There is this common idea that overweight people are greedy, but in most cases that is far from truth. Most people lead fairly sedentary lifestyles and calorie (energy) needs may not be great. Eating just a small amount more than those needs will result in a slow but steady weight increase.
Eating just 100 calories a day more than her needs (represented, say, by a banana or one large chocolate biscuit) will result (all other factors being equal) in an annual weight gain of 4.7kg (10lb)!
As we get older, our metabolic rate also slow down a little very gradually, which can result in slow weight-gain in people aged 30 plus.
Is it really possible that there are people who, due to genetics, are obese but do not and have never overeaten? We don’t think so. Our definition of “to overeat” is to eat more fuel/energy/food, as measured in calories, than your body expends, as measured in calories. How might genetics play a role in obesity? Genetics might create a compulsion to overeating. Genetics might make you more prone to depression, which is associated with overeating and a sedentary lifestyle. And finally, genetics might make your body’s metabolism somewhat more efficient, using fewer calories to get through the day, lowering the number of calories you can eat before you “overeat.”