Fat cannot physically transform into muscle. Both fat and muscle are bodily tissues, but their structures and functions are very different. Fat tissue is made of fat cells that can grow larger, divide, remain constant or reduce in size.
Muscle tissue is composed of thousands of individual cells, called muscle fibers, that do not have the ability to divide or increase in number. However, muscle fibers possess the ability to change in size, functionality and density. Fat cells increase in size and number as a result of positive net calorie intake, while fat cell reduction is the result of negative net calorie intake. Net calorie intake is the difference between calories consumed and calories expended.