When someone says “studies show,” the obvious next question is: which studies, and how good were they? Most health confusion comes from treating every study as equally trustworthy. They aren’t.

Here’s the rough hierarchy this blog uses, strongest first:

1. Systematic reviews and meta-analyses of randomised controlled trials — many human trials pooled together.
2. Large randomised controlled trials (RCTs) in humans — the gold standard for “does X cause Y.”
3. Observational/cohort studies — useful for spotting patterns, but they show correlation, not cause. Confounders hide everywhere.
4. Animal and cell studies — generate ideas. Most things that work in a mouse never work in a person.
5. Anecdote and tradition — zero evidentiary weight, however compelling the story.

A single study, at any level, rarely settles anything. Replication does. When you read “a new study found…”, the honest reaction is curiosity, not a diet change.