There are many factors and reasons why a person gain weight so fast. For instance, it’s very common among women to gain weight during pregnancy because their body expands and they have to consume more foods with good nutritional value for that will help the baby’s development under their belly. After birth they experience difficulty getting back to their pre-pregnancy body. Others gain weight too fast because of the food they eat which is basically the common reason for obesity. I think the genes can also be the reason why a person gain weight so fast. It easy to gain weight but extremely difficult to lose single pounds. You have to work really hard to attain your goal in losing weight and proper discipline as well. There are so many thing we can do to get back in shape. First is regular exercise. It may sound so hard as it requires determination and involve dietary planning to achieve your purpose. You can also try the surgery and pills. Well, whatever you have in mind I just want to wish you good luck!