As this is an old paper it may already have a thread, but I couldn't find it. Prebiotic evaluation of cocoa-derived flavanols in healthy humans by using a randomized, controlled, double-blind, crossover intervention study Xenofon Tzounis, Ana Rodriguez-Mateos, Jelena Vulevic, Glenn R Gibson, Catherine Kwik-Uribe, and Jeremy PE Spencer From the Department of Food and Nutritional Sciences, The University of Reading, Reading, United Kingdom (XT, AR-M, JV, GRG, and JPES), and the Analytical and Applied Sciences Group, Mars Inc, Hackettstown, NJ (CK-U). (my emphasis!) Abstract Background: The absorption of cocoa flavanols in the small intestine is limited, and the majority of the flavanols reach the large intestine where they may be metabolized by resident microbiota. Objective: We assessed the prebiotic potential of cocoa flavanols in a randomized, double-blind, crossover, controlled intervention study. Design: Twenty-two healthy human volunteers were randomly assigned to either a high–cocoa flavanol (HCF) group (494 mg cocoa flavanols/d) or a low–cocoa flavanol (LCF) group (23 mg cocoa flavanols/d) for 4 wk. This was followed by a 4-wk washout period before volunteers crossed to the alternant arm. Fecal samples were recovered before and after each intervention, and bacterial numbers were measured by fluorescence in situ hybridization. A number of other biochemical and physiologic markers were measured. Results: Compared with the consumption of the LCF drink, the daily consumption of the HCF drink for 4 wk significantly increased the bifidobacterial (P < 0.01) and lactobacilli (P < 0.001) populations but significantly decreased clostridia counts (P < 0.001). These microbial changes were paralleled by significant reductions in plasma triacylglycerol (P < 0.05) and C-reactive protein (P < 0.05) concentrations. Furthermore, changes in C-reactive protein concentrations were linked to changes in lactobacilli counts (P < 0.05, R2 = −0.33 for the model). These in vivo changes were closely paralleled by cocoa flavanol–induced bacterial changes in mixed-batch culture experiments. Conclusion: This study shows, for the first time to our knowledge, that consumption of cocoa flavanols can significantly affect the growth of select gut microflora in humans, which suggests the potential prebiotic benefits associated with the dietary inclusion of flavanol-rich foods. This trial was registered at clinicaltrials.gov as NCT01091922. Full text here NB This 2011 thread indicates that cocoa is not suitable for everyone.