The Impact of a Western Diet with High Salt on Metabolic Outcomes in Male C57bl/6J Mice

The Western diet promotes obesity and metabolic disease by increasing caloric intake and systemic inflammation. The typical Western diet is high in saturated fats, sugars, and salt. In pre-clinical rodent studies, the "Western" diet (also called the high-fat high-sucrose diet (HFHS)) is high in saturated fats and sugars (typically sucrose) but low in salt (<1% salt). As such, we sought investigate the impact of a chronic 3% NaCl Western diet (high-fat, high-sucrose + high salt (HFHS + Salt)) diet on systemic organ metabolism, liver mitochondrial function, and adipose tissue.

Thirty-six 8 week-old C57Bl/6J male mice were fed either a low-fat diet (LFD), a HFHS, or a HFHS + Salt diet for 16 weeks. Body weight, body composition, and food intake were monitored weekly. Glucose tolerance tests (GTT) and insulin concentrations were measured after 8 weeks of diet intervention to assess glucose and insulin homeostasis. Mice were euthanized at 16 weeks for liver mitochondrial respiration and tissue analysis.

Over 16 weeks, the HFHS fed group gained significantly more weight than the other diet groups. Liver weights were similar in LFD and HFHS + Salt groups but higher in the HFHS group. Liver triglycerides (TAGs) were also similar between LFD and HFHS + Salt groups, while HFHS had elevated liver TAGs. Inguinal and brown adipose tissue depots were larger in both HFHS and HFHS + Salt vs. LFD. Surprisingly, the gonadal adipose tissue was significantly larger in the HFHS + Salt compared to HFHS and LFD groups - suggesting that a HFHS + Salt exacerbates gonadal adipose expansion more than typical rodent HFHS. Paradoxically, the addition of salt appears to have dampened expression of inflammation related genes (Ccl2 & Adgre1) in adipose tissue compared to HFHS alone. Metabolically, the HFHS+ Salt fed mice showed the highest glucose intolerance, followed by HFHS and then LFD groups. Liver mitochondrial respiration, assessed by changing ATP/ADP ratios, showed the HFHS group with the highest oxygen consumption, followed by HFHS + Salt, then LFD groups, highlighting differences in respiration with additional salt (HFHS vs HFHS + Salt).

While the excess salt mitigated some HFHS effects on weight gain and hepatic lipid accumulation, it exacerbated gonadal adipose expansion and impaired glucose tolerance. HFHS increased mitochondrial respiration, but salt addition appeared to dampen this effect. Dietary salt, within a high-fat/high-sucrose context, has differential impacts on metabolic outcomes compared to HFHS alone, underscoring the need for further research to fully understand how Western diets (high-fat, high-sucrose, and high salt) impact all aspects of metabolic health.