I saw yet another study the other day showing how a high protein intake can help with short-term weight loss. This has been shown probably dozens of times, where if someone is on a reduced calorie diet, higher protein helps through reduced hunger and better retention of lean mass.
What these studies are not addressing is how high protein intakes may affect long-term weight regulation. For example, this new study shows that higher protein intake in adults is correlated with higher body fat. People can pick apart this particular study if they like, but if you look at different studies, you tend to see higher protein intake correlated with higher BMI/body fat.
I think someone else (maybe Perfect Health Diet?) was brave enough to write about this before. Is a high protein intake really that beneficial in the long run?
Here's another way to think of it: if protein is the key to weight regulation, then how can there be cultures that eat moderate or even low-protein and yet still maintain normal weights. This would suggest that either protein is not the key to weight regulation that people believe it is, or there are multiple macronutrient paths to a stable body weight.
Either way, I think it's a lot more complex than just, "eat more protein and lose weight". I remember another study (don't have time to dig it up now), where subjects started on a high-protein intake but then after a year or so ended up back to consuming moderate levels of protein. You could interpret this as either subjects going back to their old habits, or perhaps they grew weary of consuming high protein.