When evaluating resources you have to remember that you're not just a consumer, you're a researcher. This means working to understand bias, context, and issues surrounding the topic that you're studying.
For instance, dietary and nutritional information seems to be constantly changing. Why might this be? If I had to guess it would have to do with how difficult the studies are to conduct, who stands to gain by influencing the narrative and that our understanding of medicine is changing as well. It can be difficult for those with access to scholarly journals to sort out the data and almost impossible for the consumer.