In conclusion, monomeric and oligomeric flavan-3-ols displayed a very selective antimicrobial activity, with high inhibitory activity against those members of intestinal microbiota that rely on anaerobic electron transfer chains but limited or no activity against facultative anaerobes including lactic acid bacteria or Enterobacteriaceae. Enzyme inhibition by flavan-3-ols increased with the number of hydroxy groups in the molecule located on the B ring of the monomer and with the number of gallate moieties attached. The length of the oligomer does not seem to play a role in the antimicrobial activity of grape seed procyanidins but has an influence on their enzyme inhibitory activity, with higher DP being more effective. Grape seed serves as an economical and valuable source of bioactive procyanidins which can exert health effects by modulation of gut microbiota and altering the digestibility of food. Overall, an improved understanding on how procyanidins interact with human digestive enzymes and specific groups of intestinal microbes will further our understanding of their role in a diet containing plant foods that are rich in dietary fibre and plant phytochemicals. The comprehensive assessment of the individual and joint impact of procyanidins, other bioactive phytochemicals and dietary fibre on gut microbiota, however, remains subject to future studies.