Forty-four female students with a tendency for constipation (mean age, 20.2±3.3 y) were asked to consume 30 g test pickles daily for 2 wk and were divided into 3 groups: viable-cell intake subjects (n=14, 3.0×10⁵ colony-forming units of viable LAB (lactic acid bacteria) cells per sample), dead-cells intake subjects (n=15, viable cells were heat sterilized), and placebo-intake subjects (n=15, LAB removed from the pickles). γ-Aminobutyric acid content of 75.1±3.2 mg per sample was noted, with no marked difference between samples containing viable and dead cells. Natural killer (NK)-cell activity (% specific lysis) in serum from dead-cell intake subjects was 37.5±17.0% before the start of the test-food intake and 47.7±20.1% after intake, indicating statistically significant effects (p<0.01). However, viable-cell intake and placebo intake subjects showed no statistically significant difference. The number of days with bowel movements significantly increased from 3.8±1.5 to 4.9±1.8 d in the dead-cell intake group, whereas a slight change from 4.6±1.5 to 5.1±1.7 d was observed in the viable-cell intake group. Additionally, the feeling of incomplete evacuation fell and a refreshed feeling increased among the subjects with constipation. Thus, marked enhancement of NK-cell activity and improved bowel symptoms were observed in subjects consuming pickles containing dead LAB cells.