Kimchi improves irritable bowel syndrome: results of a randomized, double-blind placebo-controlled study.

Irritable bowel syndrome (IBS) can be caused by abnormal bowel movements, altered brain-gut axis, gut microbiota change, and low levels of inflammation or immune activation. The intake of food containing much fiber and lactic acid bacteria (LABs) can alleviate IBS. This study was undertaken to confirm the alleviative effect of kimchi on symptoms of IBS. Three types of kimchi (standard kimchi, SK; dead nano-sized Lactobacillus plantarum nF1 (nLp) added to standard kimchi, nLpSK; or functional kimchi, FK) were given to 30 individuals in each of three groups, that is, the SK group (n = 30), the nLpSK group (n = 30), or the FK group (n = 30) at 210 g a day for 12 weeks. Food intake records, serum levels of inflammatory factors, fecal levels of harmful enzymes, and microbiome changes were investigated over the 12-week study period. After intervention, dietary fiber intake was increased in all groups. Typical IBS symptoms (abdominal pain or inconvenience, desperation, incomplete evacuation, and bloating), defecation time, and stool type were also improved. In serum, all groups showed reductions in tumor necrosis factor (TNF)-α (P < 0.001) levels. In addition, serum IL-4 (P < 0.001), IL-10 (P < 0.001), and IL-12 (P < 0.01) were significantly reduced in the nLpSK and FK groups, and serum monocyte chemotactic protein (MCP)-1 (P < 0.05) was significantly reduced in the nLpSK group. Furthermore, activities of fecal β-glucosidase and β-glucuronidase were significantly decreased in all three groups, and these reductions were greatest in the nLpSK group. Gut microbiome analysis showed that kimchi consumption increased Firmicutes populations at the expense of Bacteroidetes and Tenericutes populations. In addition, the Bifidobacterium adolescentis population increased significantly in the FK group (P = 0.026). Kimchi intake helps alleviate IBS by increasing dietary fiber intake and reducing serum inflammatory cytokine levels and harmful fecal enzyme activities. Notably, nLp improved the immune system, and several functional ingredients in FK promoted the growth of Bifidobacterium adolescentis in gut.