I had the same fear. I was on low-fat paleolithic (lean-green) diet from spring to fall of last year and lost 20+ lbs in 6 months.
In mid-September I went to high-fat primal (fat-green) diet and lost additional 30+ lbs in 3 months.
I think it has something to do with fat stimulating leptin which boosts metabolism via thyroid, adrenals, and hypothalamus.
I have begun to stall again but I think I have a fix.