How do most people accumulate excess body fat? When more food energy is taken in and not enough used, it's stored as fat. A factor to consider when determining obesity is genetics. Genetics makes a person more less likely to gain or lose weight. The environment plays a role as well. The circumstances that we encounter daily, push us towards fatness or thinness. Physical inactivity at home, work contributes to weight gain. Taking the elevator instead of the stairs contributes to weight gain.Technology has replaced physical activity. Watching television influences inactivity and little energy is required to use a remote control to change television channels. All of this factors from genetics , environment, physical inactivity may influence the causes of obesity. Clearly physical activity is necessary component of nutritional health.