There are many factors, but one of the greatest is cravings which lead to excessive eating. When more energy - calories - are consumed than can be expended — burned off in a day, that excess energy is stored as fat. So we have to first look at what causes an excessive intake of energy or calories. I believe that unless cravings can be controlled, we'll eat more than we should and weight will be gained, which means that as long as excess calories are consumed, the weight can't be lost. Now, when cravings are involved, and I know that for me, my 3 addictions are ice cream, potato chips and fried chicken — all pleasures and reward treats from my childhood, we are dealing with controlling something that can go back years. So, unless I could get those cravings under control and minimize how much I eat, it would be a hopeless battle. Fortunately our leptin signaling has proven to do exactly that by being able to greatly reduce and control cravings.