tl/dr; Guy eats 5800 kcal every day of fat for 3 weeks, gains 1.3 kg and loses about an inch from his waistline, same guy eats 5800 kcal from carbs every day for 3 weeks, gains 7.1 kg and about 10 cm on the waistline. Exercise is supposed to be the similar in both cases.

Yes, it's just an anecdote, but an interesting one. And imho a reason to be a little humble about the things we think we know about how the human body responds to different kinds of foods. More research is needed.