Kimchi Powder on Gut Health

BACKGROUND AND RATIONALE

Kimchi, a traditional Korean fermented vegetable food, has been reported to possess a range of health-related functionalities including antioxidant, anti-aging, anti-obesity, and anti-cancer activities, and more recently, effects on cognitive function. These functionalities are attributed to the bioactive compounds, lactic acid bacteria, and fermentation metabolites present in kimchi.

Most recent research on the functionality of kimchi has focused on lactic acid bacteria isolated from kimchi rather than on kimchi itself. Although research on isolated strains is valuable, kimchi is a compositionally complex food manufactured from multiple ingredients, and its functionality as a whole food requires verification in cell and animal models followed by human studies. Among the health outcomes of interest, improvement of gut health warrants scientific verification, together with subsequent analysis of its relationship to related functions such as immune function.

The gut microbiome refers to the totality of microorganisms present in a given environment together with their genetic information. Microbial composition differs by body site and confers site-specific characteristics. The intestine harbors the largest and most diverse microbial population in the human body, and this population has been reported to exert substantial influence on health and on a wide range of diseases. As the association between the microbiome and health has become better established, research aimed at maintaining health and preventing disease through modulation of the microbiome has expanded. Substances secreted by intestinal microorganisms act on host cells and mediate diverse functions, making the study of host-microbe interactions and the regulation of cellular function an important area of investigation.

Evidence regarding changes in the human microbiome following kimchi consumption remains limited. Accordingly, this study performs human microbiome analysis in parallel with clinical assessment in order to examine the relationship between kimchi intake and improvement of gut health, to identify key intestinal microorganisms involved, and thereby to verify the health functionality of kimchi.

The daily intake for this study was derived from preclinical data. In a study using C57BL/6 male mice, daily administration of the test material at 600 mg/kg for 6 weeks produced no notable toxicity and was associated with improvement in gut health parameters. Allometric conversion to a human equivalent dose for a 60 kg adult (600 mg/kg x 60 kg x 0.08) yielded approximately 2,880 mg/day. Taking manufacturing and economic feasibility into account, the intake of kimchi powder was set at 3,000 mg/day.

OBJECTIVES

The overall objective is to scientifically and clinically evaluate whether oral intake of kimchi powder as a food ingredient is safe and whether it is effective in improving gut health.

Primary objective: To evaluate the change in the total score of the IBS Severity Scoring System (IBS-SSS) in the test group compared with the control group following intake of the study food.

Secondary objectives: To evaluate, in the test group compared with the control group following intake of the study food, the changes in (1) stool form as assessed by the Bristol Stool Form Scale; (2) the Irritable Bowel Syndrome Quality of Life (IBS-QOL) questionnaire score; (3) the Visual Analogue Scale for Irritable Bowel Syndrome (VAS-IBS) score for bowel symptoms; (4) defecation symptom assessment (diarrhea frequency); (5) serum IL-1beta concentration; (6) serum TNF-alpha concentration; (7) serum IgG concentration; (8) serum IgA concentration; (9) serum hs-CRP concentration; and (10) fecal calprotectin.

STUDY DESIGN

This is a single-center, randomized, double-blind, placebo-controlled, parallel-group human study conducted at Pusan National University Yangsan Hospital, Republic of Korea. The study is sponsored by the World Institute of Kimchi, an affiliated institute of the Korea Food Research Institute, and is conducted with the support of a contract research organization.

Volunteers who provide written informed consent of their own free will are assessed against the inclusion and exclusion criteria. Participants already taking health functional foods or medications judged not to affect the study may continue their use concomitantly. Eligible participants are randomly allocated to the test group or the control group in a 1:1 ratio. Randomized participants receive the study food together with an intake diary and consume the product three times daily according to the instructions provided. Total participation is approximately 10 weeks, comprising a screening period of up to 2 weeks and an 8-week intake period.

SAMPLE SIZE

A total of 70 participants (35 per group) will be enrolled. The number of participants required for efficacy evaluation is 28 per group (56 in total), and a dropout rate of 20% was applied to determine the enrollment target.

This study is designed as a preliminary (pilot) study intended to increase the likelihood of success of a subsequent confirmatory human study. Its purposes include establishing the basis for sample size calculation, determining an appropriate intake level, estimating effect size, exploring efficacy endpoints, identifying adverse reactions, and identifying operational issues anticipated during the conduct of a human study. Recruitment size was determined with reference to published recommendations for pilot trials (Teare et al.; Sim and Lewis), which indicate that a scale of 50 to 70 participants is appropriate for a pilot study. A formal power calculation was therefore not performed.

RANDOMIZATION AND BLINDING

Finally enrolled participants are allocated 1:1 to the test group or the control group using block randomization. Block size is determined arbitrarily or randomly by the study statistician and is not disclosed, so that the block size and the number of blocks cannot be inferred. The total number of randomization entries generated corresponds to approximately 120% of the target enrollment. A three-digit identification code (randomization number) is assigned to participants in order of enrollment, and packaged test or control food is dispensed according to that code. Once a randomization number has been assigned, it is not reused even if the participant discontinues.

The randomization list is generated by the monitor or a third party and provided to the sponsor. The sponsor seals each participant's allocation in an individual opaque envelope and supplies these to the principal investigator for storage and management.

To maintain double blinding, the test food and the control food are produced as capsules identical in external appearance and are supplied in identical packaging. The allocation of participant codes is kept sealed by the principal investigator and is not disclosed until the end of the study. If unblinding becomes unavoidable due to the occurrence of a serious adverse reaction, only the allocation of the affected participant may be reviewed, as each allocation is managed in a separate sealed envelope. After completion of the study, the randomization codes are opened for efficacy analysis.

STUDY PRODUCTS AND ADMINISTRATION

Test food: kimchi powder, supplied in capsule form. Control food: placebo containing lactose and other excipients, in capsule form.

Both groups take a total of 3,600 mg/day (400 mg x 9 capsules), administered as 3 capsules three times daily after breakfast, lunch, and dinner with water. In the test group, this corresponds to 3,000 mg/day of kimchi powder. The intake period is 8 weeks (56 days).

Compliance is calculated from intake diaries completed by participants and collected at each visit. Concomitant treatments in place at the time of enrollment are recorded as concomitant therapy, and changes to concomitant therapy during the study period are avoided where possible. Concomitant medication use is minimized and permitted only where necessary for participant welfare and judged not to affect the study food, at the discretion of the principal investigator.

ELIGIBILITY

Inclusion criteria

(1) adults, male or female, aged 20 to 70 years; (2) body mass index of 25 kg/m2 or more and less than 30 kg/m2; (3) meeting the Rome IV criteria for diarrhea-predominant irritable bowel syndrome (IBS-D), defined as Bristol Stool Form Scale type 6 or 7 in 25% or more of bowel movements from 2 weeks before screening through the day of the screening visit; (4) absence of inflammatory bowel disease or malignancy; and (5) written agreement to refrain from consuming kimchi-containing foods for the duration of the study (approximately 2 months).

Key exclusion criteria include drug-induced constipation; constipation secondary to other conditions such as diabetes mellitus or thyroid disease; prior intra-abdominal surgery other than appendectomy; uncontrolled hypertension, diabetes mellitus, or thyroid dysfunction; hepatic or renal laboratory abnormalities exceeding predefined thresholds; severe cardiovascular or cerebrovascular disease or malignancy within the previous 6 months; severe psychiatric disorders or use of related psychotropic medication; severe alcohol use disorder; heavy smoking; hypersensitivity to the components of the study food; severe gastrointestinal symptoms; use of medications or foods that may affect the study results, including kimchi and probiotics; pregnancy, lactation, or planned pregnancy; and participation in another clinical trial within one month prior to screening.

STUDY SCHEDULE

The study consists of four visits.

Visit 1 (Day -14 to Day 0, screening): written informed consent; assessment of inclusion and exclusion criteria; collection of demographic information; medical history; physical examination; vital signs; measurement of efficacy endpoints; clinical laboratory tests; and review of prior medications. The Bristol Stool Form Scale is measured at screening and used as the baseline (Visit 2) value.

Visit 2 (Day 0, baseline): reassessment of inclusion and exclusion criteria; physical examination; clinical laboratory tests; dispensing of test or control food; measurement of efficacy endpoints; administration of questionnaires; and review of concomitant medications.

Visit 3 (Day 21 +/- 7): physical examination; dispensing of test or control food; measurement of efficacy endpoints; clinical laboratory tests; adverse event assessment; review of concomitant medications; and compliance assessment. IBS-QOL and fecal calprotectin are additionally measured at this visit.

Visit 4 (Day 56 +/- 7): update of demographic information (alcohol history, smoking history, body weight); physical examination; vital signs; clinical laboratory tests; measurement of efficacy endpoints; administration of questionnaires; adverse event assessment; review of concomitant medications; and compliance assessment.

EFFICACY ASSESSMENT

The primary time point for efficacy evaluation is Day 56 (Visit 4), analyzed as the change from baseline (Visit 2).

Primary efficacy endpoint: change in the IBS Severity Scoring System (IBS-SSS) total score.

Secondary efficacy endpoints: change in stool form (Bristol Stool Form Scale); change in IBS-QOL questionnaire score; change in VAS-IBS score; change in defecation symptom assessment (diarrhea frequency); and changes in serum IL-1beta, TNF-alpha, IgG, IgA, and hs-CRP concentrations and in fecal calprotectin.

Efficacy endpoints are measured at Visit 2 and Visit 4, except that the Bristol Stool Form Scale value obtained at screening serves as the Visit 2 value, and IBS-QOL and fecal calprotectin are additionally measured at Visit 3.

Dietary intake is assessed by the 24-hour recall method and physical activity by the International Physical Activity Questionnaire (IPAQ) at Visits 2 and 4, and pre- and post-intake values are compared in order to account for potential confounding.

EXPLORATORY ASSESSMENTS

Stool samples are collected at Visits 2, 3, and 4 for gut microbiome analysis, including balance indices, diversity indices, the ratio of beneficial to harmless bacteria, intestinal probiotic indices, and irritable bowel syndrome-related microbial indices.

To examine the effect of the study food on immune cell distribution, participants who provide separate written consent for the use of human biological material undergo collection of an additional 10 mL of blood at Visits 2, 3, and 4 for peripheral blood mononuclear cell (PBMC) isolation. Analyses include T cell subsets (CD4, CD8, Treg), cell activation markers (CD44, CD69), and cytokines, together with PBMC transcriptome analysis to assess changes in immune- and metabolism-related gene pathways. Samples are frozen and stored according to the institutional specimen handling standards of the study site and transferred to the sponsor for analysis under sealed dry ice conditions with procedures in place to prevent damage or degradation. Only the minimum information required for analysis is transferred, comprising the participant identification code, sampling time point, and group assignment. Residual specimens are stored for the retention period consented to by the participant and are subsequently disposed of in accordance with applicable procedures.

SAFETY ASSESSMENT

Safety is evaluated in all randomized participants. Safety endpoints comprise adverse events; abnormal findings on vital signs and physical examination or interview; and abnormal changes in hematology and blood chemistry values.

Adverse events are graded as mild (does not interfere with usual activities), moderate (interferes with usual activities and requires simple intervention), or severe (prevents usual activities and requires substantial intervention). Causal relationship to the study food is classified as definitely related, probably related, possibly related, probably not related, definitely not related, or unknown. All serious adverse events occurring during the study are reported to the sponsor within 24 hours of the investigator becoming aware of them, regardless of causality or of whether the study food was consumed, and are reported to the Institutional Review Board in accordance with its requirements.

STATISTICAL ANALYSIS

The per-protocol (PP) set is the primary analysis population for efficacy; the intention-to-treat (ITT) set is analyzed additionally and interpreted as supportive. The ITT set comprises all randomized participants regardless of study food intake. The PP set comprises participants within the ITT set who complete the study through Visit 4 without major protocol deviation. All statistical tests are conducted at a significance level of 5%. No interim analysis is planned.

Demographic variables measured at Visit 1 are summarized by group and compared between groups using the t-test (or Wilcoxon rank sum test) for continuous variables and the chi-square test (or Fisher's exact test) for categorical variables.

For efficacy analysis, between-group differences in continuous variables are tested using the independent t-test when data are normally distributed and the Mann-Whitney U test otherwise. Within-group differences between time points are tested using the paired t-test when data are normally distributed and the Wilcoxon signed rank test otherwise. Normality is assessed using the Shapiro-Wilk test. Where between-group differences exist in variables that may influence the primary endpoints, analysis of covariance is performed additionally with those variables as covariates.

For safety analysis, adverse events are classified by causality and severity, and the number of events is calculated. The number of participants and number of events are tabulated by type for adverse events, adverse reactions, and serious adverse events. Events are regarded as related to the study food unless classified as probably not related or definitely not related. For clinical laboratory values and vital signs, descriptive statistics (number of participants, mean, standard deviation, minimum, median, maximum) are presented for baseline, each visit, the final evaluation time point, and the change from baseline to the final evaluation time point. Contingency tables are presented for categorical data, and 95% confidence intervals are calculated where required.

Missing values in the ITT analysis are handled using multiple imputation.

ETHICS

The study is conducted in accordance with the Declaration of Helsinki, the study protocol, and applicable regulations. The protocol and any amendments are approved by the Institutional Review Board prior to implementation. Written informed consent is obtained from each participant after adequate explanation of the study content and of the compensation procedures for any health-related harm that may occur during the study. Participant confidentiality is protected through the use of identification codes in place of personal identifying information.

Inclusion criteria

• Adults, male or female, aged 20 to 70 years
• Body mass index of 25 kg/m2 or more and less than 30 kg/m2
• Meeting the Rome IV criteria for diarrhea-predominant irritable bowel syndrome (IBS-D), defined as Bristol Stool Form Scale type 6 or 7 in 25% or more of bowel movements from 2 weeks before screening through the day of the screening visit
• No inflammatory bowel disease or malignancy
• Provided written agreement to refrain from consuming kimchi-containing foods for the duration of the study (approximately 2 months)

Exclusion criteria

• Drug-induced constipation
• Constipation secondary to another condition, such as diabetes mellitus or thyroid disease
• History of intra-abdominal surgery other than appendectomy (including gastrectomy, gastric bypass, gallbladder or biliary tract surgery, pancreatectomy, bowel resection with particular reference to the ileum, and colorectal surgery or insertion procedures)
• Uncontrolled hypertension (resting blood pressure 160/100 mmHg or higher)
• Uncontrolled diabetes mellitus (fasting blood glucose 160 mg/dL or higher)
• Uncontrolled hypothyroidism or hyperthyroidism
• AST or ALT concentration 3 times or more the upper limit of the reference range of the testing laboratory
• Creatinine concentration 2 times or more the upper limit of the reference range of the testing laboratory
• Severe cardiovascular or cerebrovascular disease or malignancy within the previous 6 months
• Psychiatric disorder such as severe affective disorder, schizophrenia, or substance use disorder, or current use of related psychiatric medication (intermittent use for sleep disturbance is permitted)
• Severe alcohol use disorder
• Heavy smoking (20 cigarettes per day or more)
• Hypersensitivity to the main ingredient or components of the study food
• Severe gastrointestinal symptoms such as heartburn or dyspepsia
• Use of medications or foods that may affect the study results, including kimchi and probiotics
• For female volunteers, suspected pregnancy, lactation, or plan to become pregnant during the study period
• Participation in another drug clinical trial within one month prior to the screening date, or planned participation
• Judged unsuitable for participation by the principal investigator for reasons other than those listed above