Revisiting the potential anti-obesity effects of kimchi and lactic acid bacteria isolated from kimchi: a lustrum of evidence

Abstract

Kimchi, a renowned and culturally significant Korean dish, has gained global recognition as a superfood due to its abundant nutritional content and positive impact on human health. The process of producing kimchi involves the fermentation of various vegetables using lactic acid bacteria (LAB). The primary genera of kimchi LAB encompass Lactobacillus, Lactococcus, Leuconostoc, Pediococcus, and Weissella. Impressively, kimchi comes in over 200 varieties with cruciferous vegetables as its main ingredients, complemented by a range of secondary ingredients that contribute to its nutritional and holistic health benefits. These secondary ingredients include salted fish, ginger, garlic, and red pepper powder. Due to its various functional properties, kimchi has attracted considerable interest. Kimchi has been extensively studied, and its recognized health benefits, including anti-oxidant, anti-tumor, anti-inflammatory, anti-microbial, anti-obesity, hepatoprotective, neuroprotection, anti-allergic, regulation of immunological responses, and many more, have been covered in many review papers. A current literature review regarding the anti-obesity properties of kimchi and kimchi LAB is currently lacking. Therefore, the present review has directed its attention towards the literature concerning the anti-obesity properties of kimchi and LAB derived from kimchi over the last five years.

Introduction

Obesity is a notable public health concern, and its prevalence has been consistently increasing in recent decades [1]. The primary cause of obesity is an imbalance in the body's energy homeostasis, which results in abnormal fat buildup, chronic inflammation, and insulin resistance [2]. Recent research has established a strong correlation between dysbiosis in the gut microbiota and obesity [3]. Factors such as economic development, a sedentary lifestyle, genetic, epigenetic, and environmental factors contribute significantly to the substantial increase in obesity [4]. It is recognised as a risk factor for several metabolic disorders, such as hyperlipidemia, type 2 diabetes, non-alcoholic fatty liver disease, and cardiovascular diseases [5]. Therefore, it is important to manage and prevent obesity in order to avoid the consequences associated with it. In pursuit of better intervention strategies, the effects of various ethnic foods, such as kimchi, and lactic acid bacteria (LAB) and their metabolic products against obesity have garnered significant attention from the scientific community.

Kimchi is a traditional and well-enjoyed Korean dish made by fermenting vegetables [6, 7]. The dish primarily consists of a variety of green vegetables, mainly radish and Chinese cabbage, with additional spices incorporated as supplementary elements [8]. Kimchi is widely recognised for its health benefits due to the presence of healthy vitamins, minerals, antioxidants (vitamin C, carotenoids, flavonoids, and other phenolic constituents), and various LAB strains [9, 10]. The American Journal of Public Health identified kimchi, along with Greek yoghurt, Spanish olive oil, Indian lentils, and Japanese bean products, as one of the healthiest foods in the world in 2006 [11]. Over 200 varieties of kimchi have been documented based on the type of ingredients, and regional and seasonal variations [10, 12]. Kimjang is the practice of a characteristic food culture for producing a large quantity of kimchi specifically for consumption during the winter season, an essential tradition for Koreans [13]. Korea has devised an exclusive technique for storing and conserving kimchi [8]. The UNESCO-established Lists of Intangible Cultural Heritage [13] included a description of this Kimjang culture in 2013. Kimchi, a significant player in the Korean ethnic food industry (K-food), is acknowledged as a healthy food in the United States [14].

The most commonly consumed types of kimchi include cabbage kimchi, radish kimchi, and young radish kimchi [15]. According to a survey carried out by the Ministry of Agriculture, Food, and Rural Affairs (MAFRA) of Korea in 2020, it was found that 1.78 million tons of kimchi were consumed by Koreans, with a major share contributed by cabbage kimchi [15]. Based on MAFRA’s data, the value of kimchi sales abroad increased to US$74.7 million, representing a 44.3% growth compared to the previous year [16].

Kimchi is bestowed with many health-promoting properties, including antioxidant [17, 18], anti-inflammatory [18], anticancer [19, 20], hepatoprotective [21, 22], neuroprotective [23], and antimicrobial [24]. Extensive research has been conducted to enhance the functioning of kimchi. Specifically, fermenting methods, LAB, kimchi components, and metabolites have all been found to influence its functionality [25]. More recently, Choi et al. [26] discovered that the microbial and metabolic profiles of radish kimchi varied based on the size of the raw materials. Radish's small size resulted in faster LAB growth as well as variations in metabolite production [26].

Kimchi not only provides a harmonious nutritional composition, but it is also abundant in LAB, which plays a crucial role in the fermentation of kimchi and the intricate development of its flavors [27]. The LAB microorganisms generate beneficial substances such as organic acids, oligosaccharides, γ-aminobutyric acid, ornithine, conjugated linoleic acids, and mannitol. These chemicals play a role in enhancing flavor and promoting functionality [28]. The primary LAB genera found in kimchi are Leuconostoc (Leu.), Pediococcus (P.), Lactobacillus (Lb.), and Weissella (W.), regardless of the type of kimchi [28]. According to a recent review, Cha et al. [15] discovered that the most common types of LAB genera found in cabbage kimchi are Leuconostoc, Lactobacillus, and Weissella. On the other hand, Lactobacillus and Weissella have been found to be the most common types of genera in radish and young radish kimchi, respectively. Despite their mutual prevalence in kimchi, the relative abundance of LAB depends on the main ingredients [15]. Furthermore, the production of organic acids by LAB during kimchi fermentation causes a change in the pH of the fermentation medium, which modulates the microbial population [29]. Some of these LABs are commonly referred to as probiotics, and the isolation and efficacy of kimchi-derived LAB have been duly recognized.

Previously, we published an overview of kimchi and kimchi-derived LAB and their health benefits. The study meticulously reported the beneficial effects of kimchi and the LAB derived from it against oxidative stress, cancer, dyslipidemia, hypertension, inflammation, immunity, etc. Additional studies included effects of kimchi on clinical trials assessing its effects on diverse issues, including obesity, gut microbiota, and metabolic parameters [30]. More recently, a scoping review article on the effects of kimchi intake on human health based on randomized controlled trials (RCTs) has been documented. Despite the low number of included clinical studies, the authors support the idea that kimchi supplementation may be a safe and beneficial treatment alternative for managing general well-being, obesity, and irritable bowel syndrome. They suggested that further investigations should be conducted in the near future [31]. Moreover, a review article focusing on the anti-obesity effects of kimchi and kimchi-derived LAB is lacking. Given the importance, this review paper aimed to present current data on the anti-obesity benefits of kimchi and LAB derived from kimchi over the last five years. The review paper includes information on both experimental and clinical findings.

Search strategy and inclusion criteria

A thorough literature review was performed using many academic databases, including Google Scholar, Science Direct, PubMed, and Embase, to locate appropriate research papers published between January 2019 and December 2023. We searched using many keywords, including "kimchi," "lactic acid bacteria," "obesity," "anti-obesity," "antiadipogenic effects," "kimchi and obesity," "lactic acid bacteria and obesity," "lactic acid bacteria from kimchi," and "kimchi and gut microbiome," to find papers that were easy to read about how kimchi and LAB from kimchi can help fight obesity. The objective was to present readers with up-to-date advancements about the anti-obesity properties of kimchi and its derived LAB, as well as their underlying mechanisms of action. A detailed search was performed to include clinical studies in addition to the experimental findings. The review also selected studies published in Korean but with abstracts written in English.

Kimchi and potential anti-obesity effects

This section describes the anti-obesity effects of Kimchi published over the last five years. It was observed that there are many studies documenting the anti-obesity effects of LAB-derived from kimchi. However, the anti-obesity effects of kimchi or kimchi enriched with some other functional products are sparsely reported.

Given the importance of kimchi, many functional studies of this ethnic food have been documented [9, 32]. Moreover, continuous efforts are being made to develop functional kimchi to enhance the health benefits of kimchi. On this line, a study found that kimchi mixed with 7% citrus concentrate from Jeju Island could help fight obesity by stopping the fat buildup and restraining the rise in fat levels in 3T3-L1 adipocytes (Table 1). Notably, the extract-enriched kimchi showed higher levels of total phenolic content and total flavonoid content compared to normal kimchi. A higher antioxidant activity was also observed for enriched kimchi compared to normal kimchi (Table 1) [33]. In a follow-up study, the authors evaluated the anti-obesity effects of extract-enriched kimchi in vivo. The supplementations reduced the gain in body weight and white adipose tissue weight significantly. Further, the treatment also showed anti-diabetes effects, as evidenced by lowered insulin, glucose, and homeostasis model assessment-estimated insulin resistance levels. Despite the high glucose content of kimchi, the anti-obesity effects of kimchi could be attributed to the presence of LAB and auxiliary ingredients such as red chili powder and garlic. The authors advocated that future research should focus on the synergistic and beneficial effects, along with the mechanistic implications of citrus extract-enriched kimchi [34]. A further intriguing continuation study demonstrated the anti-obesity effects of kimchi with red yeast rice (0.08% of red yeast rice) extract in 3T3-L1 adipocytes by demonstrating effects on intracellular triglycerides (TG) levels and gene expressions related to obesity, as well as effects in mice on body weight, serum and hepatic lipid content, and gene expression (Table 1). Better antioxidant capacity was reported for kimchi with red yeast rice compared to normal kimchi, this could be due to both kimchi and red yeast rice being proven to have antioxidant potential. The study also determined high levels of Monacolin K in red yeast rice [35].

Table 1 Anti-obesity effects of kimchi based on experimental studies

More recently, catechin functional kimchi (CFK) was evaluated for anti-obesity effects in high-fat diet (HFD)-fed mice. Compared to other kimchi’s: commercial kimchi, standard kimchi, and green tea functional kimchi, used in the study, CFK downregulated expressions of genes related to adipogenesis and lipogenesis and lowered inflammatory-related genes, while lipolysis-related gene expression was upregulated (Table 1). The authors also elucidated 39 active compounds from CFK, which have been proven to have many health benefits [36]. These studies suggest that the better anti-obesity and other health effects of enriched kimchi compared to normal kimchi could be due to higher antioxidant potential and improved bioactive constituents compared to normal kimchi. Future studies should be evaluated with different types of kimchi and for other functional attributes.

A recent study selected four LABs, including Lb. (reclassified as Levilactobacillus) brevis JC7, Leu. mesenteroides KCKM0828, Companilactobacillus allii WiKim39, and Lactococcus lactis WiKim0124 with potential anti-obesity potential, used them as starter cultures for preparing kimchi and compared them with normally fermented kimchi to demonstrate health benefits, especially against obesity, in 3T3-L1 cells. All four strains were used at 10⁷ colony forming units (CFU)/mL based on viability analysis and demonstrated significantly lowered TG levels and lipid accumulation with JC7 and KCKM0828 being the strongest inhibitors. Starter kimchi: SK1 (JC7), SK2 (KCKM0828), SK3 (WiKim39), and SK4 (WiKim0124) treatments affected the lipid profile, accumulation, and expression of genes associated with obesity [37] (Table 1). The study suggests that the health functionality of kimchi could be enhanced by the selection of appropriate strains. However, the effects have only been demonstrated using cell lines. More studies, including animal models, should be conducted in future.

LAB-derived from Kimchi and anti-obesity effects

Imbalance in the gut microbiota, characterised by decreased diversity, abundance, and richness, contributes to the development of several chronic ailments such as obesity, inflammatory disorders, gastrointestinal diseases, metabolic syndrome, cancer, and brain diseases [38, 39]. Many studies on obese animal and human subjects have documented a higher Firmicutes/Bacteroidetes ratio compared to the normal control. However, contradictory findings have also been published, considering this a hallmark of obesity [40]. Further, imbalance in Firmicutes and Bacteroidetes can result in a condition known as leaky gut, which in turn contributes to the development of inflammatory diseases and other systemic diseases [41]. Although the composition of healthy gut microbiota can vary depending on the geographical region [42]. However, altered gut microbiota diversity has been observed in obesity. Table 2 describes the cumulative information on LAB-derived from kimchi and its anti-obesity effects. The detailed information pertaining to doses and biological effects in different cell and animal models has been narrated in the supplementary Table S1.

Table 2 LAB derived kimchi and their anti-obesity effects based on experimental studies

The dysbiosis of the gut microbiota can be regulated by various strains of LAB. Kimchi-derived probiotic strains and their metabolites exert positive impact on metabolism by modulating the gut microbiome and obesity-related markers. For example, Lb. (reclassified as Lactiplantibacillus) plantarum (TCI378) proved to have potential probiotic properties, and its cell free supernatant (CFS) was documented to have cholesterol-lowering and fat-reducing potential. TCI378 cells lowered cholesterol by 48% compared to the control and showed their bile salt hydrolysate activity. Both dead TCI378 cells (unpublished, by 9%) and TCI378 cells’ metabolites reduced (14% reduction) oil red O staining, and TCI378 cells’ metabolites reduced expressions of adipocyte-specific genes (Table 2) (Supplementary Table S1) [43]. The study indicates that both probiotic bacteria and their metabolites exhibit anti-obesity properties. Many experimental and clinical studies have documented the anti-obesity potential of postbiotics [44]. Future research should assess the postbiotic capabilities of kimchi-derived LAB as potential anti-obesity agents.

Administration of Lb. plantarum LMT1-48 (10⁹ CFU/day) in Enterobacter (E.) cloacae-induced obese (HFD-fed) mice led to body fat loss and reduced abdominal fat volume. Additionally, serum levels of leptin and total cholesterol were also significantly reduced. Cell-free supernatants of LMT1-48 showed antimicrobial activity against E. cloacae, a pathogenic strain of the colon. The mechanism by which LAB generated from kimchi acts against obesity is not solely dependent on the Firmicutes/Bacteroidetes ratio but may also involve other bacterial phyla, such as Proteobacteria and Verrucomicrobia. For example, the LMT1-48 administration also modulated gut microbiota diversity and levelled up phylums Proteobacteria and Verrucomicrobia by 2.75% and 1.62%, respectively. In the Verrucomicrobia phylum, the Akkermansia genus is the most represented and known to have reduced dominance in obese mice. Thus, the authors advocate that LMT1-48 may have anti-obesity effects through gut microbiota modification. They suggest genus-level identification for future studies [45] (Table 2) (Supplementary Table S1). Lactobacillus plantarum LB818 from another study was shown to have anti-obesity effects along with modulating the gut microbiota. LB818 treatment led to a significant reduction in total body weight, liver weight, intestinal fat weight, and total fat weight compared to HFD-fed mice. LB818 supplementation altered serum biochemical markers along with significantly reduced fasting blood glucose levels (Table 2) (Supplementary Table S1). Additionally, animals group fed with HFD and LB818 reported increased levels of Bacteroidetes, Akkermanasia, Lactobacillus, and Bifidobacteria species. The Bacteroidetes/Firmicutes ratio was found to be higher, while Firmicutes levels were significantly decreased in the mouse group supplemented with LB818 [46] (Table 2) (Supplementary Table S1).

Another strain, Lb. plantarum K50, modulated gut dysbiosis in HFD mice by lowering the Firmicutes/Bacteroidetes ratio, modulating the gut microbiota (increased alpha and beta diversity), and elevating the short-chain fatty acid (SCFA) levels compared to HFD-fed control. A significantly reduced levels of Actinobacteria and Erysipelotrichia (more prevalent in obese individuals) and an increased level of Lactobacillus were observed. Oral administration of K50 ameliorated obesity by reducing fat accumulation, adipocyte generation, and chronic low-grade inflammation [47] (Table 2) (Supplementary Table S1). These studies indicate that gut microbiota dysbiosis is also an indicative factor when considering obesity-related markers [46]. Our research group also documented the anti-obesity effects of Lb. plantarum ATG-K2 against in vitro and in vivo models. These effects are believed to be influenced by the modulation of the gut microbiota and its metabolites. The ATG-K2 supplementation increased the abundance of Lactobacillaceae family, SCFAs and branched SCFAs in feces [48] (Table 2) (Supplementary Table S1). These above-discussed studies show that the modulation of gut microbiota through supplementation with different probiotic bacteria may help in attenuating obesity and other disorders.

Choi et al. [49] studied how Lb. plantarum LMT1-48 can help fight obesity in 3T3-L1 adipocytes and HFD-fed obese mice. Lb. plantarum LMT1-48 treatment downregulated expressions of lipogenic genes in both cell and animal models and at least 10⁶ CFU of LAB significantly lowered body weight and abdominal fat volume in treated animals [49]. Another study documented the antiadipogenic effects of Lb. plantarum KU15117 by downregulating expressions of genes associated with early adipocyte differentiation and lowering lipid accumulation in vitro [50]. A study published in Korean documented the probiotic characteristics and lipid-lowering effects of different LAB strains (OS-15, 48, 102, and 120). The strain OS-15 showcased the strongest effects and the strain was identified as Lactiplantibacillus plantarum based on 16S rRNA sequencing (Table 2) (Supplementary Table S1) [51].

Now a days research on the beneficial effects of postbiotics and paraprobiotics has garnered significant attention, including for anti-obesity effects [52]. Among recent studies, Lee et al. (in Korean) [53] compared the anti-obesity effects of live Lb. plantarum (pF1 and PNU) and dead Lb. plantarum (nF1) in HFD-fed rodents. The dead nF1 plantarum outperformed pF1 and PNU in terms of lowering body, epididymal, and liver fats, as well as ameliorating serum markers and expressions of lipid metabolism-related genes (Table 2) (Supplementary Table S1) [53]. Besides evaluating effects on body weight gain and other lipid metabolism markers, studies on LAB modulating obesity-related signaling pathways are also important and have gained significant momentum. Heat-killed Lb. plantarum K8 showed anti-obesity effects in both cell and animal models in one such study. Notably, 1 × 10⁹ CFU/mL of dead K8 showed greater anti-obesity effects compared to live K8 at the same concentration, whereas live K8 showed cytotoxicity. In animals, both live and heat-killed treatments showed weight reduction and blood TG reduction after 12 weeks’ supplementation. The greater anti-obesity effects of heat-killed strain were due to the enhanced expressions of suppressor of cytokine signaling (negative regulator) and some other potential regulators that blocked the activation of Janus tyrosine kinase 2 and signal transducer and activator of the transcription 3 pathway, and inhibited the lysogenic enzyme-mediated fat synthesis in adipocytes [54] (Table 2) (Supplementary Table S1). The study advocates that the paraprobiotics are advantageous in terms of lower toxicity, stability, and ease of distribution than live probiotics. Future research should focus on both live and dead probiotics, as well as their postbiotic components from strains with already reported anti-obesity properties.

Three kinds of Lb. (reclassified as Latilactobacillus) sakei (CJLS03, CJB38, and CJB46) strains were tested on a HFD-fed animal model to see how well they worked at fighting obesity. Among all, the strongest and dose-dependent body weight-reducing effect was observed with strain CJLS03, isolated from Kimchi. The other two strains (CJB38 and CJB46) were isolated from human faecal samples. Overall, a high dose of the kimchi-derived strain gave the most favourable outcome pertaining to a significant reduction of obesity-related markers (Table 2) (Supplementary Table S1). The study suggests the importance of strain and dose selection for the clinical applications [55]. Later, Yosep et al. evaluated the effects of CJLS03 on obesity-related genes, microbiota modulation, and SCFAs levels both in serum and feces. CJLS03 supplementation demonstrated a shift in microbiological diversity from PC1 to PC3. At the family level, a strong increase in the Rikenellaceae, the Clostridiaceae, Sphingomomonadaceae, and Oxalobacteraceae families and a strong reduction in the Bacteroidales Family S24-7 compared to the HFD control group was observed. Compared to HFD, no effect was observed for Bifidobacterium spp. (Actinobacteria) or Clostridium IV and XIVa (Firmicutes). Of note, CJLS03 administration enhanced Lactobacillus population by more than 15 fold [56] (Table 2) (Supplementary Table S1).

Won et al. [57] documented better anti-obesity effects of the Lb. sakei ADM14 strain than Lb. plantarum and Leu. pseudomesenteroides while evaluating the anti-adipogenic effects of 225 LAB strains isolated from 11 different types of kimchi. The ADM14 strain showed significantly lowered TG levels and downregulated expressions of various adipogenic markers (Table 2) (Supplementary Table S1). Kimchi-derived ADM14 strain has potential probiotic properties and showed an anti-adipogenic effect in 3T3-L1 adipocytes [57]. The authors also evaluated anti-obesity effects of ADM14 in HFD-fed mice. ADM14 supplemented group had a significantly lower (by 25.8%) body weight compared to HFD group. Additionally, ADM14 supplementation improved energy harvesting, restored Firmicutes to Bacteroidetes ratio, and increased abundance of specific taxa such as such as Alistipes and Bacteroides faecichinchillae. At the phylum level, a significant higher ratio of Bacteroidetes and Deferribacteres and lower ratio for Verrucomicrobia was observed compared to HFD. At the class level, Bacteroidia, Deferribacteres_c, and Clostridia were upregulated, while Erysipelotrichia and Epsilonproteobacteria were downregulated. Further, at the family level, significant increase was observed for Muribaculaceae, Bacteroidaceae, and Lachnospiraceae [58]. Despite a member of Firmicutes, increase in Lachnospiraceae was shown to be observed with anti-obesity effect, as published earlier with a strain of Lb. plantarum [59] (Table 2) (Supplementary Table S1). These studies indicate the importance of Lb. sakei ADM14 as a therapeutic probiotic functional food with anti-obesity potential. More in-depth studies are required to have comprehensive information about Lb. sakei on modulating gut microbiota in relation to obesity.

Beside gut microbiota dysbiosis, malfunctioning gut barrier function can lead to the intestinal inflammation due to infiltration of inflammatory molecules, resulting in obesity. Intestinal epithelial cells play an essential function in maintaining gut homeostasis [60]. Physical barriers called cell junctions such as the tight junction (TJ) and adherence junction, firmly connect epithelial cells. The junction consists of occludin, claudin, other proteins, as well as intracellular proteins (plaque), including cingulin and zonula occludens (ZO) [61] (Table 2) (Supplementary Table S1). Studies have been documented on the effects of kimchi-derived LAB on gut barrier function and on carbohydrate absorption by epithelial cells. For example, Lb. sakei WIKIM31 enhanced the expression of TJ proteins, including claudin-2, occludin, claudin-5, and ZO-1. The supplementation of WIKIM31 led to anti-obesity effects by modulating gene expressions associated with lipid metabolism and suppressing inflammatory markers in an HFD-fed animal model (Table 2) (Supplementary Table S1) [62]. Park et al. [63] evaluated the anti-obesity potential of Lb. plantarum MGEL20154 in HFD-fed mice. The oral intake of MGEL20154 reduced weight gain and epididymal fat size along with decreased food efficacy. The cell surface hydrophobicity was found to be positively related to adhesion to human epithelial (Caco-2) cells treated with MGEL20154. The probiotic treatment modulated the immune response by restoring intestinal barrier integrity through downregulation of nuclear factor kappa-light-chain-enhancer of activated B cells and upregulation of mitogen-activated protein kinase/extracellular signal-regulated kinase expressions in epithelial cells. The carbohydrate absorption of the intestinal cells was also decreased with MGEL20154 treatment, as evidenced by modulated gene expression [63] (Table 2) (Supplementary Table S1).

Despite many species of the genus Lactobacillus, the anti-obesity effects of other important kimchi-derived LAB species have also been documented. For example, a Korean study showed the anti-obesity effects of W. confusa WIKIM51 in diet-induced obese mice. The strain WIKIM51 reduced the expression of adipogenesis-related genes in cells and inhibited body weight gains in animals while also modulating the microbial communities, especially significantly lowering the Firmicutes to Bateroidetes ratio [64]. In another study, Lb. (reclassified as Levilactobacillus) brevis OPK-3 documented its anti-obesity effects in vitro and in vivo. The OPK-3 lowered lipid accumulation in the cell line and significantly lowered body weight, epididymal fat tissue mass, and reduced serum and hepatic markers in HFD-fed mice supplemented with OPK-3 (Table 2) (Supplementary Table S1). The treatment also downregulated mRNA levels of inflammatory markers and modulated microarray analysis of hepatic gene expression profiles, suggesting beneficial effects against weight gain and inflammation [65]. Lee et al. [66] evaluated the anti-obesity and safety aspects of Lb. (reclassified as Lacticaseibacillus) paracasei AO356 in HFD-fed obese mice. Following treatment, plasma lipid levels were significantly ameliorated. Regarding safety, standard assessments such as antibiotic resistance, hemolytic, and enzymatic assays were conducted to evaluate AO356. The strain performed favorably in these tests. The study found AO356 as a healthy functional food that could be used for the treatment of obesity [66] (Table 2) (Supplementary Table S1).

Most of the studies have evaluated the effects of a single probiotic strain as anti-obesity agents and gut modulators. Of note, a study by Park et al. [67] evaluated the effect of the microbial community from kimchi on obesity in an HFD-fed mouse model. The anti-obesity effects of the microbial community were due to the modulation of the gut microbiota. The microbial community supplementation resulted in decreased body weight, adipose tissue, and liver weight gains. Concerning gut microbiota, the relative content of Muribaculaceae was higher, whereas the relative contents of Akkermansiaceae, Erysipelotrichaceae, and Coriobacteriaceae were observed to be lower in the animal group treated with the microbial community compared to the control. Microbial community treatment also influenced energy metabolism, as serum levels of stearic acid, arachidic acid, and fumaric acid were decreased in the animal group treated with kimchi microbial community [67] (Table 2) (Supplementary Table S1).

Kim et al. [68] evaluated the anti-obesity effects of three Lb. fermentum SMFM2017-NK4, NK3, and NK2 strains, as well as P. pentosaceus SMFM2017-GK1 in a HFD-fed animal model. The study evaluated expressions of lipid-metabolism-related genes, antioxidant enzymes, and serum biomarkers. Among all, the inhibition percentage for 3T3-L1 cell differentiation was found to be higher for NK4 (21.44%), followed by NK3 (20.99%), GK1 (20.45%), and NK2 (15.57%). In animal experiments, all selected strains showed significant weight reduction, though better results were obtained for Lb. fermentum SMFM2017-NK4 for the above-said biomarkers and obesity-related genes (Table 2) (Supplementary Table S1). Thus, the study suggests the potential role of NK4 in preventing obesity by inhibiting fat accumulation [68].

Clinical studies

Clinical  studies showing the effects of probiotics against obesity are limited in number. However, a few recent studies involving three randomized, double-blind, placebo-controlled (RCT) studies based on LAB-derived from kimchi and one epidemiological study based on kimchi intake have been documented. For example, the anti-obesity potential of Lb. sakei CJLS03 was evaluated in a RCT study. The study evaluated 114 individuals with a BMI ≥ 25 kg/m², however, 95 individuals completed the study. The subjects were given two doses of 5 × 10⁹ CFU of Lb. sakei daily for 12 weeks. Compared to the placebo group (0.6 kg increase), body fat mass decreased (by 0.2 kg) in the treatment group, with a significant difference between groups (P = 0.018). The treatment group exhibited a waist circumference reduction of 0.8 cm compared to the placebo group. No change was reported for body weight or BMI. The study reported mild adverse effects with no significant change, though reducing trends were observed in the treatment group [69]. The effect of Lb. sakei OK67 (DW2010) was documented in another RCT study involving a total of 100 overweight individuals (lifestyle-modified) with BMI ≥ 25 kg/m² and < 30 kg/m². The individuals were supplemented with 1.0 × 10¹⁰ CFU (2.0 g/day) or placebo for 12 weeks. The visceral fat area was significantly decreased compared to placebo. No significant differences were observed either in body fat change or biochemical parameters, between groups. The study reported no adverse effects [70]. One more RCT study evaluated the effect of Lb. plantarum K50 on 81 individuals with a BMI ≥ 25 kg/m². The individuals received two doses of 2 × 10⁹ CFU or placebo for a period of 12 weeks. No significant changes were observed for body weight, fat mass, or abdominal fat area. Further, K50 supplementation reduced total cholesterol and TG levels as well as significantly modulated the gut microbiota. Compared to the placebo, the relative abundance of the phylum Actinobacteria was decreased, while the relative abundance of Lb. plantarum was significantly increased. No serious adverse effects were reported [71].

A new epidemiological study from Korea examined the correlation between kimchi consumption and weight loss using data from the Health Examinee cohort study. The correlation analysis involved a total of 58,290 participants, while the risk assessment specifically focused on 20,066 people with a BMI of ≥ 25 kg/m². The study employed a semi-quantitative food frequency questionnaire to collect data on the consumption of kimchi and specifically focused on four distinct types of kimchi for the analysis. The correlation study revealed a significant inverse relationship between kimchi consumption and the increase in BMI range in both men (β 0.169, 95% CI (0.025, 0.313)) and women (β 0.140, 95% CI (0.046, 0.236)). Observations in risk assessment indicate that consuming a moderate amount of kimchi (about 2–3 servings per day) is linked to the maintenance of a healthy weight in men. The study revealed a significant (P < 0.05) association between cabbage (Baechu) kimchi consumption and men. In summary, the study indicates that consuming a moderate amount of kimchi over an extended period of time was linked to weight reduction in middle-aged and older individuals from Korea, specifically among men. Obese Koreans who consumed a moderate amount of kimchi over a lengthy period of time were more likely to reach a normal weight [72].

Conclusions

Kimchi is a well-liked Korean food that is known for its rich nutritional content and high intake of LAB. The fermentation of kimchi by LAB not only enhances its flavor and extends its shelf-life, but also yields numerous health-promoting benefits. Studies have shown that both kimchi and LAB derived from kimchi have demonstrated anti-obesity effects in both animals and humans. These effects are attributed to the modulation of the lipid metabolism and multiple enzymes in the liver and adipose tissues, as well as various serum biomarkers. Additionally, it activates numerous signalling pathways and improves the low-grade chronic inflammatory state. Increasing the presence of Akkermansia, Lactobacillus, and Bifidobacterium in the gut microbiota, as well as maintaining a balanced ratio of Bacteroidetes to Firmicutes and promoting the production of SCFAs and the repair of the leaky gut are additional processes that contribute to the anti-obesity benefits. Future research should focus on evaluating the effects on other phylums and genera present in the gut.

The effects of Kimchi LAB and metabolites (CFS) are dose-dependent and strain-specific. Further, the utilization of a microbial community formed from kimchi provides health and safety benefits. Nevertheless, it is undeniable that there are variations from one batch to another. Therefore, further research is required to confirm the impact of the microbial population obtained from kimchi, fermented for varying durations of time, on obesity. Moreover, postbiotics and paraprobiotics from LAB should be evaluated as potential anti-obesity agents. Utilizing a pure starter culture for fermenting kimchi and evaluating kimchi in conjunction with other bioactive substances, resulted in enhanced antioxidant and anti-obesity properties, as well as a greater polyphenolic composition. Therefore, future research should prioritize the examination of strain-specific starter culture-based kimchi in order to assess its anti-obesity properties. Several randomised and one epidemiological study have been documented. However, the effectiveness of many probiotics is still restricted due to inadequate adhesion and colonization, prompting ongoing research to address this issue. In summary, both kimchi and kimchi-derived LAB documented anti-obesity effects. It is important to conduct research based on clinical studies for the management and prevention of obesity.