So let's pick a common myth to start with. How about super foods?
Super Foods are any foods that are supposed to have the ability to cure diseases or keep you healthy on their own. The bad new? There is no such thing. Sadly it's a scam and you end up paying over the top prices for foods that really don't give you the supposed bang for your buck.
Even if a food is bursting with a beneficial nutrient, your body needs more than that to be healthy. There is also no official definition for what a super food is so it ends up getting used to market expensive trendy foods like goji or acai berries.
Some basic foods like apples can be equally as nutritious and a lot less costly. So enjoy a diet full of a variety of healthy foods. It'll do you and your wallet a good deal of health.