A susceptibility to gain weight may be written into molecular processes of human cells, a new study indicates. The proof-of-concept study with a set of 22 twins found an epigenetic signature in buccal or cheek cells appearing only for the twins who were obese compared to their thinner siblings. With more research, the findings could lead to a simple cheek swab test for an obesity biomarker and enable earlier prevention methods for a condition that effects 50% of U.S. adults, the researchers said.