Korean fermented soybean paste (Doenjang) has anti-obesity and anti-hypertensive effects via the renin-angiotensin system (RAS) in high-fat diet-induced obese rats

The health-beneficial outcomes of doenjang, a Korean fermented food have been questioned due to its high salt content; moreover, the detailed underlying mechanisms of its health beneficial effects are not fully investigated. Thus, this study aimed to investigate doenjang's anti-obesity effects, anti-hypertensive effects, and its underlying mechanisms in high-fat diet -induced obesity. Sprague-Dawley rats fed with normal diet (ND), high-fat diet (HD), HD with 8% additive salt (HDS), or HD with doenjang containing 8% salt (HDJ) for 13 weeks. Compared to HD and HDS groups, the HDJ group had lower body and epididymal fat tissue weight gain and showed hypotrophy and hypoplasia. The RAS-related mRNA levels in the adipose tissue, including Renin and Ace were downregulated in the HDJ group compared to HD and HDS groups. Additionally, HDJ groups had significant improvements in systolic blood pressure, serum RAS-associated parameters (e.g., angiotensin II and aldosterone), renal mRNA levels related to RAS (e.g., angiotensin II receptor type 1 and 2), and aldosterone-associated mRNA expressions (e.g., mineralocorticoid receptor) in the kidney of HD-induced obese rats. Most importantly, HDS and HDJ groups showed distinct outcomes regarding adipogenesis and electrolytes metabolism, even though both diets contain a high level of salt. HDS group showed a higher epididymal fat tissue weight, mass, and adipocyte size than HDJ group. In addition, compared with HDJ group, HDS group significantly decreased the release of Na+ and K+ throughout the urine and feces. The present study addresses that doenjang has anti-obesity effects and anti-hypertensive effects by activating RAS in the adipose tissue and kidney, respectively. Additionally, this study also demonstrates that salt in doenjang and the additive salt differently influences adipogenesis and electrolytes metabolism, supporting doenjang has health advantageous effects regardless of its high salt contents.