...because I've read a few medical books 
  (randomly picked) and ended with contradictory
  reasonings and conclusion.

Could you list some of those books?

ps: I'm reading 'fats of life' by Glen Lawrence. I'll report if it gives a clear picture. One good thing from the first pages, is that it explains that fat is implied in a lot of subsystems. Fatty acids that are bad for your vascular system can help to avoid cancer, arthritis and other kinds of conditions... so it's not a one dimensional question. I like that.

Other than credential-spotting ( looking up how many esteemed institutions a person is associated with ) how does one decide whose book to even peruse and whose to dismiss.

Its really mind numbing that we have so much confusion in such an important space as nutrition.

Just look at the credentials of the expert that Ms.Teicholz [1] blames for this mess:

  Alice H. Lichtenstein is a senior scientist and director 
  of the Cardiovascular Nutrition Laboratory at the HNRCA, 
  as well as a Stanley N. Gershoff Professor of Nutrition 
  Science and Policy at the Friedman School. 

  Lichtenstein also serves as the executive editor of the 
  Tufts University Health & Nutrition Letter. 

  Education
  Hon. Ph.D., 2005, Faculty of Medicine, University of Kuopio (Finland)
  D.Sc., 1979, Nutritional Biochemistry, Harvard University
  M.S., 1975, Nutritional Biochemistry, Harvard University
  M.S., 1973, Nutrition, State College, Pennsylvania State University
  B.S., 1971, Nutrition, Cornell University

Ms. Teicholz was mentioned earlier in the discussion in the threads above.[2]

[1]

Nina Teicholz - 'The Real Food Politics'

https://www.youtube.com/watch?v=7Lww5WH7INI&t=12m26s

[2]

https://news.ycombinator.com/item?id=17794606

That's indeed an issue. I believe science is not immune to information overload (just like mainstream with internet). This creates spots / schools of thoughts, and only people working or studying the field can have an opinion whether a book or paper is worth its weight.

I guess it's a bit like music, unless you have genius talent out of the box, you will only be able to parse things clearly after 5-10 years of swimming in the pool. Unless we have something to connect the dots for us, for instance something that can cross correlated data from biological pathways, chemistry, physics, maths, so you know what is solid or not.

Also nutrition is too tied to economics and politics, that doesn't help.

You need to remember that a lot of the people like Alice H. Lichtenstein are heavily invested in the current thoughts on nutrition. I can not stress enough that "The Big Fat Surprise" is very informative about the current state of our nutrition policies here in the United States (and this leaks out of our country into many others that follow it by default). Just watch that "The Real Food Politics" video (see above).

Here is another article that specifically addresses this study,

http://www.zoeharcombe.com/2018/08/low-moderate-or-high-carb...

Zoe Harcombe takes a hard look at this study, and there are so many problems with this study, I am amazed that it was published, but wait, I would take a look at this,

https://twitter.com/WGyogaSC/status/1031258976560852992

This was a "paid to publish" study.

to you and parent, do you have sources beside pubmed to monitor medical knowledge ?

Since you are attacking me and not what I said, can I take there is no fault with my statement?

god, I'm not attacking, I'm asking you for your usual readings so I can learn too. Sorry if it came out as burden-of-proof statement

Humm one is cardiology book (in french) by jacques de praepe (I bought it), the others I don't remember, a mix of pubmed publications, lab textbooks on researchers webpage, youtube videos.