Does Garlic Cause Cancer When Heated

I write this comment below to a request and question via Whatsapp on a video narrated  in Chinese Mandarin. It was sent to me for advice by a friend called Sister Sonia Soon from Bahhma Kimaris on behalf of her sister and someone else from a cancer society (CanSurvive) in Malaysia

They solicited my opinion that garlic when overcooked causes cancer

Dear sister Soon

Thank you sister Soon for soliciting my personal view once again on this video claim

This video in Chinese Mandarin emphasizes on overheating the garlic (Allium sativum) that it claims can cause cancer, but it says garlic is cancer-protective if eaten uncooked.

If you were to solicit my opinion on this, let me tell you a lot of foods containing complex starches such bread when toasted, cakes, traditional kuih, coffee (after roasting its beans), potatoes chips, pop corns, fried rice, fried mee, fried rice noodles and any foods containing starches (almost all foods do) when cooked above 120 degrees Celsius produces  this acryloyl group called acrylic amide or acrylamide or prop-2-enoyl  in short

We are not too clear on the mechanism how this substance is formed when almost all starchy foods,  not just garlic alone, are heated to above 120 ⁰ C. Food scientists  think this may be a by-product of Maillard reaction.

Maillard reaction:

Maillard reaction is a chemical reaction between amino acids and reducing sugars that gives food its brown colour and distinctive flavor when foods like bread, buns, and cakes are heated at a high temperature. It is a non-enzymic browning reaction, a very well-known reaction in food chemistry.

This reaction does not occur when starchy foods are boiled such as in boiled potatoes and rice. But in fried or baked goods, acrylamide may be produced by the reaction between asparagine (an amino acid from protein) and reducing sugars (fructose, glucose, etc.) or by reactive carbonyls at temperatures above 120 °C.

Unfortunately some later studies  showed that  acrylamide was also present  in black olives, prunes, dried pears for reasons not clear to us.

The Decomposition of Acrylamide:

However, we also know that acrylamide decomposes in the presence of acids, bases, oxidizing agents, iron, and iron salts. This means that even if starchy foods are baked, acrylamide may not be present if they are cooked at high temperatures in the presence of vinegar (acetic acid), lime juice (citric acid) or if baking powder (sodium bicarbonate, a mild alkaline) has been added.

The baking powder itself will decompose into carbon dioxide and sodium carbonate which is even more alkaline than baking powder. This may block the formation of acrylamide, but we need studies to show this.

But even if acrylamide is present, this compound can decompose even without heating into ammonia, and with heat, it decomposes into carbon monoxide, carbon dioxide, and oxides of nitrogen after some time. Again we need to conduct studies on this.

Discovery of Acrylamide:

Acrylamide was discovered in April 2002 by a scientist in Sweden when she found the chemical in starchy foods, such as, French fries (potato chips), and bread that had been heated higher than 120 °C, but  was not found in food that had been boiled or in foods that were not heated.

The discovery of acrylamide in some cooked starchy foods provoked worries about the cancer-causing effects of these foods.

However as today (Friday, June 1, 2018), food scientists, nutritionists, toxicologists, and medical scientists are still uncertain whether or not acrylamide in foods put us all at risk of developing cancer.

Tumors in Experimental Animals:

In experimental animals, exposure to acrylamide was shown to causes tumors in the lungs, thyroid, adrenal glands, and testes.

This concern is not just through ingestion, since acrylamide can easily be absorbed by the skin and distributed throughout the body.

It was demonstrated that the highest levels of acrylamide after exposure were found in the blood, non-exposed skin, liver, the kidneys, in the testes, and spleen.

The mechanism how the carcinogenicity of glycidamide is triggered in animal models is through a gene called cytochrome P450 which transfers its metabolism into a genotoxic metabolite called  glycidamide.

However, people who worked in food manufacturing industry and were exposed to twice the average level of acrylamide do not exhibit higher cancer rates. 

Detoxification of Acrylamide:

Interestingly, acrylamide and glycidamide can also be detoxified by conjugation with glutathione (an antioxidant produced by the body) to form isomeric glycidamide-glutathione conjugates, and these  are subsequently  metabolized to mercapturic acids and excreted harmlessly in the urine.

Neurotoxic Effect:

Acrylamide has also been found to have neurotoxic effects in humans who have been exposed. Animal studies also show the same neurotoxic effects.

Nonetheless, we cannot translate experimental results based on animal studies into human.  First of all, human life span is far longer than smaller animals like rats, rabbits and guinea pigs.

Secondly, the dose normally given to animal models are far higher and fed continuously than those consumed unintentionally by human in their daily diet.

What we are unsure of is the accumulative effects of acrylamide in humans even at low doses, but over a long period of our  life span. So far we have no evidence on its correlation with cancer in humans

Nutrigenetic:

Thirdly, how our human body reacts to acrylamide and other substances may not necessary be the same as those in animals. There are a lot of other factors such as nutrigenetics to be considered.

Nutrigenetics is a sub-specialization of the science of nutrition on how nutrients have variations in  genetic responses, and thus the onset of disease and their outcome such as cancer.

Food substances such as acrylamide may influence gene expression and gene behavior and also their epigenetics. The branch of molecular medicine called epigenetics refers to external modifications to DNA that turn genes "on" or "off."

These modifications do not change the DNA sequence, but may trigger off disease like metabolic syndrome and cancers, and the way we respond to acrylamide or other poisons are different from individuals to individuals, not just among human or among animals, but even among individual humans.

In short, you and I are entirely different even though we share almost exactly the same genome, and we respond to disease, their treatment including cancer and their outcome differently.

Absorption through Skin:

  

Acrylamide has been found to be a skin irritant. Thus being a chemical irritant, this may act as a tumor initiator on skin tissues, giving an increased risk to skin cancer. Clinical presentations of acrylamide exposure include dermatitis in the exposed area, and subsequent peripheral neuropathy.

But what we are concern is not so much  the presence of acrylamide in heated garlic, but by the loss of a lot of valuable suphur-containing allicin and other functional active components in garlic,  one of the most important medicinal principle is ajoene when garlic is cooked at home,  or processed into pills by other means through food technology

Allow me to briefly explain  this in a simple language for the benefit of my gentle lay readers.

Ajoene:

Ajoene has medicinal properties. It is an antioxidant that is able to block the formation of free radicals like superoxide. Ajoene also acts as an antithrombotic agent that prevents platelets in the blood from forming blood clots. This means that regular consumption of raw garlic reduces the risk of heart disease and stroke in humans due to blood clots

Ajoene processes anti-viral properties against a number of viruses such as those that cause vesicular stomatitis, para-influenza, vaccinia virus, human rhinovirus, and herpes simplex.

It was shown that when cells are infected by a human immunodeficiency virus (HIV), ajoene in garlic was able to block the integrin-dependent processes as shown by Tatarintsev AV, et al.

Ajoene also exhibits broad-spectrum antibacterial and antifungal properties, and garlic has been used traditionally as a natural antibiotic and fungicide against many types of infections since ancient times by all civilizations for thousands of years.

Phyto-dynamics:

The mechanism how ajoene acts as natural antibiotics is its ability to inhibit genes expression controlled by quorum sensing.  Quorum sensing is a communication system used by pathogenic bacteria like Pseudomonas aeruginosa to synchronize the expression of specific genes involved in pathogenicity.

Cancer therapeutics:

In cancer therapeutics too, ajoene has been found to exhibit anti-leukemia properties against acute myeloid leukemia and it was found to decrease basal-cell carcinoma tumor size by inducing apoptosis (induced cell suicide)

This was shown that ajoene was able to effectively inhibit tumor cell growth by targeting the microtubule cytoskeleton of cancer cells and through other phyto-pharmaco dynamics.

  

Like its action against pathogenic microorganisms, in cancer management where gene expression, epigenetic, and nutri-genetic are of paramount importance to our understanding on the biology of malignant growth and their spread, garlic and other natural medicines are of current interest to  scientists in their search for cancer treatment.

Garlic Pills vs. Raw Garlic:

Unfortunately this extremely useful cancer fighting and cardio-protective sulphur-containing ajoene in garlic was found to be absent in all 20 brands of garlic pills manufactured by 20 different countries

This strongly suggests to us that when foods are processed by extraction, heating, cooking or by other means, a lot of valuable nutrients and medicinal properties are lost.

Hence, as a general rule, wherever, and whenever possible, bearing in mind hygiene, digestibility, toxicity and other factors when some foods are consumed raw, plant-based foods generally are best consumed raw or lightly cooked such as in blanching of vegetables where most of the nutritive, medicinal and health-protective properties are retained

By lim ju boo