The purpose of the study is to examine how a dietary fiber affects metabolism in healthy overweight and obese adults. The fiber will be added to foods that participants will consume for two, three-week periods. The fiber will be given in two doses -- 15 g per day during one period, and 30 g per day in the other. In another three-week period, they will consume the same foods, but with no fiber added. Major outcomes will include fermentability of the fiber, as assessed by measurement of breath hydrogen, as well as shifts in fecal bacteria. The caloric value of the fiber will be determined and metabolic measures related to blood glucose control and inflammation will also be taken.

Inclusion Criteria:

• Body mass index from 25 to 35 kg/m2.
• Willing to consume study foods and comply with dietary exclusions and specimen collection

Exclusion Criteria:

• Pregnancy
• Diabetes
• Gastrointestinal disease
• Regular use of pre- or probiotics
• Recent use of antibiotics
• High intake of dietary fiber