Does anyone actually believe in the starvation mode theory?

I've been battling with this idea for months now. It all started when I tried to change my eating habits, which have always been pretty much low calorie with binges here and there. I want to be healthier and stop the binging, so I decided to check out Atkins. I was very unsuccessful on Atkins and actually gained weight following the induction phase of the plan as others said I should (high fat, moderate protein, low carb). I plugged my daily intake into a site that tracks calories/carbs/protein/fat, etc., and was told in the beginning that I wasn't eating enough calories or fat! I was eating at least 1100-1300 calories and I felt that my fat intake was a little high. My carbohydrate intake was 20 net carbs each day. So, I was told to increase my caloric intake to 1500-1800 and my fat intake to about 60% of total percentage of calories. I followed others menus and felt extremely full and ended up gaining 6 pounds after following this. I stopped Atkins! Here's my problem. I was told to increase my calories because my body was in "starvation mode". I think that is such an overused and misunderstood concept! If that were the cause then how does an anorexic end up being so extremely underweight? How does a person who had weight loss surgery like gastric bypass surgery lose weight? I'm not saying anorexia is healthy by any means and I know that a famished person has lost most muscle tissue and the metabolic rate has decreased, but they are STILL skinny by appearances!! They do not gain weight by decreasing caloric intake and yet I'm told that if I go below 1200 calories I will either gain weight or not lose any weight because my body is "holding on" to my weight because it thinks it's in "starvation mode". Is my body that efficient that in times of starvation, I will be overweight and never go below my ideal weight where an anorexic person has an inefficient body and can starve and turn skeletal?