Roasting intensity of naturally low-caffeine Laurina coffee modulates glucose metabolism and redox balance in humans

Objective. Coffee consumption is negatively associated with risk of type 2 diabetes and cardiovascular mortality. Coffee roasting can greatly modify the quality-quantitative characteristics of bioactive compounds. We compared the effects of two different roasting intensities of the same naturally low-caffeine Arabica coffee variety (Laurina), on glucose and lipid metabolism as well as oxidative stress. Research Methods & Procedures. We performed a double-blind, crossover intervention study. 14 healthy male volunteers consumed 4 cups/day of Light Roasted Coffee (LRC) and Dark Roasted Coffee (DRC) for one-week (intervention period 1 and 2 respectively). One-week washout, with total abstinence from coffee and other possible caffeine sources, preceded each interventions. Data were collected at the end of washout and intervention periods. Results. Changes between washout and intervention periods in glucose concentrations at 2-h 12 post-OGTT, were significantly lower following DRC than LRC intake (-0.6±0.3 and 0.4±0.3 mmol/l, p<0.03). Changes in β-cell function, assessed as insulin secretion-sensitivity index-2 (ISSI2), were significantly greater following DRC than LRC (34.7±25.0 and -18.8±21.0,p=0.03). The initial (30 minutes) post-OGTT AUC of glucagon-like peptide-1 was 24±9% greater (p=0.03) after DRC than LRC. LRC or DRC did not affect insulin sensitivity. Changes from basal of reduced-to-oxidized glutathione ratio (GSH/GSSG) in erythrocytes were significantly greater after DRC than LRC (+1437±371 and -152±30, p<0.05). The omega-3 index in erythrocyte membranes was 16±4% greater (p<0.001) after DRC than LRC. Conclusions. DRC consumption improved post-load glucose metabolism by increasing incretin and insulin secretions. DRC compared to LRC improved redox balance and increased omega-3 fatty acids. Thus, we suggest greater metabolic benefits related to DRC.