Almonds　and　almond　skins　are　rich　in　fiber　and　other　components　that　have　potential　prebiotic　properties.　In　this　study　we　investigated　the　prebiotic　effects　of　almond　and　almond　skin　intake　in　healthy　humans.　A　total　of　48　healthy　adult　volunteers　consumed　a　daily　dose　of　roasted　almonds　(56g),　almond　skins　(10g),　or　commercial　fructooligosaccharides　(8g)　(as　positive　control)　for　6　weeks.　Fecal　samples　were　collected　at　defined　time　points　and　analyzed　for　microbiota　composition　and　selected　indicators　of　microbial　activity.　Different　strains　of　intestinal　bacteria　had　varying　degrees　of　growth　sensitivity　to　almonds　or　almond　skins.　Significant　increases　in　the　populations　of　Bifidobacterium　spp.　and　Lactobacillus　spp.　were　observed　in　fecal　samples　as　a　consequence　of　almond　or　almond　skin　supplementation.　However,　the　populations　of　Escherichia　coli　did　not　change　significantly,　while　the　growth　of　the　pathogen　Clostridum　perfringens　was　significantly　repressed.　Modification　of　the　intestinal　microbiota　composition　induced　changes　in　bacterial　enzyme　activities,　specifically　a　significant　increase　in　fecal　β-galactosidase　activity　and　decreases　in　fecal　β-glucuronidase,　nitroreductase　and　azoreductase　activities.　Our　observations　suggest　that　almond　and　almond　skin　ingestion　may　lead　to　an　improvement　in　the　intestinal　microbiota　profile　and　a　modification　of　the　intestinal　bacterial　activities,　which　would　induce　the　promotion　of　health　beneficial　factors　and　the　inhibition　of　harmful　factors.　Thus　we　believe　that　almonds　and　almond　skins　possess　potential　prebiotic　properties.©　2013　Elsevier　Ltd.