Dietary fat and gut microbiota interactions determine diet-induced obesity in mice.

OBJECTIVE: Gut microbiota may promote positive energy balance; however, germfree mice can be either resistant or susceptible to diet-induced obesity (DIO) depending on the type of dietary intervention. We here sought to identify the dietary constituents that determine the susceptibility to body fat accretion in germfree (GF) mice. METHODS: GF and specific pathogen free (SPF) male C57BL/6N mice were fed high-fat diets either based on lard or palm oil for 4 wks. Mice were metabolically characterized at the end of the feeding trial. FT-ICR-MS and UPLC-TOF-MS were used for cecal as well as hepatic metabolite profiling and cecal bile acids quantification, respectively. Hepatic gene expression was examined by qRT-PCR and cecal gut microbiota of SPF mice was analyzed by high-throughput 16S rRNA gene sequencing. RESULTS: GF mice, but not SPF mice, were completely DIO resistant when fed a cholesterol-rich lard-based high-fat diet, whereas on a cholesterol-free palm oil-based high-fat diet, DIO was independent of gut microbiota. In GF lard-fed mice, DIO resistance was conveyed by increased energy expenditure, preferential carbohydrate oxidation, and increased fecal fat and energy excretion. Cecal metabolite profiling revealed a shift in bile acid and steroid metabolites in these lean mice, with a significant rise in 17ß-estradiol, which is known to stimulate energy expenditure and interfere with bile acid metabolism. Decreased cecal bile acid levels were associated with decreased hepatic expression of genes involved in bile acid synthesis. These metabolic adaptations were largely attenuated in GF mice fed the palm-oil based high-fat diet. We propose that an interaction of gut microbiota and cholesterol metabolism is essential for fat accretion in normal SPF mice fed cholesterol-rich lard as the main dietary fat source. This is supported by a positive correlation between bile acid levels and specific bacteria of the order Clostridiales (phylum Firmicutes) as a characteristic feature of normal SPF mice fed lard. CONCLUSIONS: In conclusion, our study identified dietary cholesterol as a candidate ingredient affecting the crosstalk between gut microbiota and host metabolism.

Gut barrier impairment by high-fat diet in mice depends on housing conditions.

SCOPE: Diet-induced obesity (DIO) is proposed to cause impairments in intestinal barrier integrity, but contradictory results have been published and it appears that the outcomes depend on other environmental factors. We therefore assessed whether the hygienic status of animal facilities alters the gut barrier in DIO mice. METHODS AND RESULTS: Male C57BL/6N mice were housed in a conventional (CV) or a specific pathogen-free (SPF) animal facility and were fed identical diets represented by a high-fat (60kJ% fat) or control diet (11kJ% fat) for 12 wks. Intestinal barrier function in small and large intestine was evaluated in Ussing chambers by electrical resistance and permeability measurements. Jejunal (p < 0.01) and proximal colonic (p < 0.05) barrier function was altered in CV DIO mice, but not in SPF DIO mice. Moreover, only CV DIO mice were characterized by metabolic endotoxemia and low-grade inflammation. High-throughput 16S rRNA gene sequencing revealed significant differences in fecal bacterial diversity and composition between the two animal facilities, but only in mice fed the HFD. Moreover, cecal DCA concentrations correlated positively with two yet uncultivated Clostridiales species. CONCLUSIONS: We demonstrated that housing conditions and associated changes in gut bacterial colonization are pivotal for maintenance of gut barrier integrity in DIO mice.

Diet-induced obesity causes metabolic impairment independent of alterations in gut barrier integrity.

SCOPE: The causal relationship between diet-induced obesity and metabolic disorders is not clear yet. One hypothesis is whether the obese state or high-fat diet per se affects intestinal barrier function provoking metabolic comorbidities. METHODS AND RESULTS: In three independent experiments with AKR/J, SWR/J, or BL/6J mice, we addressed the impact of genetic background, excess body fat storage, duration of high-fat feeding, and quality/quantity of dietary fat on glucose tolerance and gut barrier integrity in vivo and ex vivo. Impaired glucose tolerance in diet-induced obese BL/6J and AKR/J mice was not accompanied by an altered intestinal barrier function. Enforced dietary challenge by prolonged feeding and increasing fat quantity in BL/6J mice still failed to aggravate metabolic and intestinal deterioration. Despite a low-grade inflammatory status in adipose tissue, barrier function of BL/6J mice fed lard high-fat diet revealed no evidence for a diet-induced loss in barrier integrity. CONCLUSION: None of our results provided any evidence that gut barrier function is a subject to dietary regulation and obesity per se seems not to cause gut barrier impairment.