Aims Investigation of intestinal bacterial groups involved in phytate degradation and the impact of diets with different phytate contents on phytase activity. Methods and Results Faecal samples of adults on conventional (n=8) or vegetarian (n=8) diets and breastfed infants (n=6) were used as an inoculum for modified media supplemented with phytate. Populations of Gram-positive anaerobes (GPA), lactic acid bacteria (LAB), Proteobacteria-Bacteroides (P-B), coliforms and anaerobes were studied. The PCR-DGGE analysis revealed a random distribution of DGGE profiles in the dendrograms of GPA, P-B and coliforms, and a partially diet-specific distribution in the DGGE dendrograms of LAB and anaerobes. The degradation of phytic acid (PA) was determined with HPLC method in supernatants of the cultures. Regardless of the diet, the Gram-positive anaerobes and LAB displayed the lowest ability to degrade phytate, whereas the coliforms and P-B cultures produced higher amounts of intermediate myo-inositol phosphates. Bacterial populations grown in a nonselective medium were the most effective ones in phytate degradation. It was the vegetarians' microbiota that particularly degraded up to 100% phytate to myo-inositol phosphate products lower than InsP3. Conclusions A diet rich in phytate increases the potential of intestinal microbiota to degrade phytate. The co-operation of aerobic and anaerobic bacteria is essential for the complete phytate degradation. Significance and Impact of the Study This study provides insights on the effect of diet on specific metabolic activity of human intestinal microbiota.