The impact of very-low-calorie ketogenic diets on gut microbiota in individuals with obesity: a systematic review and meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of clinical intervention studies
PubMed 41054273 · doi:10.1080/19490976.2025.2566305
What was done
A systematic review and meta-analysis searched PubMed, EBSCOhost, Cochrane Library, and Web of Science through June 2025 to evaluate the impact of very-low-calorie ketogenic diets (VLCKD) on gut microbiota in individuals with obesity. A total of 14 studies were included. Random-effects meta-analyses and subgroup analyses based on baseline body mass index, age, and intervention duration evaluated changes in microbial alpha-diversity and relative taxon abundances.
What was found
VLCKD significantly increased microbial alpha-diversity, measured by Shannon index (SMD: 0.54, 95% CI: 0.03 to 1.04, P = 0.0378) and Faith's Phylogenetic Diversity index (SMD: 0.77, 95% CI: 0.36 to 1.18, P = 0.0002). For specific taxa, VLCKD significantly increased the abundance of Akkermansia (SMD: 1.76, 95% CI: 0.48 to 3.03, P = 0.0069) and the Firmicutes-to-Bacteroidetes ratio (SMD: 1.01, 95% CI: 0.67 to 1.34, P < 0.0001), while significantly decreasing Bifidobacterium abundance (SMD: -1.23, 95% CI: -1.81 to -0.64, P < 0.0001). Subgroup analyses showed Shannon index increases were more pronounced with BMI <= 30 kg/m2 and age > 30 years. Akkermansia increases were largest in participants with BMI 30-35 kg/m2, age > 40 years, and duration <= 6 weeks. Bifidobacterium reductions were marked in those with BMI 30-35 kg/m2, age > 40 years, and duration <= 12 weeks.
Why it matters
This review quantifies the specific microbial shifts caused by VLCKD in obesity, demonstrating that while overall diversity and Akkermansia increase, beneficial Bifidobacterium populations decline substantially. It highlights the need to weigh potential adverse microbial ecological shifts against metabolic benefits.
Limits
The total number of participants across the 14 studies is not reported in the abstract. Primary study designs (whether randomized controlled trials or single-arm interventional cohorts) are not specified. Confidence intervals for several outcomes, such as Akkermansia abundance, were wide, and long-term durability or clinical outcomes resulting from these microbiome changes were not measured.
Cited by
- contradicts Ketogenic diets consistently reduce gut microbiome species diversity across multiple scientific studies.