A new restaurant specializing in kimchi is about to open in my neighborhood. It is the first of its kind in my little corner of the world.
Nestled between a really good Hawaiian health food restaurant and an award-winning Indian restaurant, the obvious question is why choose kimchi? Apart from mixing things up a little and adding some variety to our culinary choice when dining out, is there any good reason to choose kimchi?
According to the flyers for the new restaurant, kimchi possesses anti-inflammatory, antibacterial, antioxidant, anticancer, anti-obesity, probiotic properties, cholesterol reduction, and anti-aging properties. Too good to be true? Time to do a little sleuthing.
What is Kimchi?
Kimchi is a popular traditional Korean food. Kimchi might be new in my world but kimchi was described as early as 1145 AD in an ancient Korean book entitled "Samkuksaki."
It is made by pre-treatment of oriental baechu cabbage, brining, blending with various spices and other vegetables, and finally fermentation by lactic acid bacteria (1).
The materials needed for kimchi can be divided into 5 main groups:
- raw materials (Chinese cabbage is most commonly used but other vegetables, including radish, young Oriental radish, ponytail radish, and cucumber are also used)
- spices (red and black pepper, cinnamon, garlic, ginger, onion, and mustard)
- seasoning ( salt-pickled seafood, corn syrup, sesame seed, and soybean sauce)
- other materials (carrot, leek, and water cress, seafood like oyster and shrimp, cereals like barley and rice, fruits like apple and pear, meats like pork and beef)
- salt for brining.
Slight variations in any/some/all of the steps of this process allow for variation in terms of the specific final content/nutritional value and taste of any batch of kimchi.
Lactic acid fermentation has been used as a way of preserving foods for over 1000 years. In times of old (and nowadays), food was harvested when it was abundant and fermented so that some of the food could be eaten at a future time of food scarcity.
There are other fermented foods in Korea, apart from kimchi, include chongkukjang, doenjang, ganjang, and gochujang (2). Kimchi is the most popular and the most commercially successful of these.
In homes and restaurants, the use of unsterilized raw materials leads to the growth of lactic acid bacteria ((Lactobacillus brevis, Lb. fermentum, Lb. plantarum, Leuconostoc mesenteroides, Weissella confusa and Pediococcus pentosaceus) which do the fermentation (3).
The commercial sector uses starter cultures in the manufacture of kimchi and sales of starter kits are rising worldwide (4).
Kimchi continues to ferment following production. This can lead to over-acidification which can shorten the shelf-life of the kimchi. Strategies to delay over-acidification of kimchi include adding ingredients such fruits or fruit seed extracts, extracts of medicinal herbs, culinary herbs and spices to kimchi (5).
The nutritional content of one commercially available kimchi is (per 100gm):
- Protein 0.97 gm
- Energy 34 kcal
- Fat 0.49 gm
- Carbohydrate 6.8 gm
- Fiber 1.9 gm
- Sugar 3.88 gm
- Calcium 39 mg
- Iron 0.70 mg
- Sodium 485 mg
- Vitamin C 11.7 mg and
- Vitamin A 728 IU (6).
Is There any Research?
At first, it looked like there were 1028 publications and 21 clinical trials relating to kimchi. To put this into context, there are 31,000 publications on fermented products including 189 clinical trials.
Actually, things get worse for kimchi. On closer look, there are a number of researchers with the name Kimchi who have conducted clinical trials. When we eliminate the clinical trials that have nothing to do with kimchi food (ie studies done by Dr Kimchi), we are left with just 5 clinical trials on kimchi. Not a great track record for almost 1000 years.
Does Eating Kimchi Help Increase Immunity?
A study published last year showed that Lactobacillus from kimchi relieved the symptoms of atopic dermatitis in mice (7).
Please forgive me, but I can't resist. Here is the conclusion of the second study relevant to kimchi and allergy that I found (8).
"E. faecium FC-K can be a beneficial probiotic strain that can modulate the Th2-mediated pathologic response."
I am afraid that even Google translate won't help us with that mumbo jumbo.
Here is my translation: "the study was done in mice and showed that kimchi caused some changes in blood tests that could possibly reduce allergic responses."
A study in 43 healthy Chinese college students was randomized to kimchi/not for four weeks followed by a one week wash-out period and then kimchi/not (depending on what they had been randomized to in the first phase of the study) (9). The study looked at measures of immune function but found that short-term kimchi had no effect on immune function.
Despite fancy-sounding studies, we have no actual proof that eating kimchi helps increase immunity. Quite the opposite. The available (totally inadequate) studies show that kimchi reduces unhelpful immune responses or does nothing at all.
Does Eating Kimchi Help Reduce Cravings?
No. There is no proof.
There is no proof that eating kimchi can help reduce cravings.
Does Eating Kimchi Help Fight Cancer?
A group of researchers deliberately induced stomach cancer in mice and evaluated the effect of a specially modified form of kimchi (10). The specially modified kimchi was comprised of mustard leaf, pear, mushroom, Chinese pepper, and sea tangle juice added to a standardized kimchi recipe.
The modified kimchi was found to have anti-cancer effects as compared to standard kimchi. Just to be clear, this shows that a modified kimchi had an anti-cancer effect in mice and not regular kimchi.
A similar type of study induced colon cancer in mice and found that kimchi protected against the development of colon cancer in this mouse model (11).
A 2014 meta-analysis from Korea showed that salt and kimchi were associated with a statistically significantly higher risk of stomach cancer (12). This 2014 study was consistent with the results of a 2005 case-control study from Korea which showed that kimchi and soybeans increased the risk of gastric cancer (13).
The data on kimchi and cancer is inconclusive and certainly does not prove that kimchi helps prevent cancer. It may even cause gastric cancer.
Does Eating Kimchi Help Improve Digestion?
No. There is no proof that eating kimchi helps improve digestion.
There is no proof that eating kimchi helps improve digestion.
Is Kimchi Good for Heart Health?
An actual real study (ie a study with real humans) investigated the effects of kimchi on lipid levels (15) . They compared the effects of low dose kimchi (15gm/day) versus high dose kimchi (210gm/day) in 100 volunteers. The study intervention lasted for seven days.
Both arms of the study were noted to have significant decreases in blood lipid levels. The effects were greatest in people who had high lipid levels at baseline and in study subjects who took the higher dose of kimchi.
A study in 21 participants with pre-diabetes compared fresh (1-day-old) to fermented (10-day-old) kimchi (16).The study involved randomization for 8 weeks to fresh or old kimchi, followed by a 4-week washout period, and then study subjects switched to the other type of kimchi for the next 8 weeks.
The study showed that both types of kimchi significantly decreased body weight, body mass index, and waist circumference. Fermented kimchi decreased insulin resistance, and increased insulin sensitivity. Systolic and diastolic blood pressure decreased significantly in the fermented kimchi group.
In a similar study, 22 overweight and obese patients were randomly assigned to two 4-week diet phases (fresh and fermented kimchi) separated by a 2-week washout period (17). During each diet phase, the subjects consumed either fresh or fermented kimchi. Significant decreases in body weight, body mass index, and body fat were noted in both groups.
Blood pressure, fasting glucose and total cholesterol showed statistically significant decreases in the fermented kimchi group as opposed to the fresh kimchi group.
Kimchi shows benefits for heart health in a handful of small studies.
Is Kimchi Good For Oral Health?
A study of 32 patients hospitalized at a long-term care hospital in Korea looked at kimchi for oral health (18). The study compared the effect of kimchi to chlorhexidine solution (0.12% dilution).
This was not a blinded study. Each patient received chlorhexidine twice daily for one week, followed by a gap of two weeks, followed by kimchi twice daily for one week. Scoring using a vaildated score for oral health showed no benefits of kimchi but patients reported improved oral health with kimchi.
The results of a short clinical trial looking at kimchi versus chlorhexidine for oral health were confusing and inconclusive.
Is Kimchi Safe?
There is very limited data on the safety of kimchi. Possible concerns about the long term risks of stomach cancer have been mentioned already.
During the manufacture of kimchi, putrefactive bacteria die off and leave good bacteria (19). At least, that is the theory.
Studies have shown that bugs that can cause human illness such as E coli and Salmonella can survive the fermentation process (20). Fermentation temperature and time are the critical factors to control pathogenic (disease-causing) bacteria.
Kimchi contains salt and this is a factor to consider in people with kidney disease or high blood pressure. Kimchi with lower salt content would be preferable in terms of salt load.
Alcohol is a natural by-product of fermentation. The alcohol content of kimchi is too low to cause intoxication and as such is usually considered to be halal.
I was a little excited (and a tad confused) when I came across a 2018 publication entitled:
'Effects of Kimchi on human health: A protocol of systematic review of controlled clinical trials' (21).
Did this mean that someone else had done all the hard work on kimchi?
Had these authors stumbled on some gems that I had missed?
Turns out that this paper is just an expression of intent to do a systematic review in the future. I feel it only fair to tell these enthusiastic researchers that with just 5 clinical trials to work on, this is not going to be the publication to launch their careers. (Sorry, but I have spent years supervising PhDs and have a good sense of what type of research launches a career).
Why then do blogs make health claims about kimchi?
These blogs are (if I may say), "liberal, in their interpretation of the data.
They figure that:
if kimchi contains ginger and
if ginger has the following health benefits
then kimchi automatically has the same health benefits.
Same for peppers and chilies, etc.
As we have seen, kimchi content can vary wildly. This means that any particular batch of kimchi may/not have ginger/pepper/chili etc.
Let's be generous and say that the batch of kimchi does contain ginger/pepper/chili, but still the "dose" of ginger/pepper/chili required to have a medicinal effect may not be anywhere close to the level in any batch of kimchi.
Kimchi looks good for cardiac and maybe metabolic health which means that my patronage of the new kimchi restaurant will be based on trying out something new but I won't be fooling myself that I am at a health-food restaurant.