Our results provided evidence that (1) HFD-induced colonic dysbiosis is associated with weight gain, which was significantly reversed by the short-term dietary switch from an HFD to a normal balanced CD; (2) both an SHFD or an LHFD could lead to colonic dysbiosis with an increase in the abundances of Peptococcaceae and Akkermansiaceae families; (3) the increased in the abundance of Bacteriodes acidifaciens and decreased of Lachnospiraceae NK4A136 group in the DS. (Fig. 3a-c); (4) No changes in blood lipid profiles and liver function were found in DS mice in comparison with the control group. These results suggest that the correction of HFD-induced dysbiosis through dietary modification may be a pivotal factor for the maintenance of physiological homeostasis, and the potential health problem caused by obesity could be partially resolved by dietary changes.
The formula of HFDs was diverse and affected microbiota differentially [43]. In general, obesity was linked to a 50% reduction in the abundance of Bacteroidetes in mice and humans [17, 19, 20]. Furthermore, this change was reversed after weight loss [19]. A HFD can increase Firmicutes and decrease Bacteroidetes in the human gut [44]. Tang et al have been reported that the abundances of Erysipelotrichaceae, Family_XIII, Ruminococcaceae, ratAN060301C, Clostridiales Coprococcus, Intestinimonas, Parabacteroides, Pseudobutyrivibrio, and Roseburia are increased after HFD feeding. Some microbes such as Defluviitaleaceae, Defluviitaleaceae, Lachnospiraceae, Peptococcaceae, vadinBB60, Christensenellaceae, Coriobacteriaceae, Peptostreptococcaceae, Prevotellaceae, RF9, Ruminococcaceae, and S24-7 (Muribaculaceae) are decreased after a HFD feeding [45]. Ruminococcus, Akkermannsia, Bacteroidetes, Faecalibacterium, Bifidobaterium, Lactobacillus and Blautia are positively corelated to type 2 diabetes. Furthermore, Rumonococcus and Fusobacterium are negatively correlated to type 2 diabetes [46]. These microbes involves in the gut permeability, metabolism, and inflammation in directly or in directly way [46]. In our study, we also found that the decreased proportions of Bacteroidetes, and Muribaculaceae and the increased proportions of Akkermansia, Parabacteroides, Intestinimonas, and Roseburia (Fig. 6a-d and Additional file 1) indicating our HFD feeding was workable. However, the abundance of Peptococcaceae was increased in SHFD and LHFD which might because of the differences of HFD formula (Fig. 6a-d, 7a) [43]. In the current study, we found that the diet shifting could restore an imbalanced microbiota. However, some genera were still affected even after the dietary shift, such as Acetatifactor, Ruminiclostridium, GCA−900066575, Ruminiclostridium 5, Ruminococcaceae UCG−004, Lachnospiraceae UCG−006, Intestinimonas, and Lachnospiraceae AC2044 group labeled as C2 (Additional file 1). Some genera might also be affected by the dietary shift, such as Roseburia, Anaerotruncus, Oscillibacter, Marvinbryantia, and Lachnospiraceae UCG−001 labeled as C4 (Additional file 1). The functions of these genera remain unclear at present. They might play roles in the homeostasis of nutrition, metabolism, and even the immune system. Further study on their functions is warranted.
The function of Lachnospiraceae NK4A136 group is not clear. In HFD mice, Lachnospiraceae NK4A136 group is reduced and negatively correlates to triglyceride [39]. Instead, Liu et al have been reported that the abundance of Lachnospiraceae NK4A136 group has no effect at high-fat diet-fed mice; however, it elevates after fed with a sulfated polysaccharide from Gracilaria Lemaneiformis [40]. The diverse data might be due to the ingredients of HFD and the duration for HFD feeding. Lachnospiraceae NK4A136 group positively correlates to bile acids indicating it involving in cholesterol homeostasis [40]. Zhang et al have found that the abundance of Lachnospiraceae NK4A136 group increases in type 2 diabetes mellitus rat and returns to the level as the control after fed with anthraquinone-glycoside [42]. Moreover, obese mice with fucosylated chondroitin sulphate feeding showed the anti-inflammation effects as well as the elevation of Lachnospiraceae NK4A136 group [41]. In our study, the abundance of Lachnospiraceae NK4A136 group decreased during HFD feeding and returned to the level as NDC mice after fed with CD (Fig. 6 and 7e) suggesting that it might be a potential probiotic. Lachnospiraceae NK4A136 group needs further investigation in the following study.
High fiber dietary is a factor to influence gut microbiota and produce SCFAs to regulating metabolism by gut microbiota [47]. High fiber diet significantly elevated microbes, involving SCFA production, such as Lachnospira, Akkermannsia, Bifidobacterium, Lactobacillus, Ruminococcus, Roseburia, Clostridium, Faecalibacterium, and Dorea [30]. In our study, the proportions of Bacteriodes acidifaciens and Akkermansiaceae family were increased significantly in mice fed with either an SHFD or an LHFD (Fig.6a-d, 8c, and 8d). Moreover, a 3-month CD shift could not restore the level of Bacteriodes acidifaciens (Fig. 7 and 8d). Bacteriodes acidifaciens has been reported that it prevents obesity and improves insulin sensitivity [32] and its abundance elevates in the high fiber dietary [31, 48]. In our study, CD dietary contained 5.3 % crude fiber, 15.4 % neutral detergent fiber, and 6.3 % acid detergent fiber. The fiber in HFD was 6.5 % and derived from powdered cellulose. The composition of fiber was different between CD and HFD. The abundance of Bacteriodes acidifaciens was increased in the DS group might be affected by the fibers or HFD (Fig. 6 and 8d). After the dietary shift, abundance of Bacteriodes acidifaciens was still significantly higher in the DS group (Fig. 7 and 8d). It indicates that Bacteriodes acidifaciens was not easy to be affected by CD. he mucus-degrading A. muciniphila, which belongs to the Akkermansiaceae family, utilizes colonic mucus as a carbohydrate source and is associated with increased pathogen susceptibility through enhanced bacterial colonization in the epithelium when mice were fed with a fiber-free diet [36]. A. muciniphila also increased in mice receiving a red meat–mimic heme diet, leading to colonic mucolysis [37]. An HFD as well as red meat-free and fiber-free diets are risk factors for colorectal cancer; however, the mechanism is under-investigated. Although reports have indicated that increased A. muciniphila may have beneficial effects on obese mice,[49] our study provides new insights into the role of Akkermansiaceae bacterial in mice receiving an HFD. At the endpoint, the lipids level and adipokines were similar between the NDC and DS groups (Fig. 3d, 3d, 9a-c). Bacteriodes acidifaciens and Akkermansiaceae family might help the homeostasis of lipids level and adipokines [32].
An HFD has several effects on animal anatomy and physiology and results in pathological changes. Although HFD-fed mice exhibited increased blood lipids, their liver function was not affected [50]. In the current study, histology of the liver revealed similar morphologies in the DS and NDC mice (Fig. 9g). The DS and NDC mice also exhibited similar blood lipid levels. Moreover, although TCHO, HDL, and TG levels decreased in the DS mice, this decreased level was not significant (Fig. 9a-c). We further examined adipokines, leptin, and adiponectin (Fig. 3d and 3e). Studies have reported elevated leptin and unchanged adiponectin in the serum of HFD-fed mice [51, 52]. The results of the present study indicated that gut length and blood lipid levels were restored in the DS mice.
Despite these findings, our study has some limitations. Sample sizes for determining the microbiota pattern after LHFD and dietary shifts were small (N = 3 for NDC and N = 5 for DS). The mice were maintained in a relatively simple environment, which enabled their physiology and microbiota to be restored more through the dietary shift to a regular balanced diet. In this study, we only investigated the dominant bacteria. Some minor species that play critical roles may have been overlooked. However, we attempted to provide an overall observation of the condition of the DS group. Hopefully, this information can inspire researchers to investigate therapies to counteract the effects of HFD.