1. Age- Obesity can occur at any age and generally increases with age. Infants with excessive weight gain have an increased incidence of obesity in later life. About one third of obese adults have been so since childhood. It has been well established that most adipose cell are formed early in life & the obese infant lays down more of these cells than the normal infant. Hyper-plastic obesity in adults is extremely difficult to treat with conventional methods.

2. Sex- Women generally have higher rate of obesity than men, although men may have higher rates of overweight. Men are found to gain most weight between the ages of 29 and 35 years, while women gain most between 45 & 49 years of age, i.e., at menopausal age. It has been claimed that women's BMI increases with successive pregnancies. The recent evidence suggested that this increase is likely to be, on an average, about 1kg per pregnancy. On the other hand in many developing countries, consecutive pregnancies at short intervals are often associated with weight loss rather than weight gain.

3. Genetic factors- There is a genetic component in the aetiology of obesity. Twin studies have shown a close correlation between the weights of identical twins even when they are reared in dissimilar environments. The profile of fat distribution is also characterized by a significant heritability level of the order of about 50 percent of the total human variation. Recent studies have shown that the amount of abdominal fat was influenced by a genetic component accounting for 50-60 percent of the individual differences.

4. Socio-economic status- The relationship of obesity to social class has been studied in some detail. There is a clear inverse relationship between socio-economic status & obesity. Within some affluent countries, however, obesity has been found to be more prevalent in the lower socio-economic groups.