Postprandial metabolic responses to high-fat feeding in healthy adults following ingestion of oolong tea-derived polymerized polyphenols: a randomized, double-blinded, placebo-controlled crossover study.

BACKGROUND: Polymerized polyphenols (PP) found in oolong tea can inhibit pancreatic lipase activity in vitro and pilot work indicates this may reduce postprandial lipemia. Since tea contains caffeine and catechins, the interactions between these ingredients and PP warrants investigation.

OBJECTIVE: Assess whether PP ingested alone or with caffeine and catechins lowers postprandial lipemia.

DESIGN: Fifty healthy adults (mean (standard deviation) age: 26 (7) years; BMI: 24.0 (2.7) kg/m2 ; female n=16) completed 4 oral lipid tolerance tests in a placebo-controlled randomized, crossover design. Participants ingested 40 g fat with either: 1) placebo; 2) 100 mg PP; 3) 150 mg PP; or 4) 100 mg PP plus 50 mg caffeine and 63 mg catechins (PP+CC). Blood was sampled for 3 hours postprandially to assess concentrations of serum and plasma triacylglycerol and plasma markers of lipid (non-esterified fatty acid (NEFA), glycerol, low- and high-density lipoprotein-cholesterol (LDL-c & HDL-c), and apolipoprotein-AI, -AII, -B, -CII, -CIII and -E) and glucose metabolism (glucose, insulin, and C-peptide).

RESULTS: Serum and plasma triacylglycerol concentrations and lipid metabolism variables generally increased following any test drink ingestion (main effect of time, p<0.001). Nevertheless, for the lipid metabolism responses, there were no statistically significant condition x time interactions and no statistically significant differences in incremental or total area under the curve between conditions, apart from HDL-c (p = 0.021). Ingesting 100 mg PP+CC lowered peak plasma glucose, insulin, and C-peptide concentrations versus all other conditions 30 minutes post-ingestion (p<0.001), with persistent alterations in glucose concentrations observed for 90 minutes compared with placebo and 100 mg PP conditions.

CONCLUSIONS: PP ingested at doses up to 150 mg do not clearly alter early-phase postprandial triacylglycerol concentrations in healthy adults, irrespective of the presence or absence of caffeine and catechins. Nevertheless, caffeine and catechins added to PP lowered postprandial glucose and insulin concentrations.

CLINICAL TRIAL REGISTRATION: https://clinicaltrials.gov/ct2/show/NCT03324191 (NCT03324191).