They fed pigs four different diets that had the same amount of calories, but varying ratios of n3/n6 fats.
The pigs with high n6/n3 ratio ended up much fatter and less muscular than the pigs eating a 1-1 ratio diet. It's a very neat demonstration that "all that matters is calories" is not true; your metabolism, and thus how you use the calories, is influenced by the kinds of calories you are eating.
Well, at least if you are a pig. But it seems likely the same holds true in humans, though AFAIK no one has yet tried to do a similar controlled trial in humans.
But there's lots of assocational evidence that lines up in the same direction -- e.g., in America we've been getting fatter pretty much in-lock step with increasing consumption of n6 fats & there is a correlation between body-fat composition (which itself follows fat composition from the diet) and obesity.
So, in the light of the above, my #1 weight loss tip is: eat fewer n6 fats. (In practice, this means avoiding most prepared processed foodes and being extremely selective if eating out (since restaurants tend to go crazy using vegetable oil as a cooking fat, which is super high in n6 fats).)
The pigs study:
https://www.cambridge.org/core/journals/british-journal-of-n...