Your client owns an online nutrition membership program for women, where customers get tips, diets,...

Facebook Pixel allows you to track events, or specific actions, people take on your website. 

For this specific case, you should use the View Content Event pixel to track specific visits to the blog posts.

You can use URL's for your ads afterward as well; however, once you have +25 blog posts, using URL's becomes unpractical.

Here is the list of the 9 standard events you can use:

For more detailed information you can view the following Facebook for developers post: https://developers.facebook.com/docs/ads-for-websites/pixel-events/v2.11