The accumulation of fat is produced as a consequence of the energetic imbalance in which the energy presented as calories represents the energy expends by the basal metabolism (the consumption of calories of the organism in resting conditions), thermogenesis (body warming) and the caloric consumption derived from the physical activity.

When food consumption increases, or the energy expended decreases, the calories that the body doesn't need turn into fat. In most cases obesity is generated most commonly by eating a diet high in fat and calories, being sedentary or both; all of this works together with the factors mentioned above.

Very frequently circumstances that induce anxiety come along with a compulsive eating attitude, which leads to a future over weight condition.

Giving up a smoking habit could very frequently lead to weight augmentation too, but this can be prevented.
 
Nevertheless, we must say that nowadays we can use the word "secondary obesity" for cases in which this disease is originated by other pathologies that keeps the fat in the organism.

In this regard we primarily have the Cushing's syndrome, which is a disorder characterized by the extreme production of cortisol, causing the body to go through several changes leading to an abnormal fat accumulation; Hypothyroidism, among others.