Dieting properly should start off with a complete physical and blood work. Why? To rule out other causes of weight gain and low metabolisum. An under active thyroid will be one cause. I know because I have that problem. I now have to take thyroid medication every morning. The thyroid is the main gland that governs your metabolisum and other organs. Since being on the daily medication for about 9 months now I have found that I can lose weight again. Did you know that an unchecked thyroid problem can cause major organs in your body to fail?
During your check-up ask your doctor about diabetes since many overweight people are prone to that. Special diets are to be followed for people with diabetes.