A randomised, placebo-controlled, double-blind, cross-over human intervention study will be conducted in 20 healthy human volunteers to test the impact of a high-flavanol containing meal on the growth of the large intestinal bacteria (microflora). The high flavanol test meal will contain 495 mg of flavanols and the low flavanol control will contain 23 mg of flavanols. The two intervention diets are otherwise matched for macro- and micronutrient content. Changes in the gut microbiota will be determined by measuring bacterial population levels in human faecal material using 16S rRNA targeted oligonucleotide probes and fluorescence in situ hybridization. A number of other biochemical and physiological measures will be recorded including blood glucose, lipoproteins, cytokine levels and blood pressure.