The only proof I have is an anecdote but it is consistent with my research-- and I've lost 100 pounds in 8 months as a result. The biggest problem is we have rejected science from food to begin with. We have government spending billions pushing a diet designed to create obesity (which is very high in carbs, effectively sugar, and low in fat.) Likely there are at least two types of people biochemically- those who are…
Also I tried looking this up and failed. But I'm sure that leptin wasn't discovered until the war on fat was well underway. And the first instinct when it was discovered was to try to use it as a drug target (all these failed badly).