4 min read Doctors say people should expect to see a 1 to 3 pound weight gain in the first week or two of taking creatine. Initially, the rapid weight gain comes from water retention. Creatine is stored in skeletal muscle where it pulls water into muscle cells. With strength training, the increased weight gain will be from muscle rather than water. Research finds people can gain about 2.51 pounds in lean muscle mass. There is no scientific evidence of creatine increasing fat mass. Creatine is one of the most well-studied supplements, meaning doctors have a good grasp of its side effects. Weight gain is a well-known one, says Kristyen Tomcik, PhD , assistant professor of nutrition at the Case Western Reserve University School of Medicine. He says he experienced it personally during the first couple of weeks of going back on creatine after stopping the supplement for a while. The problem is whether the extra pounds is muscle or fat mass . With creatine, Dr.…