Recipient Organization
OHIO STATE UNIVERSITY
1680 MADISON AVENUE
WOOSTER,OH 44691
Performing Department
(N/A)
Non Technical Summary
Consuming walnut as part of a healthy diet has been associated with higher cognitive function in adults. This project will test the cause-effect relationship between walnut consumption and cognition in adults.
Animal Health Component
70%
Research Effort Categories
Basic
30%
Applied
70%
Developmental
0%
Goals / Objectives
OBJECTIVE 1: To measure the impact of walnuts on postprandial cognitive function in adults who report subjective cognitive complaints.Primary Hypothesis 1A: The primary hypothesis of this proposal, and on which power was calculated, is a walnut meal will support higher postprandial cognitive function compared to a meal without walnuts. Predetermined covariates, including pre-meal cognitive scores, age, sex, obesity, and education level, will be adjusted to approve accuracy and precision in evaluating the influence of walnuts on postprandial cognitive function. A mixed model will be used for data analysis on intent-to-treat basis. Hypothesis 1B: Our secondary hypothesis is that 7 days of consuming a walnut snack (56 g/d) will result in better baseline (under fasting condition) cognitive function than baseline cognitive performance after 7 days of consuming a control snack. Hypothesis 1C: Using a biomarker of walnut intake, e.g., sum of ALA + LA [53], a higher magnitude of change of plasma sum of ALA+LA is correlated to better cognitive function (baseline test.)OBJECTIVE 2: To assess the effect of daily walnut consumption on the gut-brain axis in relationship to cognitive function.Hypothesis 2A: Daily walnut consumption (56 g walnuts per day) for seven days will reduce endotoxemia, a marker of intestinal permeability; and Hypothesis 2B: Seven days of walnut consumption will increase b-diversity and alter microbiota taxa in the intestinal tract. Hypothesis 2C: The changes of endotoxemia and microbiota composition in response to walnut supplementation will track with preservation of post-prandial cognitive function.
Project Methods
We will also screen for people with BMI>30 kg/m2. Therefore, we will accrue participants (ages 40-75) who subjectively report cognitive impairment and who are also obese but who are not diagnosed with dementia. Roughly three days prior to each clinical visit, a clinical coordinator will phone study participants to remind them of preparation instructions for their upcoming visit. Participants will arrive at the OSU Clinical Nutrition Research Center (ideally between 7:00 am and 9:00 am) after a 12-hr fast then will be settled into a quiet room for the measurement of vital signs, blood pressure, and body weight.For the day prior to each postprandial visit (visits 3 and 5), participants will be provided foods for all meals and snacks for the full day based on estimated energy needs for one day using BMI, age, sex and physical activity level for energy estimates[80]. As described in prior research, controlled feeding of prior-day meals (e.g., 30% fat, 20% protein and 50% complex carbohydrates with low added sugars[61, 62]) minimizes variation for postprandial measurements[23, 61, 62].On the day of the meal challenge, participants will arrive after a >12 hr fast, settled into a quiet room for vital sign measurements and fasting blood sample collection. Following, a venous catheter will be implanted in forearm. A second fasting blood sample will be collected to be used as baseline measurement for postprandial outcomes. The participant will be provided with the test meal providing 928 kcalories and 60 g fat, 37 g protein and 60 g carbohydrate). with instruction to consume within 20 min under observation by the clinical research coordinator. After completing the test meal, the clinical coordinator will utilize a structured interview and questionnaires to assess changes of medications, mood and health status.The test meals will be in the form of a smoothie and reflect the diet assignment for that period by containing either 56 g walnuts or no walnuts[19, 61, 62, 81]. Walnuts will be finely ground for incorporation into smoothie.Baseline (fasting) levels of LPS, LBP and sCD14 will be measured from blood samples collected prior to meal (fasted). Blood samples will be obtained each hour following the completion of the meal. LPS changes after a meal; therefore, LPS will be measured in blood samples collected during the postprandial time period. Five hours after completion, the cognitive tests will be administered again. The remaining blood samples collected at each postprandial time will be stored at -20°C in case additional funding is obtained to analyze: lipoprotein cholesterol fractions, triglycerides, glucose, insulin, TNF-a, TNF-R2, IL-6, CRP, SI-CAM1, oxidative stress markers (e.g., 4-HNE, MDA) [19, 61, 62, 81] [57, 61, 81-83].Fecal samples will be analyzed for 16s rRNA in Objective 2. In addition, an aliquot of fecal sample will be stored at -80C in the event that funding becomes available to measure bile acids, especially deoxyocholic and lithocholic acids, two pro-inflammatory bile acids that are reduced after 3 weeks of consuming walnuts (42 g/day)[42].The clinical coordinator will collect all measurements including fasting and postprandial blood samples, anthropometry, vital signs, questionnaire data from ASA24 diet/activity recalls and food logs. Dr. Kiecolt-Glaser, a licensed psychologist, will oversee the administration of the NTCB prior to and following the test meal for pre-prandial and postprandial cognitive function. A product coordinator, who will not interact with participants at study visits, will organize and distribute study foods. Having a product coordinator minimizes the risk of dispensing errors. Fatty acid composition of plasma will be measured using gas chromatography [57, 58, 83, 87, 88]. Typical intra-assay coefficients of variation for plasma fatty acid composition is: palmitic acid (2.59), stearic acid (3.58), palmitoleic acid (5.58), oleic acid (2.84), LA (3.01), alpha-linolenic acid (6.07), eicosapentaenoic acid (8.69), docosapentaenoic acid (8.82) and docosahexaenoic acid (3.60).Participants will be asked to keep tally of study food consumption using a food log and will be instructed on the importance of maintaining her/his/their typical diet, physical activity habits and body weight throughout the study protocol. Habitual food intake data will be collected at Visit 1 using the DHQIII. Three unannounced ASA24 diet / ACT24 physical activity recalls will be conducted at random times during the study that will capture dietary intake during two weekdays and one weekend day. Adherence to consuming study foods will be assessed by three methods: 1) Study food intake logs; 2) Weight of unused study food returned; 2) Quantification of plasma fatty acids from blood samples for change of the unsaturated fatty acid, ALA and LA[53].Participants will be instructed to collect a fecal sample the night before or the morning of clinical visits 2,3,4 and 5. A fecal collection kit will be provided with specific instructions for how to store the sample until delivery to the clinic. 16s rRNA sequencing will be analyzed according to the method as recently described by[97]. The OSU Center for Microbiome Science core will perform DNA extraction, 16s rRNA sequencing and data analysis of a-diversity, b-diversity and relative abundance of phyla and species.The primary outcome used in sample size calculation is the postprandial cognitive test score measured at visits 3 and 5. Based on our previous study[19], we obtained the standard deviation (11.0) of the difference in postprandial cognitive test score between unsaturated fat meal and saturated fat meal[19]. With N=78, we will have 80% power to detect a difference of 3.5 in postprandial cognitive test score between control and walnut group using a two-sided paired t-test with type-I error of 0.05. To account for potential dropout, we will recruit 88 participants.Primary Hypothesis 1A: postprandial cognitive test score will be compared between control and walnut group using a two-sided paired t-test to account for the cross-over design. To further adjust for covariates, a linear mixed effect model with subject-specific random intercept will be fit on postprandial test score with the following covariates: study group, preprandial test score at visits 3 and 5, BMI, age, sex, education level and depression score. The regression coefficient of study group will be the adjusted difference in postprandial test score between study groups. Analyses for the primary hypothesis will use participants who complete the entire study, and will be based on intention-to-treat principal regardless of compliance and study group cross-over. Sensitivity analyses will be conducted with multiple imputation on missing values for participants who do not complete the entire study.Hypothesis 2A: A linear mixed effect model with subject-specific random intercept will be fit on change of endotoxemia during the 7-day intervention with the following covariates: study group, BMI, age, sex, and education level. The regression coefficient of study group will be the adjusted difference in reduction of endotoxemia between study groups.Patient randomization. We will randomize N=86 participants to either of the two orders of meal exposure: control followed by walnut or walnut followed by control.Measurement of primary outcomes. Primary outcome is postprandial global cognitive score measured at day 7 and 42 using the NIHMeasurement of secondary outcomes. Secondary outcomes include preprandial cognitive score measured at day 7 and 42, plasma sum of ALA+LA, endotoxemia, microbiome 16s RNA expression.