemia in pets.
• Dementia: Several studies suggest that aged garlic extract may lower the risk of Alzheimer Disease and dementia. Researchers aged the herb for 20 months at room temperature to convert volatile components such as allicin into a stable chemical, SAC (S-allylcysteine).
• Antibiotics: Garlic extracts may act as antibiotics against certain bacteria, help cure colds and flu, and keep away mosquitoes.

How Much Is Too Much?

Leeks

The evidence is still coming in, but in general, the alliums appear to be good for human health. Many folks believe, if a little is good for you, a lot must be better. So let’s see how much might be too much.

One way to determine a safe quantity of garlic is to look at the doses in medical research studies. Researchers don’t want to poison their test subjects, so we can usually trust them to use safe quantities of garlic.

Unfortunately, many research studies don’t use garlic itself. Instead, they use commercial garlic products or some sort of garlic extract. So I focused on studies using garlic or garlic powder. Here are dosages used in studies lasting for 4 weeks or longer: 0.9 grams/day (athersclerosis); 1.5 grams/day (diabetes); 1.2 grams/day (high cholesterol); 1.5 grams/day (high blood pressure); 1.2 grams/day (prevent tick bites). In other words, researchers have not hesitated to administer up to 1.5 grams of garlic per day to a test subject.

Unfortunately, this is a miniscule quantity of garlic. An average supermarket garlic clove weighs 4 to 7 grams. If a person wanted to test the healthfulness of garlic, it’s hard to imagine them consuming less than one clove per day!

            Bring In the Rats!

There’s another way to decide how much garlic may be safe to consume. In 2006, a group of researchers in Chandigarh, India fed rats a wide range of garlic doses. The daily doses ranged from 0.1 to 5 grams per kilogram of body weight, continued for 28 days. For an 80 kg (176 pound) human, this would amount to 8 to 400 grams, or 1.5 to 73 cloves of garlic per day.

The experimenters were particularly interested in measuring liver function and observing tissue changes in the rat livers. All the rats showed some decline in liver function but no histological changes for doses of 0.1 and 0.25 g/kg. The researchers concluded that these lower doses are safe because they did not lead to visible changes in the liver.

Now we may well question whether a rat’s ability to tolerate garlic has anything to do with human beings. We might also question whether a dose that impairs liver function is nonetheless “safe” because visible changes in liver tissue do not result. However, if we take the study results at face value, we would conclude that a human can safely consume 20 grams of garlic, or 4 cloves per day, every day.

            Back to the Humans, Please

American Family Physician proposes a safe level of consumption that’s slightly less than the rat study. They suggest 4 grams of garlic per day, which they compute as 1 to 2 cloves per day. When we consider that in China the per capita consumption is 37 grams, or 6.75 cloves per day, a guideline of 1 to 2 cloves per day for a healthy adult seems safe and conservative. The World Health Organization has in the past specified a daily dose of 2 to 5 grams of fresh garlic. See also WHO’s articles on garlic. And if you only cook with garlic once or twice a week, you can easily eat several times this when you do use garlic.

How To Get Maximum Benefit from the Alliums

Garlic

Here comes the practical advice. And it comes in two flavors: (1) how to retain the healthful chemicals in the alliums during food preparation; and (2) how to counter unpleasant side effects from the food.

            Keep the Healthy Biological Elements

• Eat the Whole Enchilada: Alliums, like many herbs, contain hundreds of chemicals. We think that the healthiest component is alliinase. Alliinase is released from the cells upon chopping or crushing. It reacts in the air to produce allicin and other thiosulfinates. It is these that we believe have the strongest effects on health. However, the strongest evidence for the health-giving effects of alliums comes not from dosing with specific chemicals, but by studying the consumption of garlic, onions and so on in the diet. Until we fully understand the mechanisms, especially cancer prevention, don’t limit yourself to a single component. Use the entire herb in your diet!
• Wait Before Cooking: When you peel, mince or crush garlic or onion the aliinase begins to react with the air. If you immediately cook the vegetable, the heat deactivates the aliinase and you don’t derive its health benefits. After exposing to the air you should wait before cooking. How long should you wait? It depends on which source you listen to. Witchipedia says 20 minutes. 10 minutes, say some researchers. Personally, I vote for 15 minutes, which also agrees with other studies.(1, 2)
            Digression: You may know the famous recipe, Chicken with 40 Cloves of Garlic, often attributed to James Beard. The Barefoot Contessa and the New York Times also give versions of this dish. You can improve the healthfulness of all such recipes by peeling the garlic cloves and letting them “rest” for 15 minutes before they see any heat.
• Reach for the Spice: Among the alliums, the more pungent the vegetable, the higher the concentration of aliinase in the cells. Therefore, it’s not surprising that garlic and onions have been the most studied, and chives the least. If you want the health benefits, pungency is your key.

            Countering the Downsides

• Garlic Breath: One of the unwanted side effects of consuming the most pungent of the alliums is stinky breath. This effect is greatly reduced if you cook the herbs (after letting them “rest”) before eating them. Food experts also recommend clearing the breath by chewing fennel seeds, or munching parsley or fenugreek.
• Indigestion: Pungent alliums, especially raw ones, can startle your stomach. So it’s best to eat them with other foods. Even so, some people still get indigestion from alliums because they are high in FODMAPs. Those are carbohydrates that ferment in your digestive tract, causing gas and stomach pain. The PaleoLeap site gives this recipe to avoid indigestion: crush the garlic cloves; let them sit for 5 to 10 minutes; fry in hot oil; remove the garlic & discard it, but then cook with the allicin-saturated oil.
• Blood Thinners: We have already noted that garlic tends to thin the blood. This can enhance the effect of blood thinners and regularly-taken aspirin. If this applies to you, or if you have blood clotting problems, you should consult your doctor before taking extra garlic for your health.

What are you waiting for? Toss garlic, onions and other tasty alliums into your favorite recipes and enjoy these healthy foods. Just be sure to let the peeled or crushed ingredients “rest” before cooking!

Image Credits:
Lead photo by Art Chester, of garlic grown by Rich Luther.
Other images from pixabay contributors: Bru-O (onions); kalhh (vampire); MikeGoad (scallions); Hans (shallots); manfredrichter (leeks); and johnoghue (garlic).