Grahamsphillips I should have been more clear, I did not mean the gut microbiota, but what people in Personal Care, a business with a turnover of $4-500 B yearly have taken on board and without much munching around made claims that are, mildly speaking, difficult to prove. The gut microbiome has been subject of research for many years and some success stories have proven its significance.
I would be interested in knowing how or whether caffein improves/enthuse the microbiota.