Social determinants of obesity

While genetic influences are important to understanding obesity, they cannot explain the current dramatic increase seen within specific countries or globally. It is accepted that calorie consumption in excess of calorie expenditure leads to obesity, however what has caused shifts in these two factors on a global scale is much debated.

Changing rates of obesity are related to a number of social phenomena including: social class, smoking status, number of children people have, and urbanization.

Social class
See Also : Social determinants of health in poverty

The correlation between social class and BMI varies globally. A review in 1989 found that in developed countries women of a high social class were less likely to be obese. No significant differences were seen among men of different social classes. In the developing world, women, men, and children from high social classes had greater rates of obesity. An update of this review carried out in 2007 found the same relationships, but they were weaker. The decrease in strength of correlation was felt to be due to the effects of globalization.

Many explanations have been put forth for associations between BMI and social class. It is thought that in developed countries, the wealthy are able to afford more nutritious food, they are under greater social pressure to remain slim, and have more opportunities along with greater expectations for physical fitness. In undeveloped countries the ability to afford food, high energy expenditure with physical labor, and cultural values favoring a larger body size are believed to contribute to the observed patterns. Attitudes toward body mass held by people in one's life may also play a role in obesity. A correlation in BMI changes over time has been found between friends, siblings, and spouses.

Smoking
Those who quit smoking gain an average of 4.4 kilograms (9.7 lb) for men and 5.0 kilograms (11.0 lb) for women over ten years. Changing rates of smoking however have had little effect on the overall rates of obesity.

Early malnutrition
Malnutrition in early life is believed to play a role in the rising rates of obesity in the developing world. Endocrine changes that occur during periods of malnutrition may promote the storage of fat once more calories become available.

Number of children
In the United States the number of children a person has had is related to their risk of obesity. A woman's risk of obesity increases by 7% per child, while a man's risk increases by 4% per child. This could be partly explained by the fact that having dependent children decreases physical activity in Western parents.

Urbanization
In the developing world urbanization is playing a role in increasing rate of obesity. In China, overall rates of obesity are below 5%. However, in some cities, rates of obesity are greater than 20%.