Sponsoring Institution
National Institute of Food and Agriculture
Project Status
Funding Source
Reporting Frequency
Accession No.
Grant No.
Project No.
Proposal No.
Multistate No.
Program Code
Project Start Date
Mar 1, 2023
Project End Date
Feb 28, 2025
Grant Year
Project Director
Millar, C.
Recipient Organization
Performing Department
Non Technical Summary
There are trillion of microbes that live in the instestines (i.e., gut microbes), whichdirectly impact the health of an individual. Recent evidence suggests some gutmicrobes may be able to prevent the development ofdepression (e.g., neuro-inflammation and neurotransmitters). One of the most efficent ways to modulate the gut microbiota is through diet. The long-term goal of this project is to identify nutrients that interact with the gut microbes and influence the processes/pathways relevant to depression. Our preliminary data suggests that intake of dietary fiber and anthocyanins (a dietary antioxidantfound in berries) are associated with reductions in depressive symptoms. Coincidentally, fiber and anthocyanins are metabolized by gut microbes. These gut microbes then produce certain metabolites that may prevent depression (i.e., short chain fatty acids, SCFA). Our objective is to determine if daily consumption ofa whole-food source of dietary fiber and anthocyanins (via freeze-dried blueberry powder) increases certain species of gut microbes, increases gut-derived metabolites relevant to depression, and improves depressive symptoms. This study is an ancillary project to a double-blind, randomized, placebo-controlled clinical trial that consists of a 12-week intervention in older, sedentary adults with depressive symptoms. This study will provide evidence on the utility of fiber- and anthocyanin-rich agricultural foods as a new therapeutic opportunity to improve human health by modulating the gut microbes and metabolites relevant to depression.
Animal Health Component
Research Effort Categories

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
Goals / Objectives
Our major goal is to gather preliminary evidence on the synergistic impact of dietary fiber and anthocyanin intake on the gut microbiota-related pathways/processes relevant to depression utilizing a whole-food approach. We propose an ancillary study to a currently funded (IRB Approval Pro00064749; Co-PI Dr. Millar) randomized, double-blind, placebo-controlled intervention in untreated older adults (≥ 65 y) with depressive symptoms. The aims of this ancillary project are:Objective 1: Determine the impact of daily dietary fiber and anthocyanin (via freeze-dried blueberry powder) intake on microbes that produce gut-derived SCFA in untreated older adults with depressive symptoms by performing a randomized, placebo-controlled, double-blind trial.Objective 2: Determine the effect of daily dietary fiber and anthocyanin intake on fecal SCFA in untreated older adults with depressive symptoms, participating in the clinical trial.Objective 3: Determine the effect of daily dietary fiber and anthocyanin intake on depressive symptom severity in untreated older adults with depressive symptoms, participating in the clinical trial.
Project Methods
This proposal leverages a currently funded individual-level, randomized, double-blind, placebo-controlled, parallel pilot study funded by a National Institute of Aging Roybal Pilot Grant, in 40 sedentary, untreated older adults with depressive symptoms (IRB Approval Pro00064749; Co-PI Dr. Millar).In the partent study, recruited participants will be randomized to consume 48 g/day of freeze-dried blueberry powder (a source anthocyanins and dietary fiber) or 48 g/day of a nutritionally matched placebo powder (devoid of anthocyanins and dietary fiber) mixed in water for 12 weeks. A 48 g dose of the freeze-dried blueberry powder provides ~8 g of dietary fiber and ~600 mg of anthocyanins. The powder will be packaged into individualized packets (24 g/packet), and individuals will be instructed to consume 1 packet in the morning and 1 in the afternoon (i.e., 48 g/day).As an expansion to the parent study, this ancillary study aims to determine the impact of both dietary fiber and anthocyanins on the gut microbiota, gut-derived metabolites, and depressive symptom severity. Thus, particiapnts will be administered a validated questionnaire to evaluate depressive symptoms andasked to providea fecal sampel before and after the intervention period.To evaluate the impact of the dietary fiber and anthocyanin intake on the gut microbiota and SCFA, 3 days prior to baseline or final follow-up visit participants will be asked to collect a fecal sample as is, in a sterile collection tube without any preservation medium that will be provided to participants. Participants will temporarily store the self-collected fecal sample in their own freezer (-17°C), and then transported to the lab at HSL for sample processing and long-term storage until analysis. For analysis of the gut microbiota composition, 300 mg of the fecal sample will be measured and stored at -80°C. For fecal SCFA quantification, 100 mg of the fecal sample will be measured and frozen at -80°C. Once all participants have completed the intervention, the samples will be shipped in bulk for analyses.The abundance of microbes that produce SCFA (e.g., Bifidobacteria, Eubacterium, and Clostridium) will be evaluated by whole genome sequencing (WGS). WGS will be performed in fecal samples before and after the 12 week intervention to obtain a holistic representation of the microbes in the gut and to confirm that the blueberry powder interacts with the gut microbiota WGS was chosen because it enables identification of microbes down to the specific species or strain of bacteria whereas other methods can only identify the genus level. Also, WGS tends to be less biased compared to 16S rRNA sequencing. DNA extraction from fecal samples and whole genome sequence library construction and sequencing, and sequence analysis will be performed by a reputable lab (e.g., theMicrobial Omics Core at the Broad Institute and/ortheHarvard Chan Microbiome Analysis Core).Fecal SCFA will be measured by a reputable lab (e.g., West Coast Metabolomics Center at University of California Davis). Following sample preparation outlined in above, a biphasic extraction will be performed to extract the SCFA from the fecal samples. SCFA will be separated and identified using gas chromatography mass spectrometry. Internal standards and an external curve will be used to calculate the concentration of SCFA) in each sample (acetate, propionate, and butyrate).Depressive symptom severity will be captured with the validated 20-item CES-D questionnaire, which asks participants to self-report the frequency of symptoms commonly experienced in depression. The scores of this assessment range from 0-60 points where higher scores indicate more severe symptoms.Change in depressive symptoms severity will be evaluated throughout the study.