Intake of Watermelon or Its Byproducts Alters Glucose Metabolism, the Microbiome, and Hepatic Proinflammatory Metabolites in High-Fat-Fed Male C57BL/6 J Mice

Abstract

Background: Watermelon intake has demonstrated effects on blood pressure regulation along with other health benefits.

Objective: We hypothesized that intake of whole watermelon and products made from watermelon rind (WR) and watermelon skin (WS) would remediate metabolic complications in C57BL/6 J male mice fed a diet modeling a Western-style diet.

Methods: Ten-week-old male C57BL/6 J mice were provided either a low-fat (LF) diet [10% fat (by energy), 8% sucrose (by energy) and no added cholesterol], a high-fat (HF) diet [45% fat (by energy), 20% kcal sucrose (by energy), and 1% (w/w) cholesterol], or an HF diet plus WS, WR, or watermelon flesh (WF) for 10 wk. Dried WF was provided at 8% of total energy (equivalent to 2 servings/d) and watermelon skin and rind were added at 2.25% (w/w, dry weight of additives) of diet. Animals were provided experimental diets ad libitum. Body weights, food intake, and glucose tolerance were determined. Serum insulin, inflammatory markers, microbiome, and the relative hepatic concentrations of 709 biochemicals were measured postmortem.

Results: The final body weight of the LF control group was significantly lower than that of the HF-fed control group (32.8 ± 0.9 g compared with 43.0 ± 1.7 g, P ≤ 0.05). Mice in treatment groups fed HF supplemented with watermelon products had final body weights similar to those of the HF-fed control mice. Serum insulin concentrations were reduced by ∼40% in mice fed an HF diet with WR supplementation compared with mice fed an HF diet alone (P ≤ 0.05). Depending on the individual species or group, microbiome populations changed significantly. Supplementation with WF resulted in a return to the basal hepatic concentrations of monohydroxy fatty acids and eicosanoids observed in LF-fed mice (P ≤ 0.05).

Conclusions: In obese male mice, supplementation with each of the watermelon products to an HF diet improved fasting blood glucose, circulating serum insulin concentrations, and changes in hepatic metabolite accumulation. At a modest level of supplementation to an HF diet, fiber-rich additives made from WR and WS further improved glucose metabolism and energy efficiency and shifted the microbiome composition.

Keywords: C57BL/6 J mice; diabetes; fiber; glucose metabolism; high-fat diet; value-added food; watermelon.