Is obesity genetic?

As we talked about here, it's impossible to identify a specific reason why a person gains weight and develops obesity. However, we do know that genetics is one of the possible causes of obesity. Ongoing research on the relationship between genetics and obesity show that genes influence:

• How much food you tend to eat in a sitting.
• How you respond when you feel full.
• How much enjoyment you get from certain types of food.
• How much energy you need to run basic body functions (such as breathing or circulating blood in your body).
• How and where excess calories are stored as fat in your body.

Just as genes can determine the colour of your eyes, genes can also determine your tendency to put on weight or develop obesity.
 

Genes play a central role in obesity. But if genetics and obesity are closely related, why does it seem like more people are affected by obesity now? There were very few people with obesity a hundred years ago - so is obesity really genetic?

Our genes haven't changed much over the last hundred years. In fact, they haven't really changed over the past 50,000 years. What has changed is our environment. 

As the geneticist Francis Collins puts it, “Genetics loads the gun and environment pulls the trigger.” That means that genetic factors and environmental factors may not work on their own, but interact with each other to produce a result. 

We now live in a different environment compared to people who lived a hundred or so years ago. We live with different types of stress, food, and technology. The modern world interacts with our genes and obesity is part of the result.

Professor Joseph Proietto, a researcher and clinician specialising in obesity, explains genetics and obesity by asking us to think about two pots. They are different sizes: one pot holds 5 litres while the other pot holds 50 litres. The pots stand in the rain overnight and in the morning, both pots are full of water.

When you look at both pots, you can see that the larger pot holds more water than the smaller pot. Professor Proietto explains that this is because the bigger pot was made to hold more water. “In other words, you need both your genetic make-up (how the pot was made) and the environment (the rain) to develop obesity,” he says.
 

Some of the first clues of a link between genetics and obesity came from researchers from the University of Michigan. In 1952, they conducted a study with 81 pairs of twins where they measured the twins in many ways, including foot length, forearm length, and even nose height.

The measurements enabled the researchers to figure out the likelihood that these different traits were inherited from the twins' parents. This is called heritability. Out of all the traits that the researchers measured, they found that the ones with the highest heritability rate were body weight and waist circumference. Many studies comparing twins have been done since. Researchers found that whether they were raised together or apart, identical twins were similar in weight.

This shows that your environment, how you live, and what you do are not the only things that influence your body weight. Instead, genes have a lot of power in determining how much you weigh. Together, these findings provide indisputable evidence that genetics and obesity are closely related. Some evidence suggests obesity is between 40% to 70% determined by genetics. This means that the genes you inherit from your parents may increase your risk of developing obesity.
 

The more you know about genetics and obesity, the more informed you are when making decisions about managing your weight. For example, you can be more aware of the different triggers in your environment that can make you eat more or increase the risk of developing obesity.

It's also worthwhile to consider that because of our individual genetics and obesity factors, we may respond differently to different types of treatment. Strategies and treatments that work for one person may not work for another. That’s why each person needs an individual approach to managing weight.