Over 50% of the Canadian population is either overweight or obese, and these conditions cost the Canadian economy approximately $7 billion dollars each year. There have been countless mechanisms proposed to explain the obesity epidemic, but what about genetics? How much of a role does genetic make-up play for the risk of obesity?
The genetic code is basically a blueprint of how your body is built. It’s the framework. But it’s the interaction between genes and lifestyle environment that make the house a home. It’s the environment that paints the rooms, picks the finishes and gives the blueprint its form.
Obesity risk is two to eight times higher for a person with a family history of obesity. At first glance, it seems obvious that an individual’s genetic makeup will play a significant role. However, there are many cases where a child is afflicted with obesity without family history and thus presumably no genetic predisposition. In addition, identical twins, who carry the exact same genetic code, do not always share obesity. The fact that one identical twin can be obese and the other lean de facto divorces obesity from the genetic code. However, there is no doubt that genetics can increase the risk for obesity.
The most common obesity-associated gene is the FTO gene. This specific gene has surfaced in multiple studies where scientists have compared obese individuals with lean individuals and observed genetic differences. Since the identification of this link, scientists, including David Meyre from McMaster University, have found that exercise interventions dramatically reduce obesity in individuals with FTO variants. In Meyre’s study, he examined data from 17,400 people from six ethnic groups who were recruited from 17 countries and followed for more than three years. His results demonstrated that even though individuals may carry a genetic risk factor for obesity (FTO variant), the environmental interaction (exercise) overrides the genetic predisposition.
“This provides a message of hope for people with obesity predisposing genes that they can do something about it.” says Meyre.
In other words, these findings are empowering for individuals with the FTO variant because they highlight that a person’s choices, not genetics, are in the driver’s seat for obesity.
Two of the reasons why I think it’s important to highlight that it’s possible to overcome genetic predisposition are: 1) Behavioural interventions to alter lifestyle choices are going to be the backbone of our campaign against obesity, and 2) I worry about placing a large emphasis on genetic risk factors.
To explain the 1st point; in cases of severe obesity, bariatric surgery is recommended and shows impressive efficacy. However, it is not realistic to perform surgery on millions of people. The next line of defence is pharmaceutical intervention. There are currently two anti-obesity drugs approved for prescription in Canada, but until a drug comes along that complements a lifestyle intervention, I hesitate to get on board. Even in patients who have undergone bariatric surgery it is the lifestyle choices following the surgery that are vital to the long-term success of the patient. Without a lifestyle shift, long term success for obesity treatment is elusive.
To explain the 2nd point; as a thought experiment, let’s say an individual arrives at a doctor’s office who is moderately overweight and is looking to improve their health. The doctor orders a genetic test to screen for an FTO variant to find out if the individual carries a genetic risk factor for obesity. In this situation, it may be beneficial to find out if the FTO variant is present and this individual will be advised to monitor their weight closely (as they carry predisposition) and perhaps exercise is strongly recommended.
The worrisome part for me is if an individual is pre-screened for obesity risk (say, as a child) and then told they will need to be careful with their weight for the rest of their lives based on genetic risk factors. People with the FTO variant do not always have obesity, the same as identical twins do not always share obesity. Genes do not dictate destiny. The individuals being pre-screened may never develop obesity yet spend their entire lives fearing it based on a risk factor naturally overcome by a healthy lifestyle. Furthermore, living in fear of obesity may put the individual at risk for psychological conditions far worse than obesity.
by Brennan Smith, PhD
