In conjunction with exercise, what's the best diet for losing weight and slimming down?

Based on Literature: If you look at the literature the evidence seems to suggest that diets focusing on higher protein intake, and less carbs tends to be more effective. Also, meal replacement have been shown to be superior to meals prepared by patients in losing weight (as long as the company is legit). Other things that help: Keeping a diary, documenting weight regularly, exercise, medication, behavioral tx, etc.