Reducing sodium intake is crucial for preventing and managing hypertension, a leading cause of global mortality. High sodium intake is strongly correlated with high blood pressure. Despite recommendations for significant salt reduction (e.g., <6 g/day in Japan, <5 g/day by the WHO), average daily salt intake remains far higher in many countries. Salt reduction initiatives often face challenges due to a decrease in food palatability. This study addresses this issue by investigating whether the addition of umami, specifically MSG, can enhance the palatability of low-sodium soup, a common food item worldwide. Previous research suggests the potential of umami substances to offset the negative palatability effects of salt reduction; however, these studies often had limitations in sample size and regional representation. The current research aims to validate the impact of MSG on saltiness and palatability across a large, diverse Japanese population, thereby providing evidence-based support for effective salt reduction strategies.

Extensive research links high sodium intake to increased blood pressure and cardiovascular diseases. Numerous studies and meta-analyses confirm this positive correlation. Global initiatives, including the World Health Organization's (WHO) targets for salt reduction, highlight the urgency of addressing high sodium consumption. While numerous countries have implemented salt reduction programs, the success rate is often limited due to the significant impact on palatability. Studies have shown that reducing salt content in food can significantly decrease its appeal, making it difficult for people to adhere to low-sodium diets. The challenge of maintaining palatability while reducing salt has led to research into potential flavor enhancers, particularly umami compounds like MSG and CDG. Previous studies using various broths have shown promise, but often lack sufficient sample sizes or diverse geographic representation. This paper addresses these limitations through its large-scale, multi-regional approach.

This multicenter study (2017-2018) involved 584 participants (after exclusions) from 19 regions in Japan. Participants included students from eight universities and attendees of 11 health seminars. Six aqueous solutions were prepared: three NaCl concentrations (0.3%, 0.6%, 0.9%) with and without 0.3% MSG. The solutions were randomly coded (A-F). Sensory evaluations were conducted using a visual analog scale (VAS) to assess saltiness and palatability. Each participant tasted all six solutions twice, with a 15-minute or more interval and a change in the order of presentation between the two evaluations. The average of the two evaluations was used for analysis. Participants also completed questionnaires detailing demographics, smoking habits, fasting time, and medication use. Statistical analysis was conducted using repeated measures ANOVA and Tukey's HSD post-hoc test for pairwise comparisons. Ethical approval was obtained from relevant institutional review boards.

Saltiness ratings increased significantly with NaCl concentration. The 0.3% NaCl solution with MSG had significantly higher saltiness ratings than the 0.3% NaCl solution without MSG (39.1 ± 0.7 vs. 23.5 ± 0.6 mm, p < 0.0001). At the 0.6% NaCl level, MSG slightly increased saltiness (p = 0.0070). No significant difference was observed at the 0.9% NaCl level. Palatability ratings were significantly higher for solutions with MSG across all NaCl concentrations. The 0.3% NaCl solution with MSG had almost twice the palatability rating compared to the 0.3% NaCl solution without MSG and was significantly higher than the other five solutions. The findings remained consistent across different demographic groups (sex, age, region, smoking status, fasting time, and medication use), although some subgroup analyses revealed subtle variations in the saltiness enhancement effect of MSG.

The results strongly support the hypothesis that umami can compensate for the palatability loss caused by salt reduction in soup. The significant enhancement of palatability, especially at the 0.3% NaCl concentration with MSG, suggests that a substantial reduction in sodium is possible without sacrificing consumer acceptance. The consistency of these findings across diverse demographic groups increases the generalizability of the results. These findings have important implications for public health strategies to reduce sodium intake. By incorporating umami enhancers such as MSG, food manufacturers can reduce sodium content without compromising palatability, thereby promoting healthier dietary choices and assisting in managing hypertension and other sodium-related health issues.

This study demonstrates that adding 0.3% MSG to soup significantly enhances palatability, especially at lower NaCl concentrations (0.3%). This allows for substantial salt reduction (from 0.9% to 0.3%) without negative impacts on palatability, providing a practical approach for public health initiatives aimed at reducing sodium intake. Future research could explore the optimal MSG concentration for different types of soups and other food products, and investigate the long-term effects of umami-enhanced low-sodium diets on blood pressure and overall health.

While the study had a large sample size and broad geographic representation, it focused solely on aqueous solutions. The findings may not be directly generalizable to all types of soup, as the base ingredients (broths, vegetables, etc.) could influence the interaction between NaCl, MSG, and palatability. Furthermore, the study used a single type of umami enhancer; investigating other umami compounds or combinations might reveal additional possibilities for salt reduction.