I've been dieting since 1971 (I was in kindergarten), and over the last 40, I've seen the pendulum swing back and forth between low-carb and low-fat several times.
Personally, I think scientists are still asking the wrong questions. Instead of "which diet is best," they need to be looking into "for whom."
A few diets attempt to address this, but far more research needs to be put into finding out WHY low-fat works better for some people, and low-carb works better for others. Is there a way to predict which diet a person will do best on, or will trial and error always be the best method?
I think we actually have to get rid of the "every diet will work, if you work it," mentality - but while it can be true, the reasons people find some diets unworkable needs to be addressed better.
I spent most of my life spinning my wheels, because I didn't know that low-carb was the best diet for me. I thought I just needed to put more effort into low-calorie. I worked harder, not smarter. I thought low-carb was unhealthy because I trusted my doctors' opinions. When my doctor recommended low-carb I was skeptical until I got a second opinion.
WOW, the difference is amazing. I just wish I'd learned this earlier in my life. It's hard to unlearn 40 years of habit (especially when we live in such a carb-heavy environment).