Enzymes are bio-catalysts that alter the speed of the reaction. In the body, they quicken up the process of breaking down nutrients into smaller particles which can be absorbed into the bloodstream. For example, putting a sample of protein in water will take about 50 years (I think) to break down into amino acids. However, adding proteases reduces that to a few hours.
Hope that helps...
enzymes lower down the activation energy of the reaction i.e. the maximum energy required for the reaction to take place. so the reaction takes lesser time