Personalizing Intermittent Fasting: The Role of Microbiome Diversity and Fiber Intake in Shaping Health Outcomes

BACKGROUND: Intermittent fasting (IF) has been linked to improved metabolic health, reduced inflammation, and increased longevity in animal models. These effects are thought to be mediated through changes in the gut microbiome. Murine studies consistently show that IF enhances microbial diversity and promotes beneficial species like Lactobacillus and Bifidobacterium, improving metabolic profiles and gut barrier function. However, human studies reveal inconsistent results, suggesting that individual-level factors such as baseline microbiome composition and fiber intake may influence response to IF. HYPOTHESIS: Baseline gut microbiome diversity and habitual dietary fiber intake modulate the metabolic and inflammatory benefits of intermittent fasting in humans. METHODS: A systematic literature review was conducted to identify peer-reviewed research articles and clinical trials involving intermittent fasting, gut microbiome outcomes, and metabolic parameters in murine and human models. RESULTS: •Murine models: Consistent increase in microbial diversity and improvement in metabolic markers •Human studies: Highly variable outcomes; benefits more likely in individuals with diverse microbiomes and higher fiber intake •Few human trials stratify participants by microbiome composition or diet, limiting interpretation CONCLUSIONS: Individual variability in human IF outcomes may stem from differences in gut microbiome diversity and dietary fiber intake. A threshold model is proposed, in which individuals with favorable gut conditions are more responsive to IF. This supports the need for personalized dietary interventions.