Professor A.H.G.s. Udari please do not think I am being flip but where in the world are we discussing? There is a vast difference between study sizes in the United States as compared to Europe and the rest of the world. In the States, the studies are in the thousands wherein in France, Spain, or Germany, etc. studies routinely are composed of 20 to 60 participants and are published. Sure there are many European projects that involve thousands or hundreds of thousands but the difference is that more attention is given to the structure and protocols of the experiment than sheer numbers. Plus with dietary experiments, it is very hard to verify subjects' compliance. Sure in the Framingham nurses' study there were vast numbers and over generations, but how reliable were the comments on say how many orange juice glasses per week or amounts of dietary iron in a country that over fortifies just about everything. Small studies can control better the food intake at least in theory. Plus, of course, If you obtain promising results then larger studies are the order of the day. Hope that helps

CG Yukna

Studies with large participants provide promising plus reliable results. However there is no gold standard in terms of sample size as each study comes with its own inter- and intra sample variations based on the features that being collected during the study. Since this is a clinical study, a power analysis on data from few prominent clinical variables (potential con-founders that may explain differences in microbiome composition) collected from the cohorts of interests may provide few hints on how many samples to be included in a microbiome study to anticipate statistically significant results. Yet, this could be a superficial test to explain how different the study groups are based on certain variables.