The specific aims of the Grain Study are to determine if exposure to different types of grain products, over a period of 6 weeks, changes liking and acceptability and to determine if the gut microbiota, bacterial fermentation products, or gastrointestinal function changes with consumption of whole grains or refined grains.

Subjects will be recruited in accordance with inclusion and exclusion criteria listed below. Subjects will be assigned to one of two different grain product 'exposure' groups - Group 1 will receive predominantly Whole Grain (WG) products and Group 2 will receive predominantly Refined Grain (RG) products (ratio of WG to RG assignment will be 2:1). For a 6-week exposure period, subjects will receive weekly market baskets of grain products consisting of breakfast cereals, breads, snack items, and side dishes with the target of providing whole grains at a level of 85% of grain intake for the WG group (this exceeds the current Dietary Guideline recommendation of 50%) and 15% for the RG group (this is the current estimated intake for U.S. adults). Before and after grain exposure, subjects will rate the acceptability and liking of numerous grain products. To accomplish this, subjects will participate in sensory evaluation tests using these products, and they will provide information using validated questionnaires and take implicit association tests. During the 6-week study period, subjects will record use of the market basket grain products, and provide subjective scores for taste, convenience, nutrition, and general liking. The quality of the total dietary intake will be assessed using unannounced 24-h recalls. Biological samples will also be collected from subjects. Blood and urine samples will be collected to evaluate risk factors of chronic disease, and biomarkers of whole grain intake, fruits and vegetables. Saliva and fecal samples will be collected to measure changes in gut microbiota and to measure metabolites of bacterial fermentation. Breath hydrogen tests will be conducted to measure bacterial fermentation. Two weeks after the end of the intervention period, subjects will participate in a nominal group session to identify significant barriers and facilitators to inclusion of grain products into their diets.

Inclusion Criteria:

• 20-45 years of age
• male or female
• consumers of 1 or fewer whole grain products per day

Exclusion Criteria:

• Type I or II Diabetes or glucose intolerance
• Preference for whole grains
• Do not cook at home
• Pregnant or planning to be pregnant
• Smoking
• Chronic inflammatory bowel disease
• colorectal cancer
• Celiac disease or gluten sensitivity
• Crohn's disease
• Regular use of colonics and/or laxatives
• body weight change of >3% in last 6 months
• use of antibiotics, appetite suppressants, mood altering medications, and regular tobacco use.