Soluble (SOL) and insoluble (INSOL) NSP may influence gut bacteria populations, reflecting changes in fermentable material in the gut. Effects of purified (SOL, guar gum; INSOL, cellulose) NSP fractions on ileal bacteria populations and energy digestibility were studied. Pigs surgically fitted with an ileal T-cannula were fed four experimental diets (14% cornstarch basal [control]; 7% SOL +7% INSOL NSP [SOL + INSOL]). Diets were fed for 13 d, ileal digesta was collected under CO2, and bacteria were cultured on selective bacteria counts except for Bifidobacteria. Compared to control, addition of soluble and insoluble NSP reduced energy digestibility from 73 to 39% in the ileum, but only marginally across the total tract. Increasing dietary purified soluble and insoluble NSP reduces nutrient digestibility and subsequently, increases the amount of fermentable dry matter in the small intestine, thereby providing further substrate fro ileal bacteria proliferation in grower pigs.