A leading cause of weight gain is insulin resistance. Insulin is a hormone that transports glucose into our cells so that the cells can burn the glucose as fuel. When we bombard our cells with insulin by eating lots of carbs, our cells stop letting the glucose in. When the glucose gets stuck in circulation, it eventually gets sent to storage in the form of fat. At the same time, the cells are still hungry for energy so signals are sent to the brain for hunger. A vicious cycle has begun that leads to increased fat deposition and fatigue.
The key to restoring the sensitivity of the cells to insulin is to reduce carb consumption for a long enough time. There are also natural substances, such as alpha lipoic acid, vanadium and chromium, that enhance the process.
Determining the specifics of the process can be a little tricky so it is best to have doctor supervision.