How does the Mediterranean Diet impact the gut microbiome and cognitive performance African American obese adults?

In a recent study published in the Nutrients Journal, researchers examined the data from the Building Research in Diet and Cognition (BRIDGE) trial to determine the effects of the Mediterranean Diet (Med Diet) and intentional weight loss (IWL) on the gut microbiome and cognitive function in African American obese adults.

Study: Exploring the Effects of a Mediterranean Diet and Weight Loss on the Gut Microbiome and Cognitive Performance in Older, African American Obese Adults: A Post Hoc Analysis. Image Credit: luigigiordano/Shutterstock.com

Background

Alzheimer's dementia (AD) affected one in nine Americans over 65 in 2022. By 2060, this proportion is projected to increase to one in seven older individuals.

African American adults have higher AD risk factors than non-Hispanic whites and Hispanics, including obesity and poor food quality. Detecting AD and ADx early, during the mild cognitive impairment (MCI) period, has been the focus of AD prevention.

Diet and weight are risk factors for AD, with the Western diet increasing amyloid-beta levels and cerebral perfusion. A Med Diet and IWL diet has been shown to protect against AD and improve cognitive performance.

A Med diet reduces inflammation, oxidative stress, and cognitive performance, all risk factors for AD. The gut microbiome may boost cognition with a Med diet and IWL, increasing microbial diversity and fecal anti-inflammatory compounds, including butyrate.

However, no study has examined how the Med diet lifestyle intervention affects the gut microbiome of African American obese people or how these changes relate to cognitive abilities.

About the study

In the present study, post hoc analysis of the BRIDGE trial was performed to examine whether intervention participation affected gut microbiota structure, abundance, butyrate production potential, and cognitive function. 

The research team divided 185 participants into three cohorts of 60. It randomized them to a lifestyle program following a Med Diet (MedA), a Med diet while limiting calories to generate IWL (MedWL), or a usual diet. Throughout the 14-month intervention, participants were instructed to keep up their diet and exercise routine.

The MedWL and MedA groups baseline food habits and eight-month stool microbiomes were investigated. Genomic Deoxyribonucleic acid (DNA) was extracted from the samples and subjected to targeted amplicon sequencing to analyze the V4 region of the 16S ribosomal ribonucleic acid (rRNA) gene. The data obtained from the sequencing were analyzed using statistical tools to determine the abundance of different taxa.

The authors also examined the levels of the Butyryl-CoA-transferase (BcoA) enzyme involved in microbial butyrate synthesis using real-time polymerase chain reaction (PCR).

Additionally, various health and cognitive measures were assessed, including inflammatory markers, blood glucose levels, cognitive tests, and depressive symptoms.

They also examined high-sensitivity C-reactive protein, hemoglobin A1c, fasting serum glucose, blood pressure, anthropometrics, and body composition. The Harvard Food Frequency Questionnaire (HFFQ) measured food habits at baseline and post-intervention.

Diet and lifestyle decisions affected metropolitan Midwestern people's gut microbiome and cognitive performance. The team used a linear mixed-effects model for normal and continuous variables, while a generalized linear mixed model was used for nominal variables.

The CAUSALMED approach of the Statistical Analysis System (SAS) tool was used for regression adjustment and generalized linear models to estimate the significance and degree of the mediating impact.

Results

The present work analyzed an eight-month intervention on the Med diet lifestyle, focusing on older African American obese women. The results show minimal impact on the gut microbiota composition, with a significant group impact on alpha diversity but no significant effect on beta diversity or taxonomic abundance.

A correlation was observed between increased Med diet adherence score (MED score), learning, memory, and recognition (LMR) score, and a subsequent decrease in alpha diversity. This is consistent with earlier studies showing minimal gut microbiome variety and composition alterations. The MedWL group, which experienced weight loss, showed gut microbiome changes associated with anti-inflammatory effects.

The Med diet interventions also positively affected cognitive performance, particularly in mental abilities such as attention, executive function, and learning and memory.

However, the study has limitations, such as weight loss in the MedA group and the limited sample size, as well as the lack of randomization and self-reporting of food intake.

Conclusion

The present investigation demonstrated that adopting a Med diet, with or without calorie restriction, can benefit the gut microbiome and cognitive performance.

The findings suggest that dietary interventions could be used to improve the gut health and mental abilities of individuals.

However, further research is needed to explore the underlying mechanisms and to support the implementation of dietary interventions in clinical settings.

Written by

Susha Cheriyedath

Susha has a Bachelor of Science (B.Sc.) degree in Chemistry and Master of Science (M.Sc) degree in Biochemistry from the University of Calicut, India. She always had a keen interest in medical and health science. As part of her masters degree, she specialized in Biochemistry, with an emphasis on Microbiology, Physiology, Biotechnology, and Nutrition. In her spare time, she loves to cook up a storm in the kitchen with her super-messy baking experiments.