Kimchi: a blend of fiber and beneficial bacteria

Kimchi is a traditional Korean side dish, typically made from cabbage or radishes depending on the recipe.^1–3 
Historically, it was prepared in winter using lacto-fermentation—a clever way to preserve vegetables for long periods.⁴ The cabbage is soaked in brine (a mixture of water and salt) for several weeks, allowing lactic acid bacteria to multiply. By producing lactic acid, these bacteria give kimchi its tangy flavor while naturally preserving it.⁵ 
It shares a resemblance with European sauerkraut—salted, fermented cabbage—though the type of cabbage and spices used are quite different.⁶ Kimchi is so deeply woven into Korean culture that Kimjang—the communal tradition of preparing vast quantities of kimchi for the winter—was inscribed on UNESCO’s List of Intangible Cultural Heritage of Humanity in 2013. 

Cabbage + fermentation = a plateful of health benefits

Since it’s made from cabbage, kimchi is low in calories (18 kcal/100g) and rich in beneficial fiber. It also contains a range of compounds characteristic of the Brassicaceae family (the large family that includes cabbage, turnips, radishes, and mustard), whose health benefits may be almost as impressive as their tongue-twisting¹⁽¹⁾ names.^2,4
Kimchi also provides several vitamins—notably A, C, B1, and B2— as well as minerals—calcium, potassium, iron, and phosphorus.^2,4
The health benefits of this Korean dish do not come from cabbage alone, they may also be attributed to the fermentation of the cabbage⁶ : compared to fresh cabbage, kimchi (fermented cabbage) has been associated with reductions in blood pressure, body fat, fasting blood sugar and total cholesterol… although these findings should be taken with a pinch of salt: the study involved only 22 people.⁸ 
Fermentation also enriches kimchi with live lactic acid bacteria, notably the genera Lactobacillus, Leuconostoc and Weissella , along with the valuable metabolites they produce.^2,4,5,7
For example, eating kimchi appears to be associated with an increase in gut bacteria known for producing short-chain fatty acids (sidenote: Short chain fatty acids (SCFA) Short chain fatty acids (SCFA) are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are involved in communication between the intestine and the brain. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. ) —molecules recognized for their beneficial effects on gut health and metabolism—and with a reduction in far less desirable bacteria, such as Clostridium and Escherichia coli.⁹ 
More beneficial bacteria, fewer potentially harmful bacteria: kimchi may just be a tasty ally of your gut microbiota . 

Caution: effects… and dosage matter!

Given this promising nutritional profile, some researchers have explored the potential links between kimchi consumption and a surprisingly wide range of health outcomes, from obesity, cancer, atopic dermatitis, irritable bowel syndrome, and even cardiovascular health and skin health … ^{3,6,7,10–14}
A few studies have been conducted, but they remain scarce and are often limited to Asian populations. In short, a little caution is warranted when interpreting the results, which remain inconclusive, and even when an effect is observed, it tends to be fairly modest.

For example, with regard to obesity, some studies suggest that kimchi consumption may be associated with a potential beneficial effect. One large study that followed 115,726 Koreans found that moderate kimchi consumption—1 to 3 servings per day (perfectly common in Korea, perhaps a little ambitious for the average Westerner)—was associated with a lower prevalence of obesity, particularly among men. But caution: this does not mean there is a cause-and-effect relationship. Kimchi lovers may simply be Koreans who tend to lead healthier lifestyles overall.¹
Nevertheless, another study—this time involving 3 grams of powdered kimchi daily (versus a placebo)—seems to support a potential role for kimchi in weight management.¹⁵ Let’s also put this “discovery” into perspective: eating more vegetables has been linked to better weight management for quite some time… 
Of course, as with most things in nutrition, more is not necessarily better: beyond a certain level of consumption, any potential benefits may diminish, because kimchi, due to its recipe, contains a lot of salt, which can contribute to high blood pressure and is a risk factor for stomach cancer.^1,2,16