Effect of simultaneous consumption of soymilk and coffee on the urinary excretion of isoflavones, chlorogenic acids and metabolites in healthy adults

• We investigated the effect of soy–coffee beverage ingestion on urinary phenolic metabolites.
• No effect was observed on excretion of isoflavone and chlorogenic acid metabolites when coffee and soymilk were mixed.
• A difference was observed between coffee and coffee–soy treatments when chlorogenic acid excretions were compared in urine.
• The addition of coffee to soymilk may decrease chlorogenic acid absorption in the upper digestive tract.
• The effect of soymilk binding properties on chlorogenic acid metabolite urinary excretion is milder than that of cow's milk.

The effect of the simultaneous ingestion of soymilk and coffee on the urinary excretion of isoflavones (ISO) and chlorogenic acids (CGA) was investigated for the first time in humans. In a randomized crossover study, soy (79.7 µmol ISO), coffee (561.2 µmol CGA) and soy–coffee beverage (79.7 µmol ISO and 561.2 µmol CGA) were ingested by adult subjects (n = 6) after overnight fasting. Urinary excretion of ISO aglycones and metabolites during 48 h after soy and soy–coffee beverages consumption was 22.0 ± 19.1 and 20.3 ± 9.4 µmol, respectively, with no difference between treatments. CGA and metabolite excretion during 24 h after coffee and soy–coffee beverage consumption was 3.4 ± 1.2 and 3.1 ± 0.6 mmol, respectively. However, a 42% decrease in levels of CGA and primary metabolites and not of colonic metabolites was observed in urine after soy–coffee beverage consumption compared to plain coffee, indicating that substances present in soymilk, most likely proteins, bind CGA reversibly, decreasing their absorption in the digestive tract.