According to a new study from University College London, families that eat more fruits and vegetables, watch less TV and have a healthy lifestyle can halve the genetic risk of childhood obesity.

People with the obesity gene are more likely to be obese than others. Fraternal twins have 50% of the same genes, while identical twins have 100% of the same genes, so their genetic obesity risk should be comparable.

Scientists from university college London followed the twins from July to October 2013 and found that the environment can actually alter the effects of these obesity genes on body mass index (BMI).

When children live in households with fewer fruits and vegetables and spend more time watching TV, 86 percent of childhood obesity is due to genetic factors. However, genetic factors accounted for only 39 percent of childhood obesity when families ate healthier meals and participated in physical activity for longer.

Dr Stephanie Schrempft, of university college London, said: "this finding supports the theory proposed by our team that genetic predisposition to obesity is highest when individuals live in an obesity-prone environment that encourages overconsumption and low physical activity. In other words, obesity genes are like guns, the environment pulls the trigger.

Dr Stephenie said the similarity in bmi between the two sets of twins in a low-risk family setting suggested that a healthy family setting could overcome genetic factors.

Obesity rates among U.S. children have tripled since the 1970s, affecting one in five children in the United States, according to the CDC. Childhood obesity has overtaken drug use and smoking as the number one health concern for American parents.

Currently, the annual medical cost of obesity-related diseases is a staggering $19.2 billion, accounting for almost 21 percent of the annual medical expenditure in the United States. The direct medical cost of childhood obesity alone is $14 billion.