Consuming an excess of simple sugars, as well as overly processed and refined carbohydrates, is a perfect way to train your body to store and retain fat. You may think that fat free cookie is a good choice, but if the first two ingredients are white flour and sugar, eating that cookie will result in a spike in your blood sugar (glucose) levels. When this happens, your pancreas secretes insulin, which is a storage hormone. It takes that glucose and stores some in the muscles and liver as glycogen (your main energy source), and then stores the remainder as fat. Your pancreas is also in charge of producing another hormone called glucagon. This is a release hormone, which is used to mobilize stored fat to be used for energy. When you force your pancreas to spike insulin production to keep up with your ingestion of simple sugars, it has to back off of glucagon production, negatively impacting your ability to release and burn fat.