A “made easy” way of explaining meta analyses is “let’s look at all the studies done, adding up all the numbers and see how they go”. Some studies may say it works, others say it doesn’t. You can always choose studies that you KNOW can add up to a “doesn’t work” conclusion.

I imagine you know this, but for the benefit of your readers, meta-analyses are compilation studies in which researchers comb the medical literature for papers on a particular subject and then combine all the data from the individual studies together into one large study. This combining is often done to bring together a collection of studies, none of which contain data that has reached statistical significance, to see if the aggregate of all the data in the studies reaches statistical significance.

Meta-analyses are highly suspect, because they can lead to conclusions not warranted by the actual data. It’s always a good idea to take meta-analyses with a grain of salt.