How Much of a Pull Do Your Genetics Have on Your Weight?

There are many factors at play when it comes to your weight, and genetics is certainly one of them. Every person's body responds differently to food and exercise, and there's some truth to the notion that obesity is hereditary.

But what runs in your family may not necessarily be your fate. How your genetics affect your weight is only one piece of the puzzle.

If it seems like some people can eat pizza for breakfast while others gain weight just from looking at sugar, that's because, well, everyone is different — thanks in part to genes.

"We inherit all kinds of traits, such as hair and eye color, height and also body type," Keith-Thomas Ayoob, EdD, RD, clinical professor at Albert Einstein College of Medicine, tells LIVESTRONG.com. "If two people both have what might be called a 'stocky frame,' their kids are probably not going to have frames that are long and lanky."

Like other traits, there's no singular gene connected to weight. In fact, according to Harvard Health Publishing, more than 400 genes are involved in contributing to the disease of obesity.

And while we're not sure exactly how they work, there's definitely a connection between genes and weight. A November 2017 study in the ‌International Journal of Obesity,‌ for example, found that people with a higher genetic risk of obesity tended to gain more weight from age 20 on than those without this risk.

And on the flip side, a May 2020 study in ‌Cell‌ found there may be a specific gene linked to thinness. Researchers used a database including more than 47,000 people to compare the DNA of thin and "normal"-weight individuals and discovered genetic variants unique to thin individuals. More research needs to be done in this area, though, before we can say for sure.

What we do know: Our genes form the basis for our body's signal and response system, which guides food intake, according to the Centers for Disease Control and Prevention (CDC).

One hypothesis is that our bodies are primed to protect us against weight loss because energy, stored in fat, is crucial to survival. So the same genes that helped our ancestors survive food scarcity are still working to protect us, even though most of us have all the food we need and then some.

While most research has focused on how genetic risk affects obesity, more recent research has taken an in-depth look at the links between genetics, obesity and body mass index (BMI) over time. And while BMI has its limitations, it is used in research as an indirect way of assessing obesity-associated health risk.

Studies on twins are especially common in this area. One February 2012 study in ‌PLOS One‌ looked at how genetics and environment affected the weight, height and BMI of 12,000 twin pairs from three continents. The study followed the twins from birth to 19 years old.

The researchers noted that past studies had found weight to be between 50 and 90 percent genetic, but these estimates varied widely based on differences in study types, populations and ages targeted. Their review concluded that weight is about 50 percent genetic.

Another study looked more closely at adults and the effect of genetics on weight over time.

The January 2020 study in ‌JAMA Cardiology‌ combed through data on more than 2,500 adults from 1985 to 2010. Using a score based on each participant's DNA, they calculated the genetic risk of obesity for each person and compared it to measurements taken over the course of the 25-year study period. They also monitored each person's BMI over time.

"You may need to adjust your goals to take into account what your body can do [but] lifestyle and your eating style are major players in the obesity war — perhaps the main players because they're the only ones over which you can have some control."

Their analysis showed that BMI in young adulthood explained about 52 percent of a person's BMI 25 years later, while genetics explained only about 14 percent. In the end, they concluded that fitness and BMI over time were better indicators of obesity risk than genetics.

Ayoob agrees that having a family history of obesity does not mean you have no control over your BMI.

"It means you may need to adjust your goals to take into account what your body can do and what you should expect," he says. "Lifestyle and your eating style are major players in the obesity war — perhaps the main players because they're the only ones over which you can have some control."

The bottom line? Genes play a role, yes, but lifestyle — aka the diet and activity choices you make every day — is the best determining factor when it comes to the number on the scale, your BMI and your overall health.

And if your lifestyle isn't the healthiest, it's worth it to make some improvements: The excess fat associated with obesity puts people at risk for other serious conditions, such as cardiovascular disease and stroke.

Regardless of your genetic risk, here are some suggestions from the experts to get started with healthy lifestyle changes:

People with a genetic propensity toward obesity can lower their percentage of body fat by raising their metabolism, Robert Herbst, a personal trainer specializing in weight loss, tells LIVESTRONG.com.

To do this effectively, he highly recommends regular weightlifting.

"You should perform compound movements such as squats, lunges, bench press and deadlifts. These cause your metabolism to be elevated for 48 to 72 hours afterward as your body repairs muscle fibers that were broken down during the exercise and builds additional muscle in anticipation of greater loads in the future," he says.

Because muscle is more metabolically active than fat, building more of it helps your body burn more calories, even at rest.

Obesity is diagnosed when your body fat levels are much higher than the healthy range. At the very basic level, too much body fat occurs when more calories come in than go out. So it makes perfect sense to take stock of how and what you eat when confronting obesity.

"Genetics aside, look at the eating habits you grew up with. Are they compatible with having a healthy weight?" Ayoob asks.

A healthy, balanced diet where no food group is restricted is the best approach, he says.

Herbst recommends focusing on whole foods (think: fruits, vegetables and whole grains) and limiting empty-calorie foods like soda, chips and sweets.

As part of a healthy eating plan, the National Heart, Lung, and Blood Institute emphasizes staying within your daily calorie goal for weight loss and controlling portion sizes.

An important part of the equation when making healthy lifestyle changes is making sure those changes are maintainable. Ayoob recommends setting realistic goals and starting off slow.

"Weight loss that is slow and steady, not fast and furious, will win this race," he says. "Give yourself a year. The year will pass anyway, so it's a matter of it passing with progress or just keeping the status quo."

In that time, aim to be purposefully active most days, even if that means just brisk walking, for at least 30 minutes.

He advises his own patients to engage in 30 to 60 minutes of physical activity five or more days a week, with walking being the most common activity.

This is in line with the U.S. Department of Health & Human Services' Physical Activity Guidelines for Americans, which recommend adults do at least 150 minutes of moderate-intensity aerobic physical activity each week along with muscle-strengthening activities at least two days.

A February 2022 overview in the ‌International Journal of Molecular Sciences‌ notes that eating and exercise patterns aren't the only lifestyle contributors to obesity. Indeed, budding research shows that sleep deprivation may trigger changes in the body that contribute to obesity and metabolic diseases.

Other research, too, has shown that one of the side effects of a lack of sleep may be weight gain.

With that in mind, aim for seven to nine hours of sleep each night, and take steps to make sure your time between the sheets is high-quality. That means practicing good sleep hygiene, including going to bed and waking up at the same time each day; making sure your bedroom is cool, dark and quiet; shutting off screens an hour or two before bed; and avoiding caffeine in the afternoon and alcohol a few hours before bedtime.