Garlic

Pauly in prison, using a razor-blade to slice garlic "so thin", we are told,
"that it used to liquify in the pan with just a little oil." (Goodfellas, 1990)
I can do this too, now that I shave like a Wise guy. 

Is garlic good for you? Or is that a stupid question?

I mean, I know it was eaten by Egyptian laborers who built the pyramids and the Olympic athletes of ancient Greece for strength. And granted, some French convicts who had been sentenced to death by grave-digging in the 18th century apparently used it to foil the plague; soldiers during the second World War (during which it was sometimes called "Russian Penicillin") used it to battle gangrene; and Chinese healers have traditionally recommend it for diarrhea, internal parasites, and poison. It was also given to me - raw, crushed, and coated with honey - whenever I got sick as a child growing up on the west coast of North America.

But while the unending litany of happy effects that have historically been attributed to garlic might seem to suggest that my question is indeed a stupid one, upon reflection it occurred to me that I would be equally astonished to discover that half of these claims are well-founded, as I would be to find that half of them are not.

And so, as a fan of being astonished, and also because it's garlic season, I have stubbornly decided that this stupid question is indeed ripe for investigation. Gather 'round, dear readers, and allow me to share with you the vegetables of my labor.

DEVILISH DETAILS

Domestic garlic (Allium sativum) and onions are fairly closely related; and among their more interesting family resemblances is an enzyme called alliinase, which, like a terrible secret, they keep well hidden until rage interferes with their better judgment.

The main evolutionary 'purpose' of alliinase appears to be to provide the plant with protection against predators. When the flesh of an onion or clove of garlic is injured - whether by bacteria, an animal, or an animal with a garlic-press - the alliinase in the damaged cells is spilled, and is thus brought into contact with other cellular components, producing chemicals that are meant to keep the offending organism at bay. By this ingenious means, plants can use unstable and dangerous chemical deterrents without having to continuously manufacture them, and while minimizing the risk of accidental self-mutilation.

(Interestingly, this clever tactic was independently developed by the common ancestor of  modern horseradishes and wasabi in a very striking example of convergent evolution. This should give pause to anyone who has taken the spiteful temperament of garlic and onions as biological evidence for the Christian myth that they originated in Satan's footprints as he strolled through the Garden of Eden.)

In onions, alliinase participates in the reaction that is responsible for their annoying ability to make you 'cry' while you butcher them.

In crushed garlic, however, this enzyme mainly produces a pesticide called allicin. It is allicin that, by most accounts, is "garlic's main biologically active component"; and it is allicin that has long been assumed to be largely responsible for garlic's medicinal reputation.

THE RISE AND FALL OF ALLICIN

Allicin, like most pesticides, is primarily meant to murder other organisms - or at least to get all up in their face; and apparently it does this quite well. For example, "in vitro" (or: "in test-tubes") allicin has been shown to have inhibitory effects on a "wide range of microorganisms including bacteria, fungi, protozoa and viruses", many of which can parasitize the human body.

But this is because the toxicity of allicin (despite being completely 'natural') "is rather high", as evidenced by the chemical burns it can cause when applied to the skin. It also has as strong odor, and inanimate objects it is applied to tend to acquire a garlic-y smell. Moreover,  the allicin molecule is actually quite unstable, meaning it tends not to stick around for very long unless it is properly extracted, suspended in solution, and stored in cool conditions. Mainly because of these facts, allicin has not seen widespread use as a topical "antiseptic" or as a "disinfectant", although this could change now that allicin has displayed effectiveness against the dreaded multi-drug resistant strain of the bacterium S. aureus (or "MRSA"), that has been terrorizing modern hospitals.

What about eating allicin? 

Garlic is sometimes eaten in the hopes that the allicin it contains will act against internal parasites. Allicin is also often touted as a heart-friendly, cancer-fighting "antioxidant"; and this claim, too, seems to be well supported by in vitro studies.

On the other hand, it turns out that allicin is also sensitive to heat, and is rapidly destroyed when cooked.

And even before you down some raw garlic in the name of good health (as, unfortunately, many do) you might care to note that what happens in vitro does not necessarily happen inside you; and that the antimicrobial properties that allicin demonstrates in test-tubes "may not be demonstrated in the body upon consumption." Indeed, it has been seen that allicin naturally decomposes "within sixteen hours" at room temperature; and much faster in the significantly warmer human stomach, where it is also exposed to gastric juices and given a wide selection of substances to react with. In fact, it appears highly doubtful that significant quantities of allicin make it into the small intestine even when consumed in the form of raw, freshly crushed garlic.

Still, things do not magically disappear when they "decompose", but rather break down into more stable molecules. In the case of allicin, decomposition apparently results mainly in the production of diallyl disulfide (DADS), which is used industrially to flavor food and is the predominant active ingredient in distilled garlic oil; and allyl mercaptan (AM). No product of its decomposition appears to be the in vitro 'wonder drug' that allicin is, but neither are they pharmacologically inactive, and at least they can make it into the gut.

However, precious few of the metabolites of allicin are what scientists call "bioavailable", meaning that they are either not absorbed by the digestive tract, or are immediately filtered out of the blood by the liver - leaving us to wonder how they could then possibly bind free radicals and fight tumors in the body as they might in the test-tube.

(Despite this, and despite the fact that few if any of them actually deliver allicin to the gut anyway, sales of allicin-containing supplements continue. Some of these use "enteric coated" capsules that protect their contents from stomach acid and release them in the small intestine. But even then they appear largely ineffectual. In any case, even if you find some that really work, there is good reason to suspect that these could do more to harm than good [remember, allicin causes chemical burns when applied to the skin for Christ's sake]. Just to be safe, therefore, I highly recommend asking a doctor before swallowing "allicin-containing" supplements.)


All of these complications, as well as the observation that allicin could not be responsible for the alleged benefits of the various forms of garlic (like garlic oil and Aged Garlic Extract [AGE]) that are known to be devoid of it, has caused the presence of allicin in garlic, once hailed as scientific proof of its "healing power", to be increasingly denounced as a red herring. 

THE OTHER GUYS

However, the fall of allicin has done little to dampen garlics reputation as being particularly healthful. Instead, garlic enthusiasts have concluded that "other compounds must be responsible for the benefits of garlic"; or to postulate that "a synergism" arising from their unique combination endows garlic with special properties that the study of no individual component can appreciate.

In fact there are literally hundreds of distinct substances found in garlic. What's more, an intimidating number of these are apparently capable of various pharmacological activities. Considering this, it is hardly surprising that while some studies have shown that garlic-derived compounds can engage in a degree of "concerted action", others have noted their "apparently opposite biological effects". From where I sit, this doesn't suggest 'synergism', but one of the major drawbacks of using unrefined herbal remedies in general.


In any case, these  hypothesis take for granted the very assumption I am now questioning; that garlic really is good for you; and so are of little value for my purposes here. Instead, I want to know if this assumption is founded in more than just folklore.

THE STINKING SCIENCE

I have heard it said that research into widely available herbal remedies is rarely done because pharmaceutical corporations don't want the public to have access to cheap and effective healthcare against which they would then have to compete. If there is indeed any truth to this claim, garlic has been a notable exception. Inspired by "its widespread health use around the world", scientists appear to have extensively studied the potential of garlic for use against quite a number of medical complications ranging from infectious to cardiovascular to oncological diseases. In fact, by some accounts the scientific investigations number in the thousands. But do these really support the claim that garlic has "known health benefits"?

>The Common Cold: One study of "reasonable quality" recently showed that one garlic supplement per day (which contained allicin), for whatever reason, really did help people to avoid the common cold. 

While this very interesting finding certainly suggests that garlic is "good for you", on its own it provides little reason to assume it. It is not known why this might be, and as far as I can tell, this result has not been independently reproduced to date.

Another thing this study fails to do is justify the fact that I was recently admonished for recommending "liquids and rest" in the place of "ginger and garlic" to a young lady who was just beginning to suffer cold-like symptoms. Let me be clear: the claim that garlic can be eaten to treat a cold is an entirely separate claim; and it appears to be largely based on hearsay. I can't find any good evidence to suggest that you should push garlic - raw or otherwise - on cold and flu victims who are already in a state of suffering.

It seems to me as though this idea has arisen out of the notion that garlic "boosts" or "kick-starts" your immune system, as Meghan Telpner informs us in her video series Making Love In The Kitchen (funky tunes at least). In fact, these statements are misleading in both their language and their meaning: as anyone with an auto-immune disorder knows, a "boosted" immune system is not necessarily a good thing; and there is little to no evidence to suggest that it whipped into action by garlic.

Furthermore, it seems to me that this widespread over-simplification is nontrivial, as it can obscure the difference between garlic as a healthy addition to the diet and garlic as "nature's panacea".

>Hypertension: Some positive results, but it seems more accurate to say that studies of the alleged ability of garlic to lower blood pressure have so far revealed an inconsistent effect. Also, a small but respectable clinical trial found "insufficient evidence to recommend garlic intake" to prevent pre-eclampsia (or pregnancy-induced hypertension) which afflicts "2-8% of [pregnant] women", and can sometimes be fatal.

>Cholesterol Management: A lot of people were quite excited about the possibility that garlic might help lower blood cholesterol and thus the risk of heart disease. Over 100 nonhuman trials tended to be positive. But despite this promise, the biggest and best studies of people have so far proven a real buzz-kill on this score. Unfortunately, although this idea isn't yet dead, it's doing a fair job of dying.

>Gastric Cancer: Observational studies have shown high garlic consumption to be correlated with a decreased risk of  stomach and colon cancer. But more studies are needed to solidify this evidence, and it is not known how garlic might be helping, if indeed it is.

>Thrombosis: Garlic apparently acts as a modest "anticoagulant", thinning the blood and prolonging bleeding time. This can be a good thing in certain situations, such as when blood starts clotting internally, but it is dubious as evidence that garlic is always good for you.

* * *

Few if any claim that moderate amounts of garlic in the diet is bad for your health. But, like Paul Bergner, author of the annoyingly-titled 1996 book The Healing Power of Garlic: The Enlightened Person's Guide to Nature's Most Versatile Medicinal Plant, many feel that the folklore surrounding garlic remains "the most powerful testimony to its effectiveness". Personally, however, I have concluded that although the evidence to date suggests that some garlic in the diet might well be "good for you", going much further than this involves treading ground that is currently too shakey; and I also feel compelled to mention that, like most things, there are drawbacks associated with its over-consumption, including but not limited to headaches, nausea, and digestive irritation (Bergner).

My view is that the potential of garlic as a food or spice as well as as an antibiotic is more than enough to explain why garlic has historically been held in such high regard (despite only peripheral awareness of the microbial world); and I can easily envision how these properties alone might have contributed to garlics formidable reputation as a medicine. Furthermore, the human bias toward perceiving false positive results, and the complex, variable cocktail of biologically active ingredients that is found in garlic are likely to have conspired in support of it.

To me, this possibility puts the unquestioning acceptance of folklore as a "powerful testimonial" to the "healing power of garlic" in rude perspective, although I admit that I may not qualify as an "enlightened person".


In any case, I believe I am capable of understanding why so many seem to perceive modern science to be only slowly and reluctantly "catching up" with ancient wisdom; and why herbal medicine enthusiasts might resent the fact that "the scientific establishment ... is often skeptical about the value of non-pharmaceutical substances" (Bergner). 

On the other hand, this suggests a virtue of skepticism, and indeed of asking seemingly stupid questions in general: as Richard Dawkins noted in The Oxford Book of Modern Science Writing (2008),

"science doesn't have all the answers, but it is good at spotting the important questions when they are camouflaged against a background of common sense."