You can safely ignore all advices that tell you eat this and eat that especially coming from people who don't a problem putting on weight.
There are many many factors in play and you have to address them as a whole not just eat this and eat that.
Factors like quality of stomach acid, gut flora, hormone imbalances, liver functions, quality of enzymes, stress levels, both physical and emotional, genetics, heavy metal overload, etc.
I did manage to get some fat levels under my skin but it took very long time. The best thing that works for me is 60/40 meat/fat by volume. The amount of serving does not appear to matter. Also, I quickly lose weight under stress.
So everyone is different and you have to figure it out what works for you on your own.