Background <p>Haskap berries have great potential as a superfood due to high polyphenolic content which confers both anti-inflammatory and antioxidant activity. These health impacts are mitigated, at least in part, by the gut microbiome as most ingested polyphenols pass to the large intestine for microbial enzymatic action and conversion to secondary phenolic metabolites. These microbial actions mediate both the bioavailability and the bioefficacy of Haskap-derived phenolics. However, clinical intervention trials characterizing the impact of long-term Haskap consumption on human health and the interaction between Haskap-derived phenolics and the gut microbiome are limited. This study aims to determine the impact of Haskap consumption on gut microbiome composition, gut microbial and serum metabolites, and other health outcome metrics in a cohort of adults with both low and high risk of metabolic syndrome.</p> Methods <p>This is a four-armed, randomized, triple-blind, placebo-controlled clinical trial conducted in a cohort of adults with both low and high risk of metabolic syndrome. A total of 120 participants (60 metabolically healthy, 60 metabolically unhealthy) will be randomized in a 1:1 ratio to consume a daily dose of either Haskap or placebo juice for 8 weeks. Outcome measures will be collected before and after the intervention period to determine the health impacts of Haskap in both groups. Primary outcome measures include fasting blood markers of glucose and lipid metabolism and inflammation, fat oxidation rates during submaximal exercise, 16S rRNA fecal microbial composition data, and mass spectrometry-acquired fecal and serum metabolomic data. Secondary outcome measures include anthropometric and sleep quality measures as well as acute and habitual dietary intake data.</p> Discussion <p>Investigating how the gut microbiome influences the health benefits of consuming Haskap berries will help elucidate potential mechanisms of Haskap-induced metabolic health benefits and help inform the development of effective strategies to decrease metabolic disease risk through Haskap consumption.</p> Trial registration <p>ClinicalTrials.gov NCT06546020. Registered on 1 August 2024.</p>