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Literature Review | Good News for Patients with Diabetes: Cognitive Impairment May Be Reversible! Intermittent Fasting Alleviates Cognitive Dysfunction Caused by Diabetes

Introduction:

Cognitive decline is a serious complication of type 2 diabetes, with multifactorial etiology.

Researchers have found that a 28-day intermittent fasting regimen can ameliorate behavioral deficits by modulating the microbiota–metabolite–brain axis: intermittent fasting enhances the expression of genes involved in mitochondrial biogenesis and energy metabolism in the hippocampus, reshapes the gut microbiota, and concurrently elevates microbial metabolites associated with cognitive function. Furthermore, the researchers identified close interconnections among the genes, microbes, and metabolites affected by intermittent fasting.

In this article, we will take a detailed look at how intermittent fasting can improve cognitive impairment.

This issue’s literature review

 

Research Background:

The global prevalence of type 2 diabetes (T2D) is steadily increasing. Cognitive decline represents a serious complication of T2D, with its underlying pathogenesis attributed to multiple factors, including cerebral insulin resistance, microvascular damage, and neuroinflammation. Previous studies have demonstrated that T2D‑related or high‑fat‑induced cognitive deficits are associated with cerebral insulin resistance, reduced glucose uptake, dysregulated neurotransmitter metabolism, and mitochondrial dysfunction.

Intermittent fasting (IF) is a periodic fasting regimen that can effectively improve metabolism and alleviate insulin resistance and other symptoms of type 2 diabetes (T2D). It has also demonstrated neuroprotective effects and cognitive enhancement in certain animal models; however, its protective role against T2D‑induced cognitive impairment remains unclear.

Here, researchers found that a 28-day intermittent fasting regimen can ameliorate behavioral deficits via the microbiota–metabolite–brain axis: IF enhances the expression of genes involved in mitochondrial biogenesis and energy metabolism in the hippocampus, reshapes the gut microbiota, and concurrently modulates microbial metabolites associated with cognitive function.

Moreover, researchers have identified close links among the genes, gut microbes, and metabolites influenced by IF. Depleting gut microbiota with antibodies can partially abolish the neuroprotective effects of IF. With respect to enhancing cognitive function, IPA, 5-HT, SCFAs, and TUDCA exhibit effects comparable to those of an IF diet.

 

Experimental Design:

Experimental Procedure

Main conclusions:

1.  IF inhibits insulin resistance and cognitive impairment.

Spontaneously diabetic db/db mice were divided into two groups and subjected to either ad libitum feeding (hereafter referred to as AL) or intermittent fasting (hereafter referred to as IF) for a period of 28 days. Normal db/m mice on an AL diet served as the control group. The results showed that IF reduced body weight in db/db mice without altering total energy intake. Furthermore, at the end of the intervention, IF markedly decreased daily water intake and urine output in db/db mice.

On day 28, an insulin tolerance test was used to assess the effects of intermittent fasting (IF) on insulin resistance in db/db mice. Compared with mice on an ad libitum (AL) diet, IF treatment improved insulin sensitivity by reducing fasting blood glucose levels by 54.8% and fasting insulin levels by 29.8%. Following IF treatment, the HOMA-IR index, which reflects insulin resistance, was decreased in db/db mice. Furthermore, IF significantly reduced both the mass of epididymal white adipose tissue (eWAT) and the size of adipocytes.

The Morris water maze test demonstrated that intermittent fasting (IF) treatment improves cognitive function and enhances spatial memory in diabetic mice. Results from the elevated plus-maze assay indicated that IF therapy ameliorates anxiety-like behaviors and locomotor activity in db/db mice.

Figure 1. Intermittent fasting alleviates insulin resistance and cognitive impairment in DB/DB mice.

 

2.  IF improves synaptic ultrastructure and insulin signaling.

Following euthanasia of the mice, the ultrastructure of hippocampal synapses—regions implicated in cognition and memory—was examined. Post-synaptic density (PSD) analysis revealed that, compared with the db/db group, both the length and width of PSDs were increased in the db/db-IF group.

Evaluation of insulin signaling in the hippocampus revealed that IF increased phosphorylation of IRS1-Tyr896 and Akt, indicating activation of the hippocampal insulin signaling pathway. Furthermore, compared with db/db mice, IF treatment enhanced the expression of BDNF—a neurotrophic factor involved in maintaining neuronal survival and synaptic function—and boosted ERK/CREB phosphorylation, an upstream signal for BDNF synthesis. Similarly, in the hippocampus of IF‑treated mice, the expression of PSD‑95, a scaffolding protein in the postsynaptic density of excitatory synapses, was also elevated, consistent with alterations in the ultrastructure of the PSD.

It is also noteworthy that the key transcription factor NF-κB, which mediates inflammation, is activated in the hippocampus of diabetic mice, whereas IF treatment inhibits NF-κB activation and downregulates the phosphorylation of JNK and p38 as well as the protein expression of Iba‑1.

Figure 2. Intermittent fasting improves the synaptic ultrastructure in the brains of db/db mice and modulates IRS/Akt and CREB/ERK signaling pathways.

 

3.  IF promotes mitochondrial biogenesis in the hippocampus.

To identify the key biological processes and pathways regulated by IF in the hippocampus, RNA sequencing was performed on the mouse hippocampus. Compared with db/db and db/m mice, 1,181 genes were found to be highly expressed in db/db‑IF mice, most of which were enriched in mitochondria‑related GO terms. Analysis of GO terms for genes downregulated in db/db mice revealed dysregulation of respiratory chain activity and mitochondrial fission/translation processes, suggesting mitochondrial metabolic abnormalities in the hippocampus of diabetic mice. However, the regulatory alterations associated with mitochondrial gene expression were reversed following IF treatment.

Furthermore, following IF treatment, the expression levels of 483 genes in the hippocampus of db/db mice were comparable to those in db/m mice; indeed, 31.3% of these genes exhibited higher expression (60 genes) or lower expression (91 genes) relative to db/m mice. IF also enhanced the expression of mitochondrial genes, thereby upregulating genes associated with the KEGG oxidative phosphorylation (OXPHOS) pathway. KEGG analysis of these genes further revealed that IF treatment restored the expression of OXPHOS‑related energy‑metabolism genes that had been downregulated in db/db mice. Weighted Gene Co‑Expression Network Analysis (WGCNA) identified five modules comprising functionally and biologically interconnected genes.

qPCR analysis confirmed that, in db/db mice, IF upregulated the expression of mitochondrial and metabolic genes. As an indicator of mitochondrial biogenesis, the mtDNA/nDNA ratio in the hippocampus of db/db mice was elevated by IF, suggesting that the upregulation of mitochondrial genes may reflect an increase in mitochondrial mass.

Furthermore, by assessing the expression of PGC1α and AMPK/mTOR proteins, we sought to elucidate the underlying mechanisms responsible for the upregulation of mitochondrial biogenesis in the db/db-IF group. Intermittent fasting (IF) elicited a marked increase in the expression of PGC1α, a key regulator of mitochondrial biogenesis, which was strongly correlated with the upregulation of mitochondria‑related genes.

Consistent with previous studies, IF increased AMPK activity—this kinase is sensitive to cellular energy metabolism under fasting conditions—and inhibited mTOR phosphorylation. mTOR is a nutrient sensor in eukaryotic cells that plays a critical role in regulating mitochondrial quality control and oxidative phosphorylation (OXPHOS).

Figure 3. Intermittent fasting improves energy metabolism and mitochondrial biogenesis in the hippocampus.

 

4.  IF reshapes the gut microbiota and microbial metabolites.

The integrity of the intestinal barrier is essential for maintaining intestinal permeability and preventing endotoxemia, and it is also associated with diabetes and its complications. It has been reported that increased intestinal permeability can lead to endotoxemia, which in turn exacerbates inflammation and triggers impaired glucose tolerance.

Accordingly, the effects of IF on intestinal barrier integrity were investigated by assessing villus length, muscularis thickness, and goblet cell density. The results showed that IF increased villus length and muscularis thickness in diabetic mice, but did not affect goblet cell numbers. Measurements of colonic permeability indicated that IF attenuated intestinal leakage, accompanied by a reduction in plasma LPS levels. Furthermore, the expression of the tight junction protein claudin‑1 was elevated in the colonic tissue of db/db mice treated with IF, consistent with the observed changes in intestinal permeability.

At day 0 (baseline) and day 28, the gut microbiota composition in mouse fecal samples was assessed using 16S rRNA sequencing. The results showed that although the total number of OTUs remained at the initial level, α-diversity significantly increased after 28 days of IF treatment. At day 28, the unweighted UniFrac distances of db/db‑IF mice differed from those of the other groups, indicating that IF therapy also altered β‑diversity.

Taking time as a confounding factor, diet and the rodent genotype were the primary determinants of gut microbiome composition, accounting for 5.9% and 7.7% of the total variance, respectively. IF treatment did not fully offset the effects of diabetes. Allobaculum and Bifidobacterium The relative abundance of was reduced in db/db mice. However, IF treatment improved Lactobacillus and propionate-producing bacteria Odoribacter the abundance, while Enterococcus 、 Streptococcus and unknown Enterococcaceae were reduced. Compared with the db/db group, in the db/m and db/db-IF groups, from Candidatus Arthromitus 、 Rummeliibacillus , the levels of bacteria from the families Enterococcaceae and Leuconostocaceae were both low.

Furthermore, the identified IF‑related genera are associated with obesity, as well as with blood glucose and body weight—factors linked to cognition. Specifically, Candidatus Arthromitus Unknown Leucostocaceae and blood glucose were positively correlated (Pearson correlation coefficients of 0.52 and 0.72, respectively; p < 0.05). Unknown Enterococcaceae was positively correlated with body weight (Pearson correlation coefficient = 0.59; p < 0.05).

Taking into account the influence of mouse genetic background, the gut microbiota composition of mice in the db/db and db/db-IF groups was assessed on day 28. A total of 17 zOTUs were found to be affected by IF, of which 5 belonged to Lactobacillus Meanwhile, PICRUSt analysis revealed 11 distinct KEGG gene pathways that were significantly enriched. Notably, in the db/db-IF group, the biosynthesis of primary and secondary bile acids was markedly enriched.

To investigate the effects of intermittent fasting (IF) on the gut microbiota and host metabolism, researchers employed untargeted metabolomics and found that, after 28 days of IF treatment, numerous metabolites in the plasma of db/db mice exhibited significant changes. Notably, they focused on a predefined subset of 23 microbial metabolites whose levels are predominantly modulated by the abundance of the gut microbiota, thereby demonstrating a direct link among IF treatment, the gut microbiota, and the metabolome.

Among these metabolites, compared with the AL‑treated db/db mice, the IF‑treated group exhibited elevated plasma levels of 5‑HT, tryptophan, p‑hydroxyphenylacetic acid, N‑acetyltryptophan, cinnamoylglycine, IPA, and bile acids—including cholic acid (CA), deoxycholic acid (DCA), lithocholic acid (MCA), and TUDCA. In contrast, the db/db‑IF group showed lower levels of tyrosine, phenylacetylglycine, phenylpropionylglycine, methylphenol, p‑cresol sulfate, and 12‑hydroxyeicosapentaenoic acid (12‑HEPE) than the db/db group.

Short-chain fatty acids (SCFAs) have been shown to protect intestinal barrier function and modulate insulin sensitivity; accordingly, the researchers also analyzed SCFA concentrations in fecal samples. After 28 days of treatment, IF improved acetate, propionate, and butyrate levels in db/db mice. However, plasma SCFA concentrations were very low, making them undetectable by the non-targeted metabolomics approach employed in this study.

Figure 4. Analysis of gut microbiota and plasma metabolomics in db/db mice subjected to intermittent fasting.

 

5. Comprehensive Multi-Omics Analysis of IF Therapy

After identifying the distinct omics signatures that are upregulated or downregulated by IF in diabetic mice, the next step was to assess the interplay among hippocampal gene expression, gut microbiota composition, and microbial metabolites, linking these interactions to the effects of IF treatment on cognitive deficits observed in the mice. Multivariate dimensionality reduction and discriminant analysis—specifically, the DIABLO method—was employed to analyze the multi-omics data; this approach is designed to pinpoint biologically relevant, highly correlated features across diverse omics platforms.

Prior to performing multi-omics integration, we first assessed whether the IF‑upregulated hub genes (n = 36), IF‑altered OTUs (n = 17), pre‑identified plasma microbial metabolites (n = 23), and three fecal SCFAs—acetate, butyrate, and propionate—could predict the mice’s IF status in a multivariate framework.

Predictive modeling was performed using partial least squares discriminant analysis and integrated into a repeated double‑cross‑validation framework (rdCV‑PLSDA), effectively reducing the risk of overfitting. Significant separation was achieved between db/db and db/db‑IF mice, with prediction accuracies of 100% for hub genes, 90% for OTUs, and 95% for metabolites. For each omics dataset, the optimal number of latent components was one. The constructed model outperformed 1,000 permutation models, demonstrating its robustness and validity in distinguishing db/db from db/db‑IF; moreover, it relies on a parsimonious set of omics features, exhibiting strong generalizability.

Subsequently, a comprehensive model was constructed using multi-omics features, and a latent component was identified from each omics dataset, comprising 10 key predictive factors that yielded substantial separation between db/db and db/db-IF. The optimal set of key predictive factors included several gut microbial taxa, namely: Lactobacillus 、 Bacteroides and Facklamia , microbial co-metabolites such as bile acids, IPA, 5-HT, tryptophan, hydroxyindole phenol, and indoxyl sulfate, as well as genes enriched in mitochondrial, ribosomal, or metabolism-related GO terms. The key predictive factors are also highly correlated.

Figure 5. Multi-omics integrated modeling strategy and model performance associated with IF treatment

 

6. The beneficial effects of IF require the gut microbiota.

To demonstrate the critical role of the gut microbiota in mediating cognitive deficits in type 2 diabetes, researchers sought to determine whether the beneficial effects observed with IF would be impaired following depletion of the gut microbiota in db/db mice.

Antibiotic cocktail therapy was employed to elucidate the role of the microbiota in the neuroprotective effects of intermittent fasting (IF). Antibiotics were administered in the drinking water 14 days prior to the onset of 4-week IF treatment and throughout the experimental period, with behavioral changes assessed after 28 days. Antibiotic treatment attenuated the weight‑loss benefits of IF. While antibiotic administration had no effect on eWAT weight, it increased liver and cecal weights. Both IF and antibiotic treatment reduced food and water intake in db/db mice; however, antibiotic use did not compromise the beneficial effects of IF on insulin resistance.

Notably, the cognitive improvements assessed using the Morris water maze were associated with IF and were partially reversed by antibiotic treatment. Furthermore, in db/db-IF mice, antibiotic administration abolished the upregulation of mitochondrial biogenesis. Analysis of PSDs revealed that antibiotic treatment reduced PSD width in db/db-IF mice. Taken together, these findings suggest that depletion of the gut microbiota partially attenuates the protective effects of IF on cognitive function.

Furthermore, compared with the db/db-IF group, depletion of the gut microbiota via antibiotic treatment significantly reduced plasma IPA levels and fecal SCFA levels in db/db mice.

Figure 6. Effects of antibiotics and microbial metabolites on cognitive function in IF‑treated db/db mice.

 

7. Gut microbiota metabolites improve cognitive function

In addition, another animal study was conducted to investigate the role of IF in modulating gut microbiota–derived metabolites—particularly IPA and SCFAs, which were reduced in the antibiotic‑treated group—in ameliorating cognitive deficits. Furthermore, the effects of peripheral 5-HT and TUDCA on cognitive function were examined, as this study demonstrated that these metabolites were elevated in the IF group. Previous research has also reported their potential neuroprotective effects.

In db/db mice, oral administration of each of these metabolites individually improved cognitive function and insulin sensitivity. Consistent with the beneficial effects of IF treatment, oral administration of these metabolites also enhanced mitochondrial biogenesis and preserved synaptic ultrastructure. Furthermore, TUDCA treatment suppressed weight gain in db/db mice, whereas the other tested metabolites did not. In addition, none of the metabolite treatments affected food or water intake in db/db mice. Although the doses of these metabolites were higher than those used in the IF‑treated group, these findings partially elucidate the causal relationships and mechanisms underlying the effects of these metabolites in the context of IF therapy.

 

Summary:

A growing body of research indicates that intermittent fasting (IF) exerts beneficial effects on diabetes and its complications by reshaping the gut microbiota. However, it remains unclear whether IF can ameliorate diabetes‑related cognitive deficits and what role it plays in modulating the gut microbiota, underscoring the urgent need to investigate the underlying mechanisms by which IF improves cognitive function.

This study conducts a comprehensive investigation of behavioral and synaptic structural changes, as well as mitochondrial and energy metabolism–related signaling pathways, in diabetic mice, and… Integrative multi-omics analysis has, for the first time, demonstrated that 28-day intermittent fasting can ameliorate diabetes‑induced cognitive impairment via the microbiota–metabolite–brain axis. 。

Overall, current research indicates that in diabetic mice following IF treatment, the gut microbiota establishes a novel and compelling link between microbial metabolites and cognitive function. IF therapy can reshape the gut microbiota and alter its metabolic profiles, upregulate mitochondrial biogenesis and energy metabolism in the hippocampus, preserve synaptic ultrastructure, and ameliorate deficits in cognition and spatial memory. The effects of IF on microbial composition, metabolite profiles, and gene expression should be further evaluated in clinical trials. Once validated, IF could serve as a novel ecological intervention for managing metabolic and neurodegenerative disorders.

 

 

 

Reference Information:

[Journal Name]: Nature Communications

[Impact Factor]: IF = 12.121

[Therapeutic Approach]: Intermittent Fasting (IF)

[Disease]: Cognitive Impairment Caused by Type 2 Diabetes

[Sample Type]: Mouse Animal Model

[Technical Approach]: 16S rRNA sequencing + non-targeted metabolomics + transcriptomics

[Is there microbiome validation?]: Yes

[Key Microbial Community]: Lactobacillus, Odoribacter

 

 

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Supervising Producer  | Solar wind, always

Editor-in-chief  | Lemon

Editor-in-chief  | Little Swallow

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Editor  |  Lemon

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