1 Genetics. 2  Your genes may affect the amount of body fat you store, and where that fat is distributed. 3  Genetics may also play a role in how efficiently your body converts food into energy and how your body burns calories during exercise.4  Family lifestyle. 5  Obesity tends to run in families. Genetics. 2  Your genes may affect the amount of body fat you store, and where that fat is distributed. 3  Genetics may also play a role in how efficiently your body converts food into energy and how your body burns calories during exercise.