Extreme obesity shortened life expectancy by eight years, while obesity and overweight reduced six and three years from a person's total life span.lwpkommunikacio/Flickr

Certain genes play a crucial role in overeating and obesity in childhood, researchers from Canada said. 

Poor food choices are often blamed for making a person overweight or obese. Researchers from McGill University and University of Toronto in Canada, looked at 150 children aged four and found that many other factors including genetic predispositions, and stress, contributed widely to obesity.

The findings are expected to help prevent childhood obesity and provide better interventions. "In broad terms, we are finding that obesity is a product of genetics, early development and circumstance",  Professor Michael Meaney from the McGill University, said in a statement.

The participants in the study were born to women who were enrolled in the Maternal Adversity Vulnerability & Neurodevelopment (MAVAN) project. The project looked at pregnant women who were depressed or poor and monitored the growth of their children from birth till age ten.

Through questionnaires, mothers provided information about their chidlren's food habits, including the amount of food they normally consumed and the types of foods they liked. Later, the children underwent tests that analysed their food choices.

Results showed that alterations in a gene that control the activity of dopamine, a chemical messenger that plays a major role in food choices, contributed widely to obesity. The gene alterations were more common in girls than boys. "We found that a variation in a gene that regulates the activity of dopamine, a major neurotransmitter that regulates the individual's response to tasty food, predicted the amount of 'comfort' foods-highly palatable foods such as ice cream, candy or calorie-laden snacks-selected and eaten by the children", Dr Patricia Silveira, from McGill University, explained. "This effect was especially important for girls who we found carried the genetic allele that decreases dopamine function."

Researcher Meaney added, "Our research indicates that genetics and emotional well-being combine to drive consumption of foods that promote obesity."

The study has been published in the journal Appetite.

These findings come at a time when childhood obesity has become a growing concern across the world. A 2011 World Health Organization (WHO) report showed that more than 40 million children aged below five were overweight. According to the Centers for Disease Control and Prevention (CDC)  in the US, obese children are at a higher risk of developing cardiovascular diseases like high blood pressure, cholesterol, prediabetes, bone and joint problems, sleep apnea, social and psychological problems like stigmatization and poor self-esteem.