TABLE 3.
Summary of the human studies investigating the effects of fasting on gut microbiota alterations.
| References | Fasting model | Study type/duration | Study population | Results |
| Su et al. (49) | 1 month of intermittent fasting | Longitudinal physiologic data in 2 cohorts, sampled in 2 different years | Healthy non-obese young and middle-aged men | Ramadan-associated intermittent fasting increased microbiome diversity and was specifically associated with upregulation of the Clostridiales order–derived Lachnospiraceae |
| Mohammadzadeh et al. (39) | Hour time restricted feeding intervention (8-h feeding window/16-h fasting window) | Before/after the cross-sectional study | Healthy adult volunteers (n = 30) | Butyrate significantly increases, the gut Bacteroides and Firmicutes increased by 21 and 13% after Ramadan. |
| Gabel et al. (40) | A daily 8-h time restricted feeding (8-h feeding window/16-h fasting window) for 12 weeks | Pilot study/12 weeks | Adults with obesity (n = 14) | Gut microbiota phylogenetic diversity remained unchanged. |
| Maifeld et al. (50) | Ramadan fasting | Clinical trial | Healthy subjects (n = 30) | Fasting alters the gut microbiome, impacting bacterial taxa and gene modules associated with short-chain fatty acid production. |
| Maifeld et al. (50) | 5-days with a daily nutritional energy intake of 300–350 kcal/day, derived from vegetable juices and vegetable broth, followed by a modified Dietary Approach to Stop Hypertension diet | Randomized-controlled bi-centric/12 weeks | Patients with Metabolic Syndrome (n = 32–31) | Fasting alters the gut microbiome, impacting bacterial taxa and gene modules associated with short-chain fatty acid production. |
| Lilja et al. (52) | Buchinger fasting: 250 kcal/day for 5 days | RCT | 154 healthy adults | ↑ Distribution of Proteobacteria, ↓ Firmicutes/Bacteroidetes ratio fasting mimetic |
| Guo et al. (41) | “Two-day” modified IF | Clinical trial, 8 weeks | Adults with Metabolic Syndrome (n = 39) | Changes in gut microbiota communities, increase the production of short-chain fatty acids, and decrease the circulating levels of lipopolysaccharides. |
| He et al. (53) | Water-only fast or juice fast for 7 days | Intervention pre-post design | 16 healthy individuals, age: 18–40 years | Water-only fasting changed the bacterial community, ↑ more homogenous gut microbiomes, ↓ Fusobacterium. ↓ Colorectal cancer |
| Ali et al. (38) | Ramadan fasting | Cohort | Healthy adult participants (n = 34) | ↑ Klebsiella, Faecalibacterium, Sutterella, Parabacteroides, and Alistipes ↓ Coprococcus, Clostridium_XlV, and Lachnospiracea |
| Balogh et al. (55) | Buchinger fasting protocol followed by DASH diet | RCT/5 days | Control (n = 36), fasting (n = 35) | ↑ Clostridial Firmicutes ↓ Butyrate producers |
| Ozkul et al. (37) | Ramadan fasting | Pilot study/29 days | Healthy adult participants (n = 9) | Butyricicoccus, Bacteroides, Faecalibacterium, Roseburia, Allobaculum, Eubacterium, Dialister, and Erysipelotrichi were significantly enriched genera after the end of Ramadan fasting. |
| Mesnage et al. (56) | Buchinger fasting (daily energy intake of about 250 kcal and an enema every 2 days | Clinical study/10-day | Healthy men (n = 15) | Decrease in the abundance of Lachnospiraceae and Ruminococcaceae increase in Bacteroidetes and Proteobacteria (Escherichia coli and Bilophila wadsworthia). |
| Remely et al. (57) | A fasting program with laxative treatment for 1 week followed by a 6-week intervention with a probiotic formula | One week | Overweight people (n = 13) | Fasting group had higher abundance of Faecalibacterium prausnitzii, Akkermansia, and Bifidobacteri |