Inclusion Criteria:  Diagnosis of acute lymphocytic or myelocytic leukemia or lymphoma at the at Children's Hospital Colorado or the University of Colorado Hospital Diagnosis of first time or first recurrent CDI as defined by clinical criteria within the past 7 days Informed consent and assent obtained and signed. At least 9 years old. 40th to 100th percentiles of saturated fat intake and below the 50th percentile for fiber intake based on a food frequency questionnaire. Ability to comply with study procedures for the entire length of the study.