> Diets are not just about nutrition, that's one of the biggest misconceptions. Psychology and physical activities play equally, if not more important role in dieting.

This. With the addition that psychology is hugely affected human bodys tendency to defend agains weight loss. One good recent paper on the subject how much weight loss increased hunger: http://onlinelibrary.wiley.com/doi/10.1002/oby.21653/abstrac...