Impact of coffee-consuming habits on plasma biomarkers in a healthy adult population

Increasing epidemiological evidence for the beneficial health effects of (poly)phenol-rich products has led to a growing interest in the role of (poly)phenols in reducing the incidence of chronic diseases. Coffee is a major contributor to dietary chlorogenic acids. However, the majority of these, unlike free phenolic acids, first need to be cleaved in order to be absorbed and about 70 % of them reach the colon intact where they are processed by the microbiota population. First, the analysis of major free phenolic acids in five commercially available soluble coffees is described. The influence of roasting and decaffeination and the contribution of free phenolic acids to the appearance of derived metabolites in plasma resulting from a pre-colonic absorption are then assessed. The hypothesis was that, as reported for chlorogenic acids, both roasting and decaffeination would have a negative impact on the quantified compounds. The contribution of free phenolic acids to the appearance of derived pre-colonic metabolites in plasma was hypothesized to be significant, as these are easily absorbed in the gastrointestinal tract. Results indicated that roasting and decaffeination reduce the amount of hydroxycinnamic acids, which in the amounts consumed with a regular coffee beverage do not significantly contribute to the early appearance of derived metabolites. The hydrolysis of 5-O-caffeoylquinic acid and 3-O-caffeoylquinic acid is a likely major contributing mechanism to the early appearance of derived metabolites in plasma. In a second stage, the impact of habitual consumption of popular (poly)phenol-rich products on human health and the impact of habitual consumption of coffee on the absorption and metabolism of chlorogenic acids were assessed in an observational human study with 62 healthy adult participants. The health status of the study population was assessed by the quantification of selected biomarkers of health using optimized methods, which were based on published protocols. The major hypotheses in this second section were that the metabolism of the biomarkers was stable over the study period (i.e. max 16 weeks); that subjects with a higher regular consumption of (poly)phenol-rich products have a healthier profile of biomarkers and that subjects with a higher absorption of coffee (poly)phenols have a healthier profile of biomarkers. A healthy and overall stable metabolism of the quantified inflammation and cardiovascular biomarkers (i.e. total aminothiols, glucose, insulin and uric acid) over a period of at least 8 - 16 weeks was confirmed. Subjects with a higher consumption were more likely to also be higher consumers of other (poly)phenol-rich products. A higher consumption of (poly)phenol-rich products was not associated with a better inflammatory and cardiovascular health profile, but the a higher presence of two colonic metabolites (i.e. vanilloylglycine and feruloylglycine) was associated with higher levels of glutathione. Overall, the results suggested a reduced bioavailability of chlorogenic acids with a higher habitual consumption of coffee including associated (poly)phenols, and encourage future investigations targeting the colonic microbiota populations.