The effect of black coffee on fasting metabolic markers and an abbreviated fat tolerance test

Abstract

Background & aims: Coffee is typically prohibited prior to metabolic assessment in clinical and research settings. However, whether coffee meaningfully alters fasted metabolic testing or the results of a fat tolerance test is unclear. We investigated whether allowing black coffee intake within a fast prior to blood work affected fasting triglycerides (TG) and glucose, as well as the postprandial lipemic and glycemic response following an abbreviated fat tolerance test (AFTT).

Methods: Participants completed two randomized AFTTs separated by at least 1 week. For each AFTT, participants arrived into the laboratory following a 10 h overnight fast and consumed either 8 oz of water or black coffee. Thirty minutes later, a baseline blood draw was collected. Immediately following, participants consumed a standardized high-fat shake (70% fat; 9 kcal/kg body mass), vacated the laboratory, and returned 4 h later for a follow-up blood draw.

Results: Ten healthy individuals (5M, 5F; age: 22.9 ± 3.8 years; BMI: 24.3 ± 2.6 kg/m²) completed the study. There was no difference between trials with regard to baseline TG (MD = 1.7 mg/dL; p = 0.74), 4 h TG (MD = 2.7 mg/dL; p = 0.75), Δ TG (MD = 4.4 mg/dL; p = 0.52), or % change TG (MD = 7.7%; p = 0.99). Similarly, following coffee consumption, baseline glucose was unchanged relative to water (MD = 0.4 mg/dL; p = 0.84) and there were no differences in postprandial glucose measures, including 4 h (MD = 0.9 mg/dL; p = 0.58), Δ (MD = 1.3 mg/dL; p = 0.31), and % change in glucose (MD = 1.6%; p = 0.29).

Conclusion: In our small study sample, coffee intake prior to an AFTT did not affect baseline or postprandial TG and glucose. Therefore, coffee intake prior to an AFTT may not affect its validity.

Keywords: Caffeine; Coffee; Glucose; Postprandial period; Triglycerides.