The objective of this study is to measure the energy value of walnuts in the human diet and study molecular mechanisms that may help explain the beneficial health effects of walnuts. The hypothesis is that there will be less metabolizable energy in walnuts due to decreased fat digestibility.

Previous studies have demonstrated that nut consumption imparts a variety of health benefits, including reduction of cardiovascular disease and improved satiety. The aim of this study is to determine the energy value of walnuts in the human diet and to probe mechanisms by which walnuts impart health benefits. The metabolizable energy value of walnuts will be calculated based on the chemical composition and energy content of the consumed diet and excreta. This will provide a better estimate of the energy value of walnuts than simply calculating energy value based on Atwater factors. In addition to determining the energy value of walnuts, we will evaluate the effects of walnut-rich diets on plasma phytonutrient levels and on gene expression changes to determine what protective mechanisms are activated by walnut consumption.

Inclusion Criteria:

• Age 25 to 65 years at beginning of study
• Body mass index between 20 and 38 kg/m2
• Fasting glucose < 126 mg/dl
• Blood pressure < 160/100 (controlled with certain medications)
• Fasting total blood cholesterol < 280 mg/dl
• Fasting triglycerides < 300 mg/dl

Exclusion Criteria:

• Presence of kidney disease, liver disease, gout, hyperthyroidism, untreated or unstable hypothyroidism, certain cancers, gastrointestinal disease, pancreatic disease, other metabolic diseases, or malabsorption syndromes
• Women who have given birth during the previous 12 months
• Pregnant women or women who plan to become pregnant or become pregnant during the study
• Lactating women
• Type 2 diabetes requiring the use of oral antidiabetic agents or insulin
• History of bariatric or certain other surgeries related to weight control
• Smokers or other tobacco users (during 6 months prior to the start of the study)
• Antibiotic use during the intervention or for 3 weeks prior to any intervention period
• History of eating disorders or other dietary patterns which are not consistent with the dietary intervention (e.g., vegetarians, very low fat diets, high protein diets)
• Volunteers who have lost 10% of body weight within the last 12 months
• Known (self-reported) allergy or adverse reaction to walnuts or other nuts
• Unable or unwilling to give informed consent or communicate with study staff
• Self-report of alcohol or substance abuse within the past 12 months and/or current acute treatment or rehabilitation program for these problems (long-term participation in Alcoholics Anonymous is not an exclusion)
• Other medical, psychiatric, or behavioral factors that in the judgment of the Principal Investigator may interfere with study participation or the ability to follow the intervention protocol