We need evidence from high-quality studies on groups of people rather than from theory alone. And be aware of the vested interests of information sources. What matters is not whether someone famous recommends a particular product, but whether there is evidence from randomised controlled trials showing that it is more likely to do good than harm. Assessing medical research can be complex - even for the experts. It helps to understand some of the more common pitfalls.
Anecdotal evidence can be dangerous.
You cannot infer a general rule from a single experience - especially someone else's. Many diseases get better with or without treatment. The placebo is powerful. This makes it difficult to discern the real effects of active treatments without randomised controlled trials. Screening tests that detect early disease are not always beneficial.