# Coffee Roast Level, Timing, and Carbohydrate Source Affect Peak Blood Glucose and Area Under the Curve Values in a Randomized Pilot Clinical Trial

## TL;DR

This study shows that coffee roast level, timing, and carbohydrate type affect blood glucose levels, with implications for managing glucose for exercise or health.

## Contribution

The study is the first to investigate how coffee roast level, timing, and carbohydrate source interact to influence blood glucose responses in humans.

## Key findings

- Pre-CHO coffee treatments produced the highest peak glucose values (160 mg/dL).
- Medium roast coffee significantly reduced AUC values in the CoO combination.
- Three AUC main effects and two interactions were highly significant (p < 0.002).

## Abstract

Roasted coffee's bioactive compounds may affect human glucose metabolism. This pilot clinical trial investigated the impact of coffee roast level, coffee timing, and carbohydrate (CHO) type on blood glucose responses. Healthy participants (15 female and 4 male) completed this six-week, randomized, single-blinded study. Treatments comprised combinations of roast levels (light, medium, or dark), coffee timings (pre-, co-, or post-CHO ingestion), and CHO types: oral glucose tolerance test (OGTT) beverages or a standardized breakfast designated as PreO, PreB, CoO, CoB, PostO, and PostB. Subjects consumed 300 mL of test beverages and provided 10 capillary blood samples over 4 h. Coffees were analyzed for caffeine, 3, 4, and 5 chlorogenic acids (CGA), trigonelline, total phenols, color, °Brix, and total dissolved solids (TDS). Significant (p < 0.05) differences in 3CQA, 5CQA, and trigonelline, but not caffeine and 4CQA, were observed across roast levels. Prior to CHO, coffee did not increase blood glucose, but potentiated increases after CHO. PreO and PreB treatments produced the highest peak glucose values (160 mg/dL). This was not observed for co- or posttreatments. In the CoO combination, AUC values were significantly (p < 0.05) lower than placebo only for medium roast. In posttreatments, peak glucose levels were higher following OGTT than breakfast, but AUCs did not differ. Light roast coffee yielded the lowest AUC for PreO and the highest peak at 3 h in the CoO combination. Medium roast resulted in the lowest AUC across all time points in CoO, while both medium and dark roasts elevated AUC in PreO. Only dark roast increased AUC in the PreB condition. Three AUC main effects (CHO type, coffee roast, and timing) and two interactions (timing × roast; timing × CHO × roast) were highly significant (p < 0.002). These findings may benefit those desiring temporary blood glucose elevations for exercise performance and recovery versus those seeking to moderate glucose.

Trial Registration: ClinicalTrials.gov identifier: NCT05119153