Genes- a small percentage of obese cases can be attributed to genetic factors.  This include mutations in the leptin gene and its receptor, or the melanocortin system. The onset of obesity in these cases usually occurs at an early age.  In these cases, obesity can be attributed to over-eating instead of defects in energy expenditure.

One third of the variance in BMI may be due to genetic factors. 

Metabolism- Studies have been shown that obese people have higher metabolic rates than their non-obese people. 

Behaviour- obesity is a result of energy intake exceeding energy needed.  Many overweight people eat in response to boredom, loneliness or stress. 

Physical Activity- physical activity brings important health benefits.  Obesity can be attributed to failure of the homeostatic mechanisms to match energy intake to the body’s energy needs.

Environment- increase in obesity is linked to “economic development suggests that we have a latent susceptibility to obesity.”  Cultures around the world, when introduced to western cultures rapidly gain weight and develop diabetes.  Overweight tends to run in the family, which results from genes and shared lifestyles.