TABLE 3.
Human trials investigating the effect of nut consumption on the gut microbiome1
| Study (ref) | Study design | Subjects | Treatment | Duration | Related endpoints | Results |
|---|---|---|---|---|---|---|
| Liu et al. (113) | 3-arm parallel | Healthy men and women (n = 46) | 8 g FOSs/d (no nuts), 10 g almond skins/d, 56 g almonds/d | 6 wk | Fecal water, pH, bacteria enumeration, enzyme activity | No changes in fecal water or pH |
| All groups increased Bifidobacterium spp., Lactobacillus spp., with no significant differences between groups | ||||||
| Almond skin and FOSs increased β-galactosidase activity | ||||||
| β-Glucuronidase activity was decreased after FOSs and almond skin | ||||||
| All groups showed decreased nitroreductase activity | ||||||
| Ukhanova et al. (112) | Randomized, crossover feeding trial | Healthy men and women (n = 18; almond) (n = 16; pistachio) | No nuts, 42.5 g almonds or pistachios/d, 85 g almonds or pistachios/d with base typical low-fiber American diet | 18 d | Diversity, OTUs | Pistachios decreased Lactobacillus |
| No significant change in bifidobacteria with either nut | ||||||
| Both nuts decreased OTUs closest to Firmicutes bacterium and Clostridium spp. | ||||||
| Both nuts increased butyrate producers | ||||||
| Burns et al. (114) | Randomized crossover trial | Parent-child pairs (n = 28) | No nuts, 42.5 g almonds or almond butter/d (parents), 14 g almonds or almond butter/d (children) | 3 wk | Diversity, OTUs | No significant differences in diversityNo significant differences in OTUs |
| Holscher et al. (115) | Randomized, crossover feeding trial | Healthy men and women (n = 18) | No nuts, 42 g whole almonds/d, 42 g whole, roasted almonds/d, 42 g roasted chopped almonds/d, 42 g almond butter/d | 3 wk | Diversity, OTUs | No significant differences in diversityWhole almonds significantly increased DialisterWhole roasted almonds significantly increased LachnospiraChopped almonds significantly increased Lachnospira, Roseburia, and OscillospiraNo significant differences between almond butter and controlSignificantly more fungal OTUs after whole almonds |
| Holscher et al. (116) | Randomized, crossover feeding trial | Healthy men and women (n = 18) | No nuts or 42 g walnuts/d | 3 wk | Diversity, OTUs, primary and secondary bile acids | No significant differences in diversityWalnuts significantly increased Firmicutes and decreased ActinobacteriaWalnuts significantly increased Faecalibacterium, Clostridium, Roseburia, and DialisterNo significant changes in primary bile acidsWalnuts significantly reduced secondary bile acids |
| Bamberger et al. (117) | Randomized crossover trial | Healthy men and women (n = 135) | No nuts or 43 g walnuts/d | 8 wk | Diversity, OTUs | Significant dissimilarities between walnut and controlWalnuts significantly increased Ruminococcaceae and Bifidobacteria and decreased Clostridium spp. |
1
PubMed search terms included the following: “nuts AND microbiome”, “almonds AND microbiome”, “Brazil nuts AND microbiome”, “cashews AND microbiome”, “hazelnuts AND microbiome”, “macadamia nuts AND microbiome”, “pecans AND microbiome”, “pine nuts AND microbiome”, “pistachios AND microbiome”, “walnuts AND microbiome”. Studies were included based on the inclusion criteria of human clinical trials with gut-microbiome outcomes, such as diversity. FOS, fructo-oligosaccharide; OTU, operational taxonomic unit; ref, reference.