Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter with beneficial effects including antihypertension and antistress properties. In this study, we examined the effects of GABA-enriched white rice (GABA rice) on blood pressure (BP) in 39 mildly hypertensive adults in a randomized, double-blind, placebo-controlled study. The participants were divided into a test group (n = 22) who consumed rice with 11.2 mg GABA/100 g of rice and a placebo group (n = 17) who consumed rice with 2.7 mg GABA/100 g of rice. For 8 weeks, the participants took 150 g of either the GABA rice or the placebo rice. Hematological examinations were performed on both groups at 0, 4, and 8 weeks after the start of rice consumption. Home BP was self-measured two times daily, morning and evening, from 1 weeks before to 2 weeks after the intervention. Although the hospital BP and evening BP measurements of the participants showed no significant change, consumption of the GABA rice improved the morning BP compared with the placebo rice after the 1st week and during the 6th and 8th weeks. These results showed the possibility that the GABA rice improves morning hypertension.

To identify optimal conditions of GABA Enriching Equipment for making GABA enriched high eating quality whiterice (GABA rice), we measured the GABA contents in whiterice and performed sensory evaluation and volatile compounds analysis of cooked rice, using the Hokkaido rice cultivar Yumepirika. Quantity of GABA included in GABA rice following a 3-hours enrichment had much about 10 times of normal whiterice at 11. 4 mg/100 g of whiterice. Sensory and volatile analysis of cooked rice showed that GABA rice following a >4-hours enrichment process had distinctive grassy and raw smells. Therefore, we concluded that a 3-hours enrichment process was the most suitable for GABA rice. The stress relief effects of GABA rice in humans were investigated in a randomized, placebo-controlled, double-blind clinical trial.Thirty-nine adult subjects were enrolled in this study and were divided into the following two groups : GABA rice or placebo whiterice; 150 g of whiterice was fed daily for eight weeks. VAS tests revealed that the mental condition and quality of sleep tended to improve by the intake of GABA rice. In addition, blood cortisol and adiponectin levels indicated that stress load tended to be lighten by GABA rice. In conclusion, the intake of GABA rice with a 3-hours enrichment process is effective for gently lightening the stress load.