Alzheimer's disease (AD) is the most common form of dementia. H. pylori infection and overweight have been implicated in AD via the gut-brain axis (GBA). This study aimed to determine whether supplementation of BRBs has a meaningful effect on H. pylori infection, overweight, and AD development in a clinical trial setting. We conducted a randomized placebo-controlled clinical trial in patients with mild clinical dementia who also had H. pylori infection and were overweight. The study was conducted over 10 weeks, consisting of an 8-week intervention period (25 g powder of black raspberries, BRBs, or placebo twice daily, morning and evening) and a 2-week follow-up. The primary outcomes were changes in Clinical Dementia Rating (CDR), Urea Breath Test (UBT), and Body Mass Index (BMI). Consumption of BRBs improved cognitive functions (p <
0.00001), compared to the placebo group (p >
0.05). Besides, BRBs ingestion decreased H. pylori infection and BMI (p <
0.00001 and p <
0.05 respectively) while the placebo group stayed statistically the same (p = 0.98 and p = 0.25 respectively). BRBs significantly decreased inflammatory markers, improved oxidative index, and adiponectin (p <
0.05) compared to the placebo group, while adenosine monophosphate-activated protein kinase (AMPK) and leptin did not significantly change. BRBs modulated the abundance of several fecal probiotics, particularly, Akkermansia muciniphila. Our results provided that BRBs suppressed H. pylori infection, decreased BMI, and rebalanced the gut microbiome, which could improve cognitive functions in mild dementia patients. Longer and larger randomized clinical trials of BRB interventions targeting H. pylori infection, overweight, or mild dementia are warranted to confirm the results from this pilot trial. Trial Registration: ClinicalTrials.gov identifier: NCT05680532.