In a recent review published in Nutrients, researchers assessed preclinical and clinical data to analyze gut microbial changes in different nutritional conditions.
Study: The beneficial effects of nutritional interventions on the gut microbiota: a current critical review and future perspectives. Image credits: LightField Studios/Shutterstock.com
Background
Intermittent fasting (IF), a popular nutritional intervention, has been investigated for its impact on intestinal microbial composition and host physiopathological processes.
Studies show that dietary components modulate the gut microbial community, and nutrient transformations in microbes have a major impact on host metabolism.
This mutual association could potentially influence chronic drug metabolism, significantly affecting human health and disease. Dietary interventions for various conditions can be tailored to improve overall health by restoring microbial balance and diversity in the gut.
About the review
In the current review, researchers described the impact of diet on the gut microbiome by assessing preclinical and clinical studies published in the PubMed database in English between 2015 and 2023. For preclinical data, only studies published between 2021 and 2023 were included.
Two investigators independently performed data screening and discrepancies were resolved by consensus. Protocols, studies, and case reports with inaccessible full text were excluded and eligible records were screened in full text. A total of 17 preclinical and 26 clinical files were analyzed.
Preclinical studies on the effects of nutritional interventions on the intestinal 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 pseudolongumAnd Faecalibaculum abundance in the cecum. However, these interventions have declined Bacteroidetes And Parabacteroids counts.
In male Fisher 344 x Brown Norway hybrid F1 rats, time-restricted feeding (TRF) keto diets reduced fecal Actinobacteria And Patescibacteria counts and magnifies Verrucomicrobia counts. Western diet TRF (16:8) reduced bowel movements Bacterioidota, ProteobacteriaAnd Cyanobacteria counts as it increases Verrucomicrobia counts.
Regular chow diet TRF increased Lactobacillus, Muribaculaceae, Dubosiella, Clostridia, And Faecalibacterium counts. Mother subjected to intermittent fasting (M-IF) feeding reduced Lactobacillus intestinalis abundance of mouse offspring.
In male Wistar rats, IF was reduced Firmicutes: Bacteroidetes proportions Bacillus veezensis counts, increased Lachnospiraceae And Lactobacillaceae counts and has increased Lactobacillus And Akkermansia muciniphila counts. CR and IF increased Helicobacter, BacteroidetesAnd Firmicutes counts in rainbow trout while it is reduced Actinobacteria counts in the proximal intestine.
A 16:8 and 24:24 IF intervention increased the abundance of different microorganisms in the feces of allergic mice, while the Firmicutes counts. IF reduced in the short term Firmicutes, Verrucomicrobia, Lachnospiraceae, RuminococcaceaeAnd Ruminiclostridium counts in C57BL/6 mice with induced colitis, while IF decreased in the long term Akkermansiaceae and increased Lactobacillaceae counts.
Preclinical studies of gut microbial composition in C57BL/6J mice have shown adaptability to dietary changes. However, the results lacked coherence and homogeneity with regard to bacterial strains/group dynamics.
Different types of fasting have different influences on gut microbes, and drawing conclusions is challenging due to the study protocols with different dietary restrictions, durations, and diets. In addition, assessments have been performed on several animal models, which could be specifically sensitive to calorie restriction (CR).
Effects of nutritional interventions on the human gut microbiota
A randomized controlled trial (RCT) reported that Buchinger’s fasting increased for five days Proteobacteria And Christensenellaceae counts but has been reduced Firmicutes: Bacteroides ratio. Water-only fasting is reduced Fusobacterium numbers and increased homogeneous intestinal microbiota.
Intermittent fasting during Ramadan increased alpha diversity, LachnospiraceaeAnd Ruminococcaceae counts, but has decreased Bacteroidales. In other studies, intermittent fasting during Ramadan was reduced Coprococcus, Clostridium_XlV spp., and Lachnospiraceae counts, but has increased Dorea, Klebsiella, Faecalibacterium, Sutterella, Parabacteroids, Alistipes, Bacteroids, And Firmicutes counts.
Ten days of Buchinger fasting and three months of refeeding shortening Firmicutes counts, but has increased Bacteroids, ProteobacteriaAnd Bacteroids. Buchinger fasting followed by a Mediterranean diet can reduce symptoms in hypertensive patients with metabolic syndrome Bifidobacterium, Coprococcus comes, And Rozeburia counts.
In obese postmenopausal women, VLCD increases over 46 days Christensenellaceae counts. In overweight and obese adults, a six-week calorie restriction and weight stabilization diet reduces weight loss Akkermansia muciniphila counts.
Dietary restriction may impact the gut microbiota by reducing pro-inflammatory cytokines, enhancing short-chain fatty acid (SCFA) production, increasing intestinal barrier integrity, and exhibiting immunomodulatory effects.
Long-term dietary restriction reduced for one year Actinobacteria counts and Firmicutes: Bacteroidetes ratio as it increases Bacteroids, Rozeburia, FaecalibacteriumAnd Clostridium XIVa ratio. No clear pattern of changes in the gut microbiota was identified; however, the health benefits were clear, including reduced risk factors for age-related diseases and increased longevity.
Based on the study results, nutritional interventions such as time-restricted fasting and calorie restriction were examined for their impact on metabolic health markers and the composition of the gut microbiota. These programs alter the intestinal environment by altering nutrient availability, energy sources, microbial growth, and SCFA production.
They can reduce inflammation, regulate metabolism and improve circadian rhythm. However, there are insufficient data to establish a typical pattern of changes in the gut microbiota.
Further research is needed, especially in obese and metabolically compromised patients, to identify long-term changes and assess different gut microbiota molecules.