Stress Condition on a Restricted Sodium Diet Using Umami Substance (L-Glutamate) in a Pilot Randomized Cross-Over Study

Hypertensive patients who adopt a sodium-restricted diet have difficulty maintaining this change, and this could increase stress. On the other hand, soup rich in umami substances (dashi) was reported to reduce indexes of anxiety and stress. The objective of this study was to measure mood and physiological stress indexes during administration of a sodium-restricted diet with and without an umami substance (free L-glutamate) by a cross-over randomized, single-blind, placebo-controlled trial in Japanese female university students. The baseline was measured for 5 days followed by a sodium-restricted diet intervention phase that lasted for 10 days. The Profile of Mood States questionnaire was administered, a stress marker in saliva (chromogranin-A) was measured, and the amount of sodium intake was confirmed from 24 h urine collection samples. Results showed that the sodium reduction was verified by 24 h urine excretion. The percentage of change in the stress marker from the baseline showed that the stress level in group without the umami substance was significantly higher than that in the group with the umami substance (p = 0.013) after receiving a sodium-reduced diet for 6 or more days, indicating that stress was alleviated. This study suggested that umami substances might help to ameliorate stress during a sodium-reduced diet, especially in the initial phase.