Here's a little-known secret:
Significant, long-term, non-surgical weight loss is so rare it is essentially a myth. Here's the stats on the diet rate highest by U.S. News:
http://health.usnews.com/best-diet/dash-diet. Those in the most successful diet lost an average of 19 pounds. If you weigh over 300 lbs and lose 50, you may still qualify as obese. Obesity changes your body and there is some research to suggest that obesity is a symptom of underlying health issues that will always cause your body to both proccess and crave food differently that people who are a normal weight. The only way to lose more than a modest amount and keep it off long term is either surgery accompanied by significant lifestyle changes or essentially an eating disorder.