Obesity is a complex disease for which no single cause or cure exists. You gain weight when you take in more calories than you burn off. But obesity is influenced by many other things, including:
Obesity has a strong genetic component. Offsprings of obese parents are much more likely to become obese than offsprings of lean parents.
This is not to say that obesity is completely predetermined because our genes aren’t as set in stone as you may think… the signals we send our genes can have a major effect on which genes are expressed and which are not.