Hormonal

Low baseline sympathoadrenal activity, indicated by low 24-hour urinary norepinephrine and epinephrine excretion rates, is associated with greater subsequent body weight gain and increased central adiposity (waist-to-thigh ratio) in humans.

If you have a history of easy weight gain, your body may naturally operate with lower sympathetic nervous system activity, which reduces energy expenditure and promotes fat storage, particularly around the waist. This is a biological predisposition, not a failure of will. To counter this, you may need to be more consistent with physical activity and dietary management than others, as your body is less efficient at burning off excess calories at rest.