The stars in an app store tell you whether people liked the app. They do not tell you whether its health information is accurate.
How to read reviews:
Read the 2- and 3-star reviews first: they are often the most specific.
Look at the date of the last update, under What’s New. You should see a recent date, within the last year.
Look for who made the app: the publisher’s name is written under the title. A hospital, a government or a university is easier to verify than an unknown name.
If you don’t see it: an app with no update for a long time may contain outdated information. A stable date does not mean the app is abandoned: check the publisher’s website as well.
Limitation: reviews can be bought or fake. Many identical reviews, posted on the same day, are a warning sign.
To picture it: five stars for a cake mean it tastes good, not that it is good for your health.