Anti-Obesity Effects of Dietary Fibers Extracted from Flaxseed Cake in Diet-Induced Obese Mice

Abstract

Although many efforts have been made to characterize the functional properties of flaxseed, knowledge concerning the properties of insoluble and soluble dietary fibers in flaxseed is still limited. Here, insoluble and soluble dietary fibers were extracted from flaxseed cake-a valuable resource that has not been fully exploited. Subsequently, their monosaccharide compositions, structural properties, and anti-obesity effects in male mice were characterized. The anti-obesity effects of flaxseed cake insoluble dietary fiber (FIDF), flaxseed cake soluble dietary fiber (FSDF), and FIDF combined with FSDF in diet-induced obese mice were investigated in our study. Supplementation with FSDF alone or FIDF and FSDF together lowered the fat accumulation, improved the serum lipid profile, increased the basal metabolism, and improved the gut microbiota of obese mice. Supplementation with FIDF and FSDF together significantly enriched the abundance of g_Akkermansia and g_Bifidobacterium, which are negatively associated with obesity. Supplementation with FIDF alone improved the liver lipid profile, raised the basal metabolism, and enhanced the short-chain fatty acid levels in the guts of the mice. In conclusion, our results collectively support the therapeutic potential of FIDF and FSDF in obesity treatment and indicate that FIDF and FSDF play different roles in the process of obesity treatment. Furthermore, our results provide critical information for flaxseed cake resource exploitation.

Keywords: flaxseed cake; gut microbiota; high-fat diet; insoluble dietary fiber; lipid accumulation; soluble dietary fiber.

Figure 1

SEM analyses of FSDF and FIDF at 10,000× and 5000× magnification. (A) FSDF × 10,000; (B) FSDF × 5000; (C) FIDF × 10,000; (D) FIDF × 5000.

Figure 2

Effects of FIDF and FSDF on obesity symptoms and plasma biochemical parameters. (A) Body weight. (B) Percentage of BAT, eWAT, and iWAT to body weight. (C) Liver weight. (D–H) Serum TC, TG, HDL-C, LDL-C, and TBA contents, respectively. CON, control group; HFD, high-fat diet group; FIDF, group supplemented with FIDF alone; FSDF, group supplemented with FSDF alone; MIX, group supplemented with FIDF and FSDF together. Data are expressed as mean ± SEM (n = 6). * p < 0.05; ** p < 0.01; *** p < 0.0001; **** p < 0.0001; ns, not significant.

Figure 3

Effects of FIDF and FSDF on hepatic lipid accumulation and hepatic histomorphology. (A) Liver TC content. (B) Liver TG content. (C) HE staining of liver sections in different groups (shown at 400× magnification). CON, control group; HFD, high-fat diet group; FIDF, group supplemented with FIDF alone; FSDF, group supplemented with FSDF alone; MIX, group supplemented with FIDF and FSDF together. Data are expressed as mean ± SEM (n = 6). * p < 0.05; ** p < 0.01; ns, not significant.

Figure 4

Effects of FIDF and FSDF on basal metabolism. The mice’s basal metabolism was measured by housing the mice in a twelve-chamber Comprehensive Laboratory Animal Monitoring System and using indirect calorimetry. (A) The 24 h light–dark cycle energy expenditure. (B) Total, light, and dark energy expenditure. (C) The 24 h light–dark cycle RER. (D) Total, light, and dark RER. (E) The 24 h light–dark cycle ambulatory activity. (F) Total, light, and dark ambulatory activity. CON, control group; HFD, high-fat diet group; FIDF, group supplemented with FIDF alone; FSDF, group supplemented with FSDF alone; MIX, group supplemented with FIDF and FSDF together. Data are expressed as mean ± SEM (n = 6). * p < 0.05; ** p < 0.01; *** p < 0.0001; **** p < 0.0001; ns, not significant.

Figure 5

Effects of FIDF and FSDF on intestinal flora composition. (A) Microbial distribution at the phylum level. (B) Chao index at the OTU level. (C) Shannon index at the OTU level. (D) Principal coordinate analysis (PCoA) based on OTU levels. CON, control group; HFD, high-fat diet group; FIDF, group supplemented with FIDF alone; FSDF, group supplemented with FSDF alone; MIX, group supplemented with FIDF and FSDF together. Data are expressed as mean ± SEM (n = 6). * p < 0.05; ** p < 0.01; *** p < 0.0001; ns, not significant.

Figure 6

The LEfSe analysis of gut microbiota (LDA scores > 4.0). The characteristic gut microbiota of the different groups are showed in the figure. CON, control group; HFD, high-fat diet group; FIDF, group supplemented with FIDF alone; FSDF, group supplemented with FSDF alone; MIX, group supplemented with FIDF and FSDF together.

Figure 7

Effects of FIDF and FSDF on SCFA production. Concentrations of (A) total SCFAs, (B) acetic acid, (C) propanoic acid, (D) isobutyric acid, (E) butyric acid, (F) isovaleric acid, and (G) pentanoic acid. CON, control group; HFD, high-fat diet group; FIDF, group supplemented with FIDF alone; FSDF, group supplemented with FSDF alone; MIX, group supplemented with FIDF and FSDF together. Data are expressed as mean ± SEM (n = 6). * p < 0.05; ** p < 0.01; *** p < 0.0001; **** p < 0.0001; ns, not significant.