Location: Food Components and Health Laboratory
Project Number: 8040-51530-010-13-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 15, 2014
End Date: Sep 14, 2019
To investigate the effect of dietary changes in humans on their microbiota, with focus on colonic changes.
The approach for this project will be to feed human volunteers controlled diets and use microbial analysis of fecal samples as a surrogate marker for colonic microbiota composition. Human volunteers will be fed a variety of diets that may include, among other dietary manipulations, diets that are specifically designed to ask questions about the effect of tree nuts, grains, and polyphenols on microbial composition. Tree nuts will include walnuts and almonds, and may include other tree nuts. Research with walnuts and almonds is specifically related to ARS Project #1235-51530-010-00D titled “Metabolism and Molecular Targets of Macro and Micro Food Components in the Development and Management of Obesity and Chronic Diseases.” In this project, objective #1 is to “Determine the energy content of specific foods in the context of a mixed diet, and the absorption, metabolism and impact on biomarkers for health promotion of these foods or their macro and micro components”. As a part of this objective, two studies are planned, one with walnuts and one with almonds. Fecal microbiota analysis is included as an outcome in these studies since microbiota in the gastrointestinal tract is modifiable by diet. These microbes have been found responsive to a variety of dietary manipulations, albeit many of these dietary interventions include foods that are typically well-digested such as dietary carbohydrate and fat. Nuts are not well-digested so it’s expected that consumption of poorly digested foods, such as nuts, would provide different substrates to the gut microbiota and thus impact their composition. These two studies are designed as controlled-feeding (all food provided and measured to the nearest 1 g) during the entirety of each treatment period), randomized crossover trials. The volunteer recruitment, feeding, and sample collection will take place at the Beltsville Human Nutrition Research Center. For the study of walnuts, the two treatments will be 0 g/day and 42 g/day of whole and chopped walnuts fed as part of a weight maintaining controlled diet for 21 days. For the study of almonds, treatments will be the following incorporated daily into a controlled diet: 1) No almonds, 2) 42 g whole raw almonds, 3) 42 g whole roasted almonds, 4) 42 g slivered raw almonds, 5) 42 g almond butter. Meals will be prepared using traditional American foods. For microbiota analysis form both of these studies, fecal samples will be collected on the first and last day of each 21-day feeding period. For the microbiota analysis, all samples will be delivered on ice, usually within 4 hrs of defecation. Samples will be processed by kneading in a plastic bag immediately upon arrival in the laboratory and stored at -80'C until shipped on dry ice, overnight to the University of Illinois where microbiota analyses will occur. Approximately 252 samples will be collected from these studies. Methods of analysis will include state-of-the-science sequencing techniques and may include other well-established quantitative and qualitative measures such as denaturing gradient gel electrophoresis, quantitative polymerase chain reaction, and fluorescence in situ hybridization.