Research Question: ·        The objective of this study is to learn about the number of calories in walnuts and the mechanisms of their health effects. Recruitment Criteria: ·         25-75 years of age ·         Body mass index between 20 and 38 kg/m2 ·         Nonsmokers ·         Not diabetic Requirements: ·         Two 3-week diet periods, separated by a 1-week break. ·         During the two diet periods, participants will come in to the Center for    breakfast and dinner, Monday-Friday. Lunch and weekend meals will be packed for carryout. ·         There will be 4 mornings of testing (one at the beginning and end of each diet period). On two of those mornings (one at the end of each diet period) you will be at the Center for approximately 4.5 hours. ·         There will be a total of 6 blood draws. ·         Fecal and urine samples will be collected for 7 days during each diet period. ·         Volunteers will be compensated. Information Meetings: ·         If you are interested in participating, you must attend an information meeting to learn of the details of the study. The meetings will be held at the following dates and times:   o   Monday 4/15/2013 at 5:00PM o   Tuesday 4/16/2013  at 12:00PM