Regarding your second paragraph, that is perhaps because different experiments give different results. When it comes to such things no experiment can be perfect because it is so hard to isolate completely the dependent variable. So in most cases is probabilities. It is safe to suggest say 250mg if the majority of experiments get roughly that results.

Considering the above and considering that scientists do not seem to agree because the experiments do not seem to give the same results, what made Tim Ferris the arbiter?