In a recent review published in Nutrients, researchers reviewed preclinical and clinical data to analyze gut microbial alterations in various dietary conditions.

Study: The Beneficial Effects of Dietary Interventions on Gut Microbiota—An Up-to-Date Critical Review and Future Perspectives. Image Credit: LightField Studios/Shutterstock.com

Background

Intermittent fasting (IF), a popular dietary intervention, has been studied for its impact on gut microbial composition and host physiopathological processes.

Studies show that diet constituents modulate the gut microbial community, and the nutrient transformations in microbes deeply influence host metabolism.

This reciprocal association could potentially affect the metabolism of chronic drugs, significantly affecting human health and disease. Dietary interventions for various disorders could be tailored to improve overall health by restoring the gut microbial balance and diversity.

About the review

In the present review, researchers described the impact of diet on the intestinal microbiome by reviewing preclinical and clinical studies published in the PubMed database in English from 2015 to 2023. For preclinical data, only studies published between 2021 and 2023 were included.

Two researchers independently performed data screening, and discrepancies were resolved by consensus. Protocols, studies, and case reports with inaccessible full text were excluded, and eligible records underwent full-text screening. In total, 17 preclinical records and 26 clinical records were analyzed.

Preclinical studies regarding the effects of dietary intervention on the gut microbiota of animals

In six-week-old C57BL/6J mice, high-fat diet (HF) and CR interventions increased Firmicutes, Actinobacteria, Firmicutes: Bacteroidetes ratio, Bifidobacteriaceae, Lactobacillus johnsonii, Bifidobacterium pseudolongum, and Faecalibaculum abundance in the cecum. However, these interventions decreased Bacteroidetes and Parabacteroides counts.

In male Fisher 344 x Brown Norway hybrid F1 rats, time-restricted feeding (TRF) Keto diets reduced fecal Actinobacteria and Patescibacteria counts and increased Verrucomicrobia counts. Western diet TRF (16:8) reduced fecal Bacteroidota, Proteobacteria, and Cyanobacteria counts while increasing Verrucomicrobia counts.

Regular chow diet TRF increased Lactobacillus, Muribaculaceae, Dubosiella, Clostridia, and Faecalibacterium counts. Mother submitted to intermittent fasting (M-IF) feed reduced Lactobacillus intestinalis abundance in mice offspring.

In male Wistar rats, IF reduced Firmicutes: Bacteroidetes ratio and Bacillus velezensis counts, increased Lachnospiraceae and Lactobacillaceae counts, and increased Lactobacillus and Akkermansia muciniphila counts. CR and IF increased Helicobacter, Bacteroidetes, and Firmicutes counts in rainbow trout while reducing Actinobacteria counts in the proximal intestine.

A 16:8 and 24:24 IF intervention increased the abundance of various microorganisms in the feces of allergic mice while reducing Firmicutes counts. Short-term IF reduced Firmicutes, Verrucomicrobia, Lachnospiraceae, Ruminococcaceae, and Ruminiclostridium counts in C57BL/6 mice with induced colitis, while long-term IF reduced Akkermansiaceae and increased Lactobacillaceae counts.

Preclinical studies on gut microbial composition in C57BL/6J mice found it adaptive to dietary modifications. However, the results lacked coherence and homogeneity regarding bacterial strains/group dynamics.

Different types of fasting have other influences on gut microbes, and drawing inferences is challenging due to the study protocols involving various feeding restrictions, durations, and diets. In addition, assessments were performed on several animal models, which could be specifically sensitive to calorie restriction (CR).

Effects of dietary interventions on the human gut microbiota

A randomized controlled trial (RCT) reported that Buchinger fasting for five days increased Proteobacteria and Christensenellaceae counts but reduced Firmicutes: Bacteroides ratio. Water-only fasting reduced Fusobacterium counts and increased homogenous gut microbiota.

Ramadan intermittent fasting increased alpha diversity, Lachnospiraceae, and Ruminococcaceae counts but decreased Bacteroidales. In other studies, Ramadan intermittent fasting reduced Coprococcus, Clostridium_XlV spp., and Lachnospiraceae counts but increased Dorea, Klebsiella, Faecalibacterium, Sutterella, Parabacteroides, Alistipes, Bacteroides, and Firmicutes counts.

Ten days of Buchinger fasting and three months of refeeding reduced Firmicutes counts but increased Bacteroides, Proteobacteria, and Bacteroides. Buchinger fasting followed by a Mediterranean-like diet for hypertensive patients with metabolic syndrome can reduce Bifidobacterium, Coprococcus comes, and Roseburia counts.

In obese postmenopausal women, VLCD for 46 days increases Christensenellaceae counts. In overweight and obese adults, a six-week caloric restriction and weight stabilization diet reduces Akkermansia muciniphila counts.

Dietary restriction can impact the gut microbiota by decreasing proinflammatory cytokines, enhancing short-chain fatty acid (SCFA) production, increasing intestinal barrier integrity, and exhibiting immunomodulatory effects.

Long-term dietary restriction for a year reduced Actinobacteria counts and Firmicutes: Bacteroidetes ratio while increasing Bacteroides, Roseburia, Faecalibacterium, and Clostridium XIVa ratio. No distinct pattern of gut microbiota changes was established; however, health benefits were evident, including reduced risk factors for age-related diseases and increased lifespan.

Based on the review findings, dietary interventions like time-restricted fasting and caloric restriction have been studied for their impact on metabolic health markers and gut microbiota composition. These programs alter the gut environment by changing nutrient availability, energy sources, microbial growth, and SCFA production.

They can decrease inflammation, regulate metabolism, and improve circadian rhythm. However, data is insufficient to establish a typical pattern of gut microbiota changes.

Further research is needed, especially on obese and metabolically compromised patients, to identify long-lasting changes and assess different gut microbiota molecules.