Table 1. Human and animal studies assessing the effect of meat product consumption on the composition of gut microbiota.

Citation	Study design	Intervention	Trial duration	Participants	Effect on the gut microbiota
Kohnert et al. (2021)	Randomized, controlled trial	Meat-rich diet; >150 g of meat/d Strict vegan diet	4 wk	53 Healthy adults 18–60 yr	In meat-rich group No change in alpha- or beta-diversity Coprococcus ↓ Roseburia ↑ Faecalibacterium ↑ Blautia ↑
Russell et al. (2011)	Randomized, crossover trial	Maintenance diet (M); 13% protein and 50% carbohydrates High-protein and moderate-carbohydrate diet (HPMC); 28% protein and 35% carbohydrate High-protein and low-carbohydrate (HPLC); 29% protein and 5% carbohydrate	4 wk	17 Healthy males 21–74 yr Body mass index (BMI) 27.88–48.48	In HPLC group Roseburia/Eubacterium rectale ↓ Bacteroides spp. ↓
Foerster et al. (2014)	Randomized, crossover trial	Low-meat high-fiber period; whole grain products, 40 g of fiber/d High-meat low-fiber period; 200 g of red meat/d	3 wk	20 Healthy adults 20–60 yr	In high-meat low-fiber period Clostridium sp. ↓
Hentges et al. (1977)	Crossover trial	High-beef diet; 380 g of beef/d Meatless diet; 360 g milk; 150 g egg; 145 g cheese; 100 g peas	4 wk	10 Healthy males	In high-beef diet Genus Bacteroides ↑ Species Bacteroides fragilis ↑ Bifidobacterium adolescentis ↓
Zhao et al. (2019b)	Crossover, controlled trial	Beef-based diet Chicken-based diet	2 wk	45 Healthy males 18–27 yr	In beef-based diet Lachnospira ↓ Lachnospiraceae NK4A136 group ↓ Ruminococcus 2 ↓
Dhakal et al. (2022)	Randomized, crossover, controlled trial	Pork group; 156 g pork/d Chicken group; 156 g chicken/d	10 d	50 Healthy older adults 66.44±7.44 yr BMI 29.8±5.59	In both groups No change in alpha- or beta-diversity Phylum Bacteriodetes ↓ Family Bacteriodaceae ↓ Christencellaceae ↑ In pork group Ruminiclostridium 5 ↑ In chicken group Roseburia ↓
Shi et al. (2021)	Cross-sectional study	Not applicable (NA)	NA	40 Healthy males 18–30 yr; chicken-eaters (n=20) and pork-eaters (n=20)	In pork-eater group Chao and Shannon index ↓ Phylum Firmicutes ↑ Bacteroidetes ↓ Genus Clostridiales, Bacteroides, Firmicutes, Lachnospiraceae, Faecalibacterium, Roseburia, Ruminococcus 2, and Blautia ↑ In chicken-eater group Phylum Firmicutes ↓ Bacteroidetes ↑ Genus Prevotellaceae, Prevotella 9, Bacteroidales, Dialister, Prevotella 2, Ruminococcaceae UCG 002, Lactobacillus, and Olsenella ↑
Sinha et al. (2021)	Dietary intervention (participants were blinded to which group they were assigned)	First phase (2 wk): conventional processed meats (Diet A) Second phase (2 wk): poultry (i.e., chicken and turkey) (Diet B) Third phase (2 wk): Group 1) conventional processed meat supplemented with natural phytochemical compounds (Diet C) Group 2) low-nitrite processed meat supplemented with phytochemical compounds (Diet D) Final phase (1 wk): nitrate-enriched water with diet A, B, C, or D	7 wk	63 Healthy volunteers (participants of each sex were randomly assigned to one of the two experimental groups) (ages 18–70, in good health, with a BMI between 18 and 25 kg/m2)	NA
Gao et al. (2021)	Randomized controlled-feeding trial	Control group: restricted from fried meat intake (n=58) Fried meat group: fried meat four times per week (n=59)	4 wk	117 Participants, (18–35 yr old, BMI>24 kg/m2, and consumption of fried food more than one time per wk)	Family Lachnospiraceae ↓ Genus Flavonifractor ↓ Dialister ↑ Dorea ↑ Veillonella ↑
Thøgersen et al. (2018)	Chow, Conventional frankfurter sausage	Inulin-enriched frankfurter sausage	4 wk	30 Healthy Sprague-Dawley rats	Phylum Actinobacteria ↑ Family unclassified Lachnospiraceae ↑ Erysipelotrichaceae ↑ Genus Bifidobacterium ↑ Species Bacteroides uniformis ↑
Thøgersen et al. (2020)	Control sausage	Sausage+inulin and calcium Sausage+inulin Sausage+calcium	4 wk	48 Healthy Sprague-Dawley rats	Phylum Firmicutes ↑ (Sausage+calcium, Sausage+inulin and calcium) Bacteroidetes ↓ (Sausage+calcium, Sausage+inulin and calcium) Proteobacteria, Cyanobacteria ↓ (Sausage+inulin and calcium) Deferribacteres ↑ (Sausage+calcium) Actinobacteria ↑ (Sausage+inulin and calcium) Genus Muribaculaceae, uncultivated Ruminococcaceae ↑ (Sausage+Inulin) Clostridium 6, Staphylococcus, uncultivated Ruminococcaceae (PAC000661) ↑ (Sausage+calcium) uncultivated genus (PAC002482), Parabacteroides, Alistipes, Clostridium, unclassified Peptostreptococcaceae ↓ (Sausage+calcium) Bifidobacterium, Staphylococcus, Blautia, uncultivated Ruminococcaceae (PAC000661), uncultivated Erysipelotrichaceae (CCMM), Faecalibaculum ↑ (Sausage+inulin and calcium) Bacteroides, Parabacteroides, Alistipes, Clostridium, Dorea, uncultivated Bacteroidetes (PAC002482), Muribaculaceae (PAC001472), Lachnospiraceae (KE159600), unclassified Firmicutes ↓ (Sausage+inulin and calcium) Lactobacillus ↑ (q=0.63; Sausage+calcium, Sausage+inulin and calcium)
Fernandez et al. (2020)	Control diet (universal feed)	Acorn-fed Iberian commercial ham	2 wk	20 Male Fischer 344 rats (5 wk old) (ulcerative colitis was induced with dextran sulfate sodium in drinking water ad libitum for 1 wk)	Phylum Bacteroidetes, Actinobacteria, Proteobacteria ↑ Firmicutes, Synergistetes, Deferribacteres ↓ Family Coriobacteriaceae, Bacteroidaceae, Porphyromonadaceae, Rikenellaceae, Desulfovibrionaceae, Sutterellaceae, Staphylococcaceae, Enterococcaceae, Clostridiaceae Family XIII, Eubacteriaceae, Acidaminococcaceae, Erysipelotrichaceae, Enterobacteriaceae ↑ Marinifilaceae, Prevotellaceae, Sphingobacteriaceae, Ruminococcaceae, Lachnospiraceae, Clostridiaceae, Veillonellaceae, Lactobacillaceae, Cohaesibacteriaceae ↓ Genus Bacteroides, Butyricimonas, Parabacteroides, Alistipes, Staphylococcus, Enterococcus, Blautia, Dorea, Absiella, Phascolarctobacterium, Parasutterella, Bilophila ↑ Prevotella, Mucispirillum, Lactobacillus, Clostridium, Lachnoanaerobaculum, Ruminococcus, Oscillibacter, Desulfovibrio ↓