The Anti-Obesity Effect of Fish Oil in Diet-Induced Obese Mice Occurs via Both Decreased Food Intake and the Induction of Heat Production Genes in Brown but Not White Adipose Tissue

Abstract

Omega-3 (ω-3) polyunsaturated fatty acids in fish oil have been shown to prevent diet-induced obesity in lean mice and to promote heat production in adipose tissue. However, the effects of fish oil on obese animals remain unclear. This study investigated the effects of fish oil in obese mice. C57BL/6J mice were fed a lard-based high-fat diet (LD) for 8 weeks and then assigned to either a fish oil-based high-fat diet (FOD) or continued the LD for additional 8 weeks. A control group was fed a standard diet for 16 weeks. Mice fed the FOD showed weight loss, reduced adipose tissue mass, and lower plasma insulin and leptin levels compared to those fed the LD. Rectal temperatures were higher in the FOD and LD groups compared to the control group. Energy intake was lower in the FOD group than the LD group but similar to the control group. The FOD and LD groups exhibited increased expression of heat-producing genes such as Ppargc1a, Ucp1, Adrb3, and Ppara in brown adipose tissue but not in white adipose tissue. The FOD reduced food consumption and increased rectal temperature and heat-producing genes in brown adipose tissue. Fish oil may therefore be a potential therapeutic approach to obesity.

Keywords: brown adipose tissue; diet-induced obesity; omega-3 polyunsaturated fatty acids; white adipose tissue.

Figure 1

Fish oil prevents dietary fat-induced increases in body weight in mice with diet-induced obesity. (a) Experimental protocol: Five-week-old male C57BL/6J mice were fed a control diet (CD) or a lard-based high-fat diet (LD) for 8 weeks. (b) Body weight; (c) body weight gain between 12 and 20 weeks of age. The CD contained 9% calories from fat, 21% calories from protein, and 70% calories from carbohydrates (3.8 kcal/g); the LD and a fish oil-based high-fat diet (FOD) contained 60% calories from fat, 21% calories from protein, and 19% calories from carbohydrates (5.3 kcal/g). Food was provided to the mice every other day. The data are presented as the mean ± standard error of the mean, n = 4–6 animals per group * p < 0.05, ** p < 0.01, *** p < 0.001 compared with the CD group, ‡ p < 0.05, ‡‡ p < 0.01, ‡‡‡ p < 0.001 compared with the LD group using one-way ANOVA with Tukey’s or Games–Howell multiple comparisons post hoc test based on Levene’s test results.

Figure 2

Fish oil prevents dietary fat-induced increases in adipose tissue mass and food intake while maintaining rectal temperature in mice with diet-induced obesity. (a) Mesenteric adipose tissue (Mes) mass; (b) inguinal adipose tissue (Ing) mass; (c) epididymal adipose tissue (Epi) mass; (d) liver mass; (e) representative Oil red O-stained liver histology; (f) food intake; (g) average food intake between 13 and 20 weeks of age; (h) body temperature; (i) average body temperature between 13 and 20 weeks of age. The data are presented as the mean ± standard error of the mean, n = 4–6 animals per group. * p < 0.05, ** p < 0.01, *** p < 0.001 compared with the CD group; ‡ p < 0.05, ‡‡ p < 0.01, ‡‡‡ p < 0.001 compared with the LD group using a one-way ANOVA with Tukey’s or Games–Howell multiple comparisons post hoc test based on Levene’s test results. DIO, diet-induced obesity; LD, lard-based high-fat diet; CD, control diet; FOD, fish oil-based high-fat diet.

Figure 3

High-fat diets increase the expression of heat-producing genes in brown adipose tissue (BAT). The expression of genes involved in heat production increased in the BAT of mice fed the LD and the FOD. Gene expression levels in BAT. (a) Adrb3; (b) Prdm16; (c) Ppargc1a; (d) Ppara; (e) Pparg; (f) Ucp1; (g) Fgf21; (h) Klb; (i) Ffar4. The data are presented as the mean ± standard error of the mean, n = 6 animals per group. * p < 0.05, ** p < 0.01, *** p < 0.001 compared with the CD group, ‡ p < 0.05, ‡‡ p < 0.01, ‡‡‡ p < 0.001 compared with the LD group using a one-way ANOVA with Tukey’s or Games–Howell multiple comparisons post hoc test based on Levene’s test results. BAT, brown adipose tissue; CD, control diet; LD, lard-based high-fat diet; FOD, fish-oil based high-fat diet; Adrb3, β₃-adrenergic receptor; Prdm16, PR domain containing 16; Ppargc1a, peroxisome proliferator-activated receptor-γ coactivator-1α; Ppara, peroxisome proliferator-activated receptor-α; Pparg, peroxisome proliferator-activated receptor-γ; Ucp1, uncoupling protein 1; Fgf21, fibroblast growth factor 21; Klb, βklotho; Ffar4, free fatty acid receptor 4.

Figure 4

High-fat diets do not increase the expression of heat-producing genes in inguinal white adipose tissue (WAT). No changes in gene expression were observed in inguinal WAT. (a) Adrb3; (b) Prdm16; (c) Ppargc1a; (d) Ppara; (e) Pparg; (f) Ucp1; (g) Fgf21; (h) Klb; (i) Ffar4. The data are presented as the mean ± standard error of the mean, n = 6 animals per group. WAT, white adipose tissue; CD, control diet; LD, lard-based high-fat diet; FOD, fish-oil based high-fat diet; Adrb3, β₃-adrenergic receptor; Prdm16, PR domain containing 16; Ppargc1a, peroxisome proliferator-activated receptor-γ coactivator-1α; Ppara, peroxisome proliferator-activated receptor-α; Pparg, peroxisome proliferator-activated receptor-γ; Ucp1, uncoupling protein 1; Fgf21, fibroblast growth factor 21; Klb, βklotho; Ffar4, free fatty acid receptor 4.

Figure 5

Fish oil improves glucose tolerance and insulin resistance in mice with diet-induced obesity. Mice were dissected at 21 weeks. (a) Changes in blood glucose, as indicated by the GTT. (b) AUC of blood glucose levels during the GTT. (c) Changes in plasma insulin, as indicated by the GTT. (d) AUC of plasma insulin levels during the GTT. (e) Changes in blood glucose, as indicated by the ITT. (f) AUC of blood glucose levels during the ITT. The data are presented as the mean ± standard error of the mean, n = 4–8 animals per group. * p < 0.05, ** p < 0.01, *** p < 0.001 compared with the CD group, ‡ p < 0.05, ‡‡ p < 0.01, ‡‡‡ p <0.001 compared with the LD group using a one-way ANOVA with Tukey’s or Games–Howell multiple comparisons post hoc test based on Levene’s test results. CD, control diet; LD, lard-based high-fat diet; FOD, fish oil-based high-fat diet; ITT, insulin tolerance test; AUC, area under the curve; GTT, glucose tolerance test.