Obesity has developed into a worldwide epidemic that affects the health of millions of people in every country on the planet. Although the reasons for obesity are complicated and diverse, many individuals question if heredity plays a part in the development of this problem.
Let’s examine the evidence surrounding the relationship between genetics and obesity.
What is Obesity?
Obesity is defined as the excessive accumulation of fat that leads to a weight that is more than what is considered healthy for a particular height and has adverse effects on one’s health. While there are many ways to measure or estimate body fat percentages, we will focus on just two.
Fat can be measured with a metric called body mass index (BMI). BMI is a measure of body fat that takes into account both height and weight. A BMI of 30 or higher is the definition of obesity.
It’s very important to include height when discussing weight. For example:
- If you tell me you’re 250 pounds, that doesn’t tell me anything.
- If you’re 4’ 8” and 250 pounds, your BMI is 56. You fit the definition of obesity.
- If you’re 6’ 8” and 250 pounds, you have the measurements of Lebron James. You don’t have a weight problem.
Of course, BMI is a crude tool and doesn’t tell the whole story of a person’s health. For instance, Hall of Famer Mike Singletary was 5’ 11” and weighed 232 pounds when he played for the Chicago Bears. His BMI was 32, but he was not obese. Athletes and very muscular people tend to be penalized by the BMI scale.
Dual energy x-ray absorptiometry (DEXA) is the gold standard when it comes to determining body fat percentage. A DEXA scan assesses your body composition by estimating the amount of fat tissue you have. We have a DEXA scanner in my office that we use to scan patients before surgery and at intervals after surgery.
The problem with DEXA, though, is that most people don’t have convenient access to this scanner! That’s why the majority of the world uses BMI instead.
What Role Does Genetics Play in the Development of Obesity?
Some debates will never be totally settled.
Which college football conference is best?
Was there a shooter on the grassy knoll?
Who is D.B. Cooper?
Is nature or nurture predominant in determining physical traits?
While I won’t presume to solve the assassination of JFK in the next few paragraphs, science does have something to say about the nature vs. nurture debate.
What Does the Data Say?
The data shows that nature and nurture are interdependent, tightly dovetailed parameters that play an integral part in the development of our physical and behavioral traits. As it relates to obesity, though, it would appear that nature has a lot to say on the matter.
Research on identical twins who were brought up in different households has produced some fascinating results. Consider:
- If environment (“nurture”) is the more significant determinant, then the rates of obesity among these twins should be very different from one another.
- If genetics (“nature”) is the stronger influence, there should be similar rates of obesity between the twins because they are genetically identical.
Studies involving identical twins separated at birth conclude that genetics plays a substantial role in obesity. In 1990, the New England Journal of Medicine (NEJM) published an article that analyzed 93 sets of identical twins raised apart, 154 sets of identical twins raised together, 218 sets of fraternal twins raised apart, and 208 sets of fraternal twins raised together. This large study concluded that “genetic influences on body-mass index are substantial, whereas the childhood environment has little or no influence.”
Studies of adopted children also conclude that your chromosomes play a huge role in obesity. Another study published in the NEJM examined 540 adoptees, analyzed their weight classes, then compared them to their biological and adopted parents. Amazingly, the adopted children were much more similar in body structure to their biological parents than to their adoptive parents. So striking was the support for this that the researchers concluded that “genetic influences have an important role in determining human fatness in adults, whereas the family environment alone has no apparent effect.”
Recent genomic and epidemiologic studies have concluded that—you guessed it—at least some of obesity is, unquestionably, inheritable. According to a 2007 study that analyzed the data contained in genetic mapping and then harmonized this with genetic epidemiologic research, somewhere between 6% and 85% of obesity is inheritable. That’s a wide range, to be sure, but the researchers felt that this was a reflection of the differences of inheritability for different populations.
Scientists have even been able to isolate so-called “fat genes.” One of the most well-known genes associated with obesity is the FTO gene. There is evidence to suggest that the risk of obesity is increased by as much as 70% because of this gene. People who carry the FTO gene tend to have higher amounts of body fat and a greater propensity for putting on excess weight. Brain scans have shown that patients with this gene seem to not respond to conventional satiety cues, and it may cause people to respond to food in a more intense fashion. In addition, there is a possibility that they are more prone to binge eating and that they have a greater risk of developing type 2 diabetes and Alzheimer’s disease.
The MC4R gene has also been linked to obesity. It’s estimated that mutations in this gene, which are found in around 22% of the population, are responsible for 6% to 8% of all cases of obesity. Because it causes an increase in appetite and a decrease in satiety, the MC4R gene is associated with an increased risk of weight gain and binge eating.
Suffice to say, genetics plays a more-than-casual role in obesity.
Is DNA Destiny?
If you’re getting a shiver down your spine because your family genetics resemble that of Sherman Klump from The Nutty Professor, remember that DNA is not necessarily destiny.
There’s a saying: “Genetics loads the gun, but environment pulls the trigger.” In other words, your chromosomes determine a preset range, but your environment and decisions pinpoint your landing spot for your observable characteristics.
A classic example? Height.
I am 6’ 2”. My genes say I will never be a Shaquille O’Neal, but my God-given range may have been from 5’ 8” to 6’ 3”. My healthy upbringing, good nutrition, and safe environment dictated that I was able to nearly reach my full genetic potential. Choices and good fortune alike had a positive influence on my dictated genetics.
Genetics is only a piece of the puzzle when it comes to obesity. By making healthy lifestyle choices, such as eating a balanced diet, engaging in physical activity, and avoiding habits that can contribute to weight gain, individuals can reduce their risk of obesity, even if they have a genetic predisposition to the condition.
Talk to Your Doctor About Obesity
Genetics affects obesity, but it’s not the only factor at play. It’s important to consider the interplay of genetic, behavioral, and environmental factors. While genetics can increase an individual’s risk of developing obesity, healthy lifestyle choices—such as a balanced diet and regular physical activity—can reduce that risk significantly.
If you are concerned with your body’s fat composition, talk to your primary care physician (PCP) about starting a physician-supervised diet, exercise, and behavior modification weight loss plan. If you are still having challenges with your weight and obesity-related medical conditions, I would strongly encourage you to reach out to the Bariatric and Metabolic Institute at Arkansas Heart Hospital.