Modified Mediterranean-ketogenic diet modulates gut microbiome and short-chain fatty acids in association with Alzheimer's disease markers in subjects with mild cognitive impairment

Abstract

Background: Alzheimer's disease (AD) prevalence is increasing, but its etiology remains elusive. Gut microbes can contribute to AD pathology and may help identifying novel markers and therapies against AD. Herein, we examine how the gut microbiome differs in older adults with mild cognitive impairment compared to cognitively normal counterparts, and whether and how a modified Mediterranean-ketogenic diet (MMKD) alters the gut microbiome signature in association with cerebrospinal fluid (CSF) AD biomarkers.

Methods: A randomized, double-blind, cross-over, single-center pilot study of MMKD versus American Heart Association Diet (AHAD) intervention is performed on 17 subjects (age: 64.6 ± 6.4 yr), of which 11 have mild cognitive impairment, while 6 are cognitively normal. Subjects undergo MMKD and AHAD intervention for 6-weeks separated by 6-weeks washout periods. Gut microbiome, fecal short-chain fatty acids (SCFAs), and markers of AD in CSF including amyloid β (Aβ)-40 and Aß-42, total tau, and phosphorylated tau-181 (tau-p181) are measured at before and after diet interventions.

Findings: At baseline, subjects with normal vs. impaired cognition show no notable difference in microbiome diversity but several unique microbial signatures are detected in subjects with mild cognitive impairment. Proteobacteria correlate positively with Aβ-42: Aβ-40 while fecal propionate and butyrate correlates negatively with Aβ-42 in subjects with mild cognitive impairment. Several bacteria are differently affected by the two diets with distinct patterns between cognitively normal and impaired subjects. Notably, the abundance of Enterobacteriaceae, Akkermansia, Slackia, Christensenellaceae and Erysipelotriaceae increases while that of Bifidobacterium and Lachnobacterium reduces on MMKD, while AHAD increases Mollicutes. MMKD slightly reduces fecal lactate and acetate while increasing propionate and butyrate. Conversely, AHAD increases acetate and propionate while reducing butyrate.

Interpretation: The data suggest that specific gut microbial signatures may depict the mild cognitive impairment and that the MMKD can modulate the gut microbiome and metabolites in association with improved AD biomarkers in CSF.

Keywords: Alzheimer; Dementia; Diet; High fat; Ketogenic; Microbiota; Nutrition; Short-chain fatty acids.

Fig. 1

Differences in the gut microbiome between subjects clinically diagnosed with mild cognitive impairment (MCI) versus cognitively normal (CN) counterparts. (a) Microbiome beta-diversity in terms of weighted unifrac distance, and (b-c) gut microbiome composition at the level of major phyla (b) and families (c) in CN (n = 6) and MCI subjects (n = 11). (d-l) Differences in the relative abundance of bacterial taxa in the gut microbiome of CN versus MCI subjects (*p < .05); (m-n): Linear discriminant analysis (LDA) effect size (Lefse) plot and cladogram representing the unique bacterial signatures identified in CN and MCI subjects.

Fig. 2

Gut bacterial taxa and fecal organic acids correlate with cerebral spinal fluid (CSF) biomarkers of Alzheimer's disease (AD) differently in subjects clinically diagnosed with mild cognitive impairment (MCI) versus cognitively normal (CN) counterparts. (a-d) Fecal concentration of organic acids including lactate and short-chain fatty acids in CN (n = 6) versus MCI subjects (n = 11). (e) Correlation (Spearman R; *p < .05) of gut bacterial taxa and fecal organic acids with CSF biomarkers of AD in CN versus MCI subjects.

Fig. 3

Mediterranean-style ketogenic diet (MMKD) and American Heart Association Diet (AHAD) differently influence gut microbiome in subjects clinically diagnosed with mild cognitive impairment (MCI) versus cognitively normal (CN) counterparts. (a-b) Phyla-level gut microbiome composition at baseline and endpoint of 6-weeks MMKD and AHAD intervention in all participants (n = 17) (a) and separately in CN (n = 6) versus MCI subjects (n = 11) (b). (c) Hierarchical clustering heat-map of gut bacterial taxa that showed >1.0 or < −1.0 Log₂-fold increase or decrease in relative abundance during MMKD or AHAD intervention. (d) Heat-map summarizing the differential patterns of diet-induced alterations (mean Log₂-fold change in relative abundance) in gut bacterial taxa that showed >1.0 or < −1.0 Log₂-fold increase or decrease in relative abundance during MMKD or AHAD intervention in CN and MCI subjects.

Fig. 4

Mediterranean-style ketogenic diet (MMKD) and American Heart Association Diet (AHAD) induce specific changes in the gut microbiome of subjects clinically diagnosed with mild cognitive impairment (MCI) versus cognitively normal (CN) counterparts. Mean Log₂-fold change in the relative abundance of major phyla (a), families (b) and genera (c) in CN (n = 6) versus MCI subjects (n = 11) (*p < .05).

Fig. 5

Differential effects of Mediterranean-style ketogenic diet (MMKD) and American Heart Association Diet (AHAD) on the functional analysis of the gut microbiome. Functional content of the gut microbiota was inferred by using PICRUSt based on the baseline and endpoint 16S amplicon sequencing data. Changes in the functional KEGG pathways during each dietary intervention were calculated by comparing the relative abundance of the KEGG orthologs and pathways (Level 2 and 3) at baseline vs. endpoint data and were interpreted in the form of mean Log₂-fold change.

Fig. 6

Mediterranean-style ketogenic diet (MMKD) and American Heart Association Diet (AHAD) differently influence gut microbial metabolites in subjects clinically diagnosed with mild cognitive impairment (MCI) versus cognitively normal (CN) counterparts. Mean percent change in the fecal concentration of intestinal organic acids in all participants (n = 17) (a-d) and separately in CN (n = 6) versus MCI subjects (n = 11) (e-h) (*p < .05).

Fig. 7

Diet-induced changes in gut microbiome and fecal organic acids are associated with changes in cerebral spinal fluid (CSF) biomarkers of Alzheimer's disease (AD) in subjects clinically diagnosed with mild cognitive impairment (MCI) versus cognitively normal (CN) counterparts. Heat-map depicting the correlation patterns (Spearman R; *p < .05) of changes (percent-fold) in gut bacterial taxa and fecal organic acids with changes (percent-fold) in CSF biomarkers of AD in CN (n = 6) versus MCI subjects (n = 11) (e-h).