Insulin is a hormone that is secreted by the pancreas. It’s main functions is to help move nutrients from the bloodstream into target tissues and to regulate the blood glucose level.
When you consume carbohydrates, the glucose levels in your blood increase and your body produces more insulin. Insulin helps ‘carry’ the glucose to the tissues (e.g. the muscles) to be used as energy. But if it is not used, it is taken to the liver, where it is converted into fat for ‘storage’. This is why eating carbohydrates promotes fat storage, due to the insulin signals.