To many of us in the region, bak kut teh, which is basically our version of bone broth, represents warm comforting nourishment in a bowl.

Ready-made soup packets containing dried ingredients for the peppery Teochew-style or Malaysian-style herbal broth are also readily available at supermarket shelves in Singapore and Asian groceries worldwide.

But is there now a need to slap health warning labels on your favourite bowl of bak kut teh?

Reports citing an Australian study published in the journal of Forensic Science, Medicine and Pathology last month claimed that there is a link between the ingredients found in herbal bak kut teh and varying degrees of liver damage — measured by the toxic response in liver cells.

According to a report in ABC News, the study was launched after a patient of one of the researchers was found to have suffered liver damage after eating bak kut teh while also taking Western medication to lower her blood lipid levels.

Another patient had also died from liver failure after taking a herbal mixture to treat inflammatory bowel disease.

The journal article stated that one of the reasons behind the study was to see if toxic liver disease (hepatotoxicity) could not only be caused by certain herbal products but also in dietary herbs consumed as food.

All four packets of bak kut teh herbs bought commercially which were used in the study were found to cause liver cell death to varying degrees. 

Speaking to ABC Radio Adelaide, one of the researchers, professor Roger Byard, shared that due to the vague terms used in the ingredients list, such as "spices, pepper and salt", it is unclear which specific ingredient is the likely cause.

But despite the seemingly alarming results, Byard doesn't see it as a cause for panic.

"Obviously, a lot of people have this soup and don't have a problem. In fact, I love this soup," said Byard, adding that he'd had it "for years".

He stated, however, that he has since stopped drinking it.

Interestingly enough, Byard shared with ABC Radio Adelaide that the formulation found with the most toxicity was a packet of bak kut teh taken out from his own pantry, "which was kind of disturbing".

Said Byard: "People say herbs are natural, therefore they're safe.

"But if anything has a therapeutic effect, it can have a therapeutic side effect and there's a whole lot of things that happen like herb-herb interactions or herb-drug interactions that we just don't know what's going on and that's the scary thing for me I think."

The study concluded by stating that more research would need to be conducted to evaluate the association between herbal soups and acute liver failure, especially for individuals with pre-existing liver disease.

'Bak kut teh cannot be poisonous'

One gastroenterologist AsiaOne spoke to, however, rejected the possibility of the herbal soup being poisonous to the body.

"Bak kut teh cannot be poisonous. Otherwise, we will see thousands of liver damage patients daily at our clinic. This is just common sense observation," said specialist Dr Desmond Wai in response to our queries.

Professing to love the dish himself, Dr Wai added: "If Prof Byard's conclusion is correct, I would have died of liver failure long ago."

Dr Wai took into consideration that the Australian research was conducted in-vitro (outside of a living organism), within the confines of a lab. This would not accurately replicate what would happen inside a human body.

"I always tell patients what we ingest does not equate to what their organs are exposed to, said Dr Wai, citing the example of how the soup would have to be digested and broken down as it travels from the stomach to the intestines before the molecules can be absorbed and transported to the liver.

"So after drinking bak kut teh soup, only the digested and absorbed molecules will touch the liver. The herbs and other ingredients in bak kut teh soup do not have any contact with our liver," he stated.

He stressed that the conclusion from this study "cannot be extrapolated into drinking bak kut teh soup and liver health".

Dr Wai however, agreed that certain herbs or foods can interact with medication to adverse effects — such as grapefruit, which can cause organ rejection in transplant patients. 

Supplements such as krill oil pills which contain antiplatelet agents may also lead to a higher risk of bleeding after an operation, warned Dr Wai.

He is also cautious when it comes to advising his patients on whether they are able to consume herbal or Traditional Chinese Medicine (TCM) products as "they may work, but they may also cause harm".

"I will never encourage them to take herbs as I have no knowledge of them," he shared, adding that patients should always let their doctors know if they are on any medications, be it TCM or herbal products.

Dr Wai also pointed us to a study he'd worked on, published in 2007, which found that traditional complementary and alternative medicine products accounted for "about 55 per cent of all cases of acute liver failure from drug-induced liver injuries".

TCM practitioners' take

According to a report by 8world, TCM practitioners whom they spoke to argued that the link between bak kut teh and liver damage would have to be substantiated further before a definitive conclusion can be made.

One TCM practitioner, surnamed Cao, noted that the common ingredients in herbal bak kut teh include angelica root, codonopsis and wolfberry, which are not known to be harmful to the liver. He noted that ingredients in the Teochew version of bak kut teh contains mainly pepper as well as garlic, which has antibacterial properties.

"Without obvious evidence, we can't put the blame on bak kut teh entirely," said Cao.

However, Cao added that he would generally advise those who enjoy eating herbal bak kut teh to treat the meal as a form of Chinese medication. And if one is taking Western medication at the same time, it would be best to leave an interval of one hour in between consuming either, he added.

There could also be other reasons for the results of Byard's study, said another TCM practitioner, surnamed Chen, who was also interviewed by 8world. 

She theorised that if the ingredient packets were improperly sealed, mould might have formed within. "Mould can affect liver function," said Chen, adding that whether people get sick from consuming mould would also depend on the individual's bodily resistance to mould.

Chen agreed that more thorough research would have to be carried out to determine the veracity of the findings.

About the study

In the Australian study conducted on liver cells in a lab environment, a total of four packets of store-bought bak kut teh ingredients were used.

The first packet contained dried hawthorn, the second, goji berries, ginseng, bark, and dried mushrooms. The third formulation contained the ingredients astragalus, polygonatum odoratum, ligusticum chuanxiong, codonopsis pilosula, cinnamomum cassia, angelica sinensis, Illicium verum, piper nigrum, and eugenia caryophyllata, while the ingredients in the fourth and final packet was simply listed as "spices, pepper, and salt".

The study found that all four broth packets produced significant toxicity when mixed with liver cells, with the fourth packet found to be the most toxic, resulting in 83 per cent cell death. It was also the only formulation of the four found to carry persistent toxicity (causing 15 per cent of cell death) even after the mixture was diluted 10 times.

The first formulation was found to be least toxic, with 21 per cent cell death observed, while the second and third packets were found to result in 30 per cent and 41 per cent cell death respectively.

candicecai@asiaone.com

For more original AsiaOne articles, visit here.