By Dr Ananya Mandal, MD
While lack of physical activity and increased intake of energy rich foods have been named as primary causes of obesity and overweight, there are other factors including hormonal and genetic influences that raise the risk of obesity.
Scientists have studied the important environmental and lifestyle causes of obesity as well as the genes that could increase the risk of obesity. Major efforts are now directed towards assessing the interactions of genes and environment that could be contributing to the rising number of obese individuals worldwide.
Obesity is the result of accumulation of body fat over time that results from chronic energy imbalance that arises due to calories consumed exceeding calories expended.
Obesity raises the risk of several relatively common diseases such as diabetes, hypertension, arthritis, heart disease, and some cancers.
The “thrifty gene” hypothesis
Scientists have found several genes that regulate how the body captures, stores and releases energy from food. The origin of these genes is ancient.
There is a concept of the “thrifty gene”. The theory suggests that the thrifty gene might have helped ancestors of present day humans survive occasional famines.
It is this same gene that is exposed to excess energy intake. It is now challenged by environments in which food is plentiful year round. This could result in increased storage of the energy in form of fat giving rise to the obesity epidemic.
Genes that influence obesity
However the thrifty gene might be part of a wide spectrum of genes influencing obesity. These genes can favor fat accumulation in a given environment. This may be proven by the fact that not all people living in industrialized countries with abundant food and physical inactivity are at risk of becoming obese.
Additionally not all obese people have the same body fat distribution or suffer the same health problems. This may be proven by racial or ethnic backgrounds as well as familial trends.
Genes determine regulation of appetite and satiety as well as tendency to be sedentary and a reduced capacity of using dietary fats as fuel and increased tendency of storing energy as fats.
Genetic studies of obese adults of different ethnic groups show that there are several associated genes in zones between chromosomes 2p, 7q, 10p and between q and p. The scans in obese children have shown that an association with a gene locus on chromosome 10p is the most consistent genetic finding.
There is a hormone called leptin that is released from the adipocytes in amounts proportional to the body weight. This hormone reaches the brain and binds with its receptors and plays a role in body’s capacity to use and store energy.
In the long term it leads to a decrease in appetite and an increase in heat generation from energy both leading to a decrease in obesity. Some populations with specific genetic makeup may be deficient in leptin or its receptors.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)
Last Updated: Apr 8, 2013