Changes in the body weight and body fat

Figure 1 showed that the body weight of mice at the beginning and the end of dietary treatment. No significant differences were shown at the beginning of treatment in mice (all Ps > 0.05). At the 19th week, the body weights of mice in high-fat groups were all higher than that in the CON group (all Ps < 0.05). The weight of mice in the n-6 PUFA was significantly higher than that in the LCSFA, MCSFA, n-3 PUFA, MUFA, and TFA groups (all Ps < 0.05). Mice in the n-3 PUFA group had lower body weight than that in the MUFA group (P < 0.05). The body weight of mice in the TFA group was higher than that in the n-3 PUFA group (P < 0.05).

Fig. 1

Body weight of mice at the 0 and 19th week of intervention. n = 10, data expressed as the mean ± SD. a P < 0.05, compared to CON group; b: P < 0.05, compared to LCSFA group; c: P < 0.05, compared to MCSFA group; d: P < 0.05, compared to n-3 PUFA group; e: P < 0.05, compared to n-6 PUFA group

As shown in Fig. 2, compared with the CON group, mice had higher contents of perirenal fat, peri-testicular fat, and omental fat in high-fat groups (all Ps < 0.05). The perirenal fat in the n-6 PUFA group was higher than those in other groups (all Ps < 0.05). The perirenal fat in the LCSFA group was higher than that in the n-3 PUFA groups (P < 0.05). The peri-testicular fat in the LCSFA, n-6 PUFA, and TFA groups was higher than that in the n-3 PUFA group (P < 0.05). Compared to that in the n-6 PUFA group, the MCSFA and MUFA groups had lower peri-testicular fat contents (all Ps < 0.05). In addition, compared with that in the n-6 PUFA group, other groups had lower omental fat contents (all Ps < 0.05). The omental fat in the n-3 PUFA was lower than that in the LCSFA group (P < 0.05).

Fig. 2

Effect of diets on the body fat mass in obese mice. A Comparison of the levels of perirenal fat among the seven groups. B Comparison of the levels of peri-testicular fat among the seven groups. C Comparison of the levels of omental fat among the seven groups. n = 10, data expressed as the mean ± SD. a: P < 0.05, compared to CON group; b: P < 0.05, compared to LCSFA group; c: P < 0.05, compared to MCSFA group; d: P < 0.05, compared to n-3 PUFA group; e: P < 0.05, compared to n-6 PUFA group

In conclusion, the n-6 PUFA-rich diet had the greatest effect on the increase in the body weight and body fat of mice, while the n-3 PUFA-rich diet had the least effect.

Changes in the lipid profiles of plasma

As shown in Table 1, the lipid profiles in plasma of mice were assayed. Compared with those in the CON group, the concentrations of C18:2 n-6c, C20:4 n-6, total n-6 PUFA, and total PUFA increased in the LCSFA group. In contract, the concentrations of C22:0, C16:1, C18:1 n-9c, and total MUFA decreased in the LCSFA group; the concentrations of C12:0, C14:0, C16:1, C18:1 n-9c, total MUFA, and C18:2 n-6c increased in the MCSFA group (all Ps < 0.05). The concentrations of C18:2 n-6c, C18:3 n-3, C20:5 n-3, C22:6 n-3, total n-3 PUFA, and total PUFA in the n-3 PUFA group were higher than those in the CON group. Conversely, C16:0, C22:0, total SFA, C16:1, C18:1 n-9c, total MUFA, C20:3 n-6, C20:4 n-6, and n-6/n-3 PUFA of the n-3 PUFA group were lower (all Ps < 0.05). Compared with those in the CON group, the contents of C18:2 n-6c, total n-6 PUFA, C22:6 n-3, total n-3 PUFA, and total PUFA increased in the n-6 PUFA group. Conversely, the contents of C22:0, C16:1, C18:1 n-9c, and total MUFA decreased in the n-6 PUFA group. Compared with the CON group, the concentrations of C18:1 n-9c, total MUFA, C18:2 n-6c, C20:4 n-6, total n-6 PUFA, C22:6 n-3, total n-3 PUFA, and total PUFA increased, but C22:0, and C16:1 decreased in the MUFA group. Moreover, the contents of C18:2 n-6c, C20:4 n-6, total n-6 PUFA, C22:6 n-3, total n-3 PUFA, total PUFA, and C18:1 n-9t (TFA) in the TFA group were higher those that in the CON group, while C22:0 and C16:1 were lower than those in the CON group (all Ps < 0.05). In addition, according to the data in Table 1, we found that the contents of total SFA and the n-6/n-3 PUFA ratio were the highest, as well as the content of total n-3 PUFA was the lowest of the plasma in the MCSFA group. But the mice of the n-3 PUFA group presented the opposite situation.

Table 1 Effect of diets on the lipid profiles of plasmaChanges in the markers of intestinal barrier function

To determine the effect of different diets on the markers of intestinal barrier function, we examined the expression of claudin-1, claudin-5, occludin, and ZO-1 proteins in the ileum and colon of mice. The Western blotting results in Fig. 3 showed that the expression level of claudin-5 in ileum decreased in the MCSFA, n-3 PUFA, n-6 PUFA, MUFA, and TFA groups, compared with that in the CON group (all Ps < 0.05). The claudin-5 expressions in colon in the LCSFA, MCSFA, n-6 PUFA, and TFA groups were lower than that in the CON group (all Ps < 0.05). The claudin-5 expression in colon in the n-6 PUFA group was lower than those in the LCSFA, n-3 PUFA, and MUFA groups (all Ps < 0.05). The occludin expression in colon in the CON group was higher than those in the LCSFA and MCSFA groups (all Ps < 0.05). Compared with that in the MUFA group, the occludin expressions in colon were decreased in the LCSFA, MCSFA, n-6 PUFA, and TFA groups (all Ps < 0.05). The expression level of ZO-1 in ileum in the CON group was higher than those in the LCSFA, MCSFA, n-6 PUFA, MUFA, and TFA groups (all Ps < 0.05). Compared with that in the n-3 PUFA group, the expression levels of ZO-1 in ileum decreased in the MCSFA and TFA groups (all Ps < 0.05). Based on the effect of dietary fat composition, the alteration of gut tight junction proteins in the ileum among all groups showed a higher consistency than that in the colon. The former suggested that high MCSFA and TFA diets might cause stronger damage to mucosal barrier in ileum.

Fig. 3

Changes in the expression of tight junction proteins in ileum and colon. A The expression of claudin-1 in ileum was detected by Western blotting analysis. B The expression of claudin-5 in ileum. C The expression of occuldin in ileum. D The expression of ZO-1 in ileum. E The expression of claudin-1 in colon. F The expression of claudin-5 in colon. G The expression of occuldin in colon. H The expression of ZO-1 in colon. n = 3, data expressed as the mean ± SD. a: P < 0.05, compared to CON group; b: P < 0.05, compared to LCSFA group; c: P < 0.05, compared to MCSFA group; d: P < 0.05, compared to n-3 PUFA group; e: P < 0.05, compared to n-6 PUFA group; f: P < 0.05, compared to MUFA group

Changes in the BDNF and 5-HT of brain and intestine

As shown in Fig. 4, ELISA assay shows the protein expression levels of BDNF and 5-HT in brain, ileum, and colon. Compared with that in the CON group, the BDNF expression decreased in brain in other groups (all Ps < 0.05). The BDNF of brain in the MUFA group was lower than that in the TFA group (P < 0.05). Compared with that in the CON group, the BDNF of colon decreased in the LCFSA and MCSFA groups (all Ps < 0.05). The BDNF of colon in the n-3 PUFA group was higher than that in the MCSFA group (P < 0.05). The BDNF in colon in the n-6 PUFA group was lower than those in the CON, LCSFA, MCSFA, n-3 PUFA, and MUFA groups (all Ps < 0.05). Additionally, the BDNF of colon in the TFA group was lower than those in the CON, LCSFA, n-3 PUFA, and MUFA groups (all Ps < 0.05). The expression levels of 5-HT in brain decreased in the MUFA and TFA groups, compared with the CON group (all Ps < 0.05). Overall, the n-3 PUFA group displayed the least effect on BDNF and 5-HT in gut–brain axis.

Fig. 4

Changes in the protein levels of BDNF and 5-HT of brain, ileum, and colon. A The expression of BDNF in brain was detected by ELISA. B The expression of BDNF in ileum. C The expression of BDNF in colon. D The expression of 5-HT in brain. E The expression of 5-HT in ileum. F The expression of 5-HT in colon. n = 4, data expressed as the mean ± SD. a: P < 0.05, compared to CON group; b: P < 0.05, compared to LCSFA group; c: P < 0.05, compared to MCSFA group; d: P < 0.05, compared to n-3 PUFA group; e: P < 0.05, compared to n-6 PUFA group; f: P < 0.05, compared to MUFA group

Changes in the leptin, insulin, and ghrelin of hippocampus and intestine

As shown in Figs. 5, 6 and 7, immunohistochemical analysis demonstrates that the leptin immunoexpression in hippocampus in the MCSFA was lower than that in the n-3 PUFA group (P < 0.05). The leptin of hippocampus in the n-6 PUFA group was lower than that in the CON group (P < 0.05). The leptin in hippocampus decreased in the MUFA group, compared with those in the CON, LCSFA, MCSFA, and n-3 PUFA groups (all Ps < 0.05). The insulin expressions in hippocampus decreased in the LCSFA and MUFA groups, compared with those in the CON and TFA groups (all Ps < 0.05). Compared with that in the MCSFA group, the insulin in hippocampus decreased in other groups (all Ps < 0.05). Compared with that in the MCSFA group, the leptin in ileum decreased in other groups (all Ps < 0.05). The ghrelin of ileum in the CON group was higher than those in other groups (all Ps < 0.05). The ghrelin of ileum in the n-3 PUFA group was lower than that in the MCSFA group, in contract; it was higher than that in the MUFA group (both Ps < 0.05). The ghrelin in ileum increased in the LCSFA, MCSFA, and TFA groups, compared with those in the n-6 PUFA and MUFA groups (all Ps < 0.05). The leptin expressions of colon in the CON, n-3 PUFA, n-6 PUFA, and TFA groups were lower than those in the LCSFA, MCSFA, and MUFA groups (all Ps < 0.05). The leptin of colon in the n-3 PUFA group was higher than that in the n-6 PUFA group (P < 0.05). In addition, compared with that in the MCSFA group, the levels of ghrelin of colon were increased in the CON, LCSFA, n-3 PUFA, and n-6 PUFA groups (all Ps < 0.05). The ghrelin of colon in the MUFA group was lower than those in other groups (all Ps < 0.05). The ghrelin of colon in the TFA group was lower than those in the CON, n-3 PUFA, and n-6 PUFA groups (all Ps < 0.05). It was obvious of above results that high MCSFA diet might upregulate the insulin expression in hippocampus and the leptin in ileum of mice.

Fig. 5

Changes in the immunoexpression of leptin, insulin, and ghrelin in hippocampus. A The expressions of leptin, insulin, and ghrelin in hippocampus were evaluated by immunochemistry staining. The positivity was visualized in tan. B The immunoexpression of leptin in hippocampus. C The immunoexpression of insulin in hippocampus. D The immunoexpression of ghrelin in hippocampus. n = 3, data expressed as the mean ± SD. a: P < 0.05, compared to CON group; b: P < 0.05, compared to LCSFA group; c: P < 0.05, compared to MCSFA group; d: P < 0.05, compared to n-3 PUFA group; f: P < 0.05, compared to MUFA group

Fig. 6

Changes in the immunoexpression of leptin and ghrelin in ileum. A The expressions of leptin and ghrelin in ileum were evaluated by immunochemistry staining. The positivity was visualized in tan. B The immunoexpression of leptin in ileum. C The immunoexpression of ghrelin in ileum. n = 3, data expressed as the mean ± SD. a: P < 0.05, compared to CON group; b: P < 0.05, compared to LCSFA group; c: P < 0.05, compared to MCSFA group; d: P < 0.05, compared to n-3 PUFA group; e: P < 0.05, compared to n-6 PUFA group; f: P < 0.05, compared to MUFA group

Fig. 7

Changes in the immunoexpression of leptin and ghrelin in colon. A The expressions of leptin and ghrelin in colon were evaluated by immunochemistry staining. The positivity was visualized in tan. B The immunoexpression of leptin in colon. C The immunoexpression of ghrelin in colon. n = 3, data expressed as the mean ± SD. a: P < 0.05, compared to CON group; b: P < 0.05, compared to LCSFA group; c: P < 0.05, compared to MCSFA group; d: P < 0.05, compared to n-3 PUFA group; e: P < 0.05, compared to n-6 PUFA group; f: P < 0.05, compared to MUFA group