How to select secondary resources to include in Literature Review?

Hi All!
I’m currently pursuing a research project on Diet and Nutrition, particularly on how different food types increase or decrease the likelihood of heart disease. The purpose of the study is to further existing research in the field and eventually help nutritionists in designing diet charts for patients of heart disease. I have begun writing a literature review for my proposal but can’t seem to narrow down the secondary resources I should include in the review, the large number of resources available on the internet is confusing me. I have gone through a lot of journals on the subject but am having a tough time selecting research articles. How does one figure out which resources are reliable and will go well with my topic? Can anyone provide some tips to help me with the selection process?