Regulating the rhythm of ileal flora, the 8-hour diet weight loss method has scientific basis

In recent years, scientists have paid more and more attention to intestinal flora, and many diseases are closely related to intestinal flora imbalance. Intestinal flora refers to the microorganisms in the human intestine. Different species of bacteria can synthesize different vitamins necessary for human growth and development, synthesize amino acids with protein residues, participate in the metabolism of carbohydrates and proteins, and promote the absorption of mineral elements. They play a vital role in many physiological processes.

Recent studies have suggested that an additional role of the gut microbiome is to coordinate intestinal and hepatic circadian rhythms.

Diet and feeding/fasting cycles drive diurnal oscillations in gut microbial communities and secondary metabolites in the gut lumen. These oscillations are required for the expression of peripheral circadian clocks and associated liver and intestinal metabolic regulators that control glucose, cholesterol, and fatty acid homeostasis and host metabolic health. However, there is a drawback to using gut microbiome depletion models to study the relationship between the gut microbiome and peripheral circadian clocks. This model approach cannot explain whether diet-induced perturbations in microbial community dynamics affect host metabolism through circadian desynchronization.

Time-restricted feeding (TRF) has numerous benefits for host metabolic health. In a mouse high-fat diet model (regardless of the obesogenic diet fed), TRF reduced obesity, inflammation, improved glucose tolerance and cholesterol homeostasis, and reversed pre-existing metabolic syndrome. Most studies of the gut microbiome have focused on the large intestine or a more accessible surrogate, the feces. However, other regions of the intestine play a more important role in the host's metabolic homeostasis, especially the ileum, which has unique digestive and absorptive functions and microbial composition. Despite this, few studies have highlighted the importance of the ileal microbiota and its impact on host metabolic health.

On July 5, 2022, scientists from the University of California and other institutions published a long research article titled "Diet and feeding pattern modulate diurnal dynamics of the ileal microbiome and transcriptome" in Cell Reports. The team systematically analyzed the composition of the ileal microbiota and the dynamic changes of the transcriptome under normal diet, high-fat diet, and time-restricted high-fat diet conditions to determine the effects of high-fat diet and eating time on the types and circadian rhythms of the ileal microbiota.

The researchers first analyzed the effects of HFD and TRF on ileal microbial composition and circadian rhythm. Ileal samples were collected from three groups of mice fed a restricted high-fat diet (FT), a free high-fat diet (FA), and a normal diet (NA) at different time points every day to study the diurnal dynamics of the intestinal lumen and adherent bacteria.

The results showed that TRF could improve body weight and blood glucose levels induced by a high-fat diet when the calories of food were the same. A high-fat diet significantly reduced the a-diversity and β-diversity of ileal flora. There was little difference in the microbiome composition between mice in the restricted high-fat diet group and the free high-fat diet group, indicating that the type of diet affected the composition of the ileal microbiome more than the feeding method. Lactococcus and Erysipelothrix were enriched in the free high-fat diet group than in the restricted high-fat diet group. In addition, the richness of microorganisms that maintained rhythmic oscillations in mice on a free high-fat diet was less than half that of mice in the normal diet group, while mice on a restricted high-fat diet showed similar levels of periodic fluctuations as mice in the control group, indicating that the microbial circadian rhythm is related to the benefits of TRF on metabolic function.

The research team studied the relative abundance of ileal microbiota over time under different feeding and eating conditions in order to clarify the periodic oscillations of ileal microbial communities and determine their importance in host metabolism. The results showed that the dominant bacterial genus in all experimental conditions was Firmicutes, and lactic acid bacteria were found in all experimental groups, and their abundance was greatly reduced during the active period (dark period) of mice under high-fat feeding conditions. In addition, Staphylococcus aureus in mice in the normal diet group and the time-restricted high-fat diet group showed a rapid increase at the beginning of the dark period.

The researchers then explored whether host rhythmic genes affect ileal microbiota composition and circadian rhythms. The researchers used Cry1;Cry2 double knockout mice (CDKO) to test whether circadian clock genes are important for microbiome dynamics. Microbial rhythms in the ileum of CDKO-NA mice completely disappeared, and PCoA analysis reflected the disrupted feeding and sleeping rhythms of these mice. The most common bacteria found in the ileum belonged to the Erysipelothrix family and the Lactobacillus family. These results indicate that the host molecular circadian clock is related to the ileal dynamics of the microbiota, and interfering with the host circadian clock may disrupt the circadian rhythm of the ileal microbiota by interfering with eating patterns.

Because the daily dynamics of the microbiome influence the liver transcriptome, we hypothesized that the ileal transcriptome would also be affected by luminal oscillations. Transcripts were significantly reduced in the HFD compared with NA, but partially maintained in FT. 1862 protein-coding genes with circadian cycles overlapped among the three feeding groups. HFD disrupted rhythms in free-flowing HFD mice by inducing a phase shift toward the light, whereas TRF maintained these transcripts in FT mice. This suggests that rhythmic luminal dynamics are associated with circadian regulation of the host peripheral clock by TRF. Enrichment analysis of common periodic genes between mice fed a normal diet and a restricted HFD diet revealed associations with phospholipid metabolism, autophagy, and circadian rhythms, with HFD disrupting major circadian genes including Rev-erb, Per3, Clock, Bmal1, and Cry1, all of which remained unchanged in TRF.

The differences in mouse ileum samples under different diets and housing conditions may indicate that metabolic phenotype alone does not determine ileal transcriptional activity. TRF had a greater effect on gene expression, such as increased numbers of ileal DE genes in FT and FA compared with NA and FA. HFD disrupted the dynamic diurnal changes in the DE gene transcriptome.

The expression levels of genes involved in the immune response to bacteria were reduced in the high-fat diet FA, especially ⍺-defensins.

TRF improves insulin sensitivity and obesity in HFD mice. So how does eating pattern affect intestinal metabolic signaling pathways in the context of the gut microbiome and ileal clock maintaining circadian oscillations? The researchers found that a high-fat diet disrupts GLP-1 (a major blood glucose-regulating ileal hormone) and bile acid signaling pathways, but a TRF diet can reverse the damaged signaling pathways. Gcg and Dpp4 expression levels decreased and lost circadian rhythms when on a free high-fat diet. However, TRF maintained the circadian dynamics of both and caused changes in the gene expression of other transporters involved in GLP-1 signal transduction. In addition, bile acid pools, transport, reabsorption, and signaling were also impaired in the free high-fat diet group, but could still be reversed by TRF.

In summary, compositional oscillations of the gut microbiome are critical for normal peripheral circadian rhythms, both of which are disrupted in diet-induced obesity (DIO). Although time-restricted feeding (TRF) maintained circadian synchrony and prevented the occurrence of DIO, it had little effect on the dynamics of the cecal gut microbiota. Therefore, other regions of the intestine, particularly the ileum, a hub of incretin and bile acid signaling, may play an important role in influencing peripheral circadian rhythms. This study demonstrated the effects of diet and feeding rhythms on the composition and transcriptome of the ileum microbiome in mice. DIO suppressed the dynamic rhythms of the ileal microbiome composition and transcriptome. TRF partially restored the circadian rhythms of the ileal microbiome and transcriptome, increased the release of GLP-1, and altered the ileal bile acid pool and FXR signaling, which may explain how TRF exerts its metabolic benefits.

This study provides sufficient data to explore the circadian rhythm of the ileal microbiome and transcriptome, providing a scientific basis for fully understanding the important role of the ileum in the relationship between intestinal flora and disease occurrence, and also opens the journey of the ileum in the stage of intestinal flora.

References:

Diet and feeding pattern modulate diurnal dynamics of the ileal microbiome and transcriptome. Cell Rep. 2022 Jul 5;40(1):111008. doi: 10.1016/j.celrep.2022.111008.