How Much Do Your Genes Really Impact Your Weight?

Your lifestyle habits — such as what you eat or how much you move — aren’t the only things that dictate your weight. Your genes play a role, too. 

But how much is your weight actually determined by genetics? Past research indicates that when it comes to what influences your weight, the split between your genes and your lifestyle is about 50/50. (1)

While you can’t change your genes, you can change your lifestyle habits. So if you struggle with your weight, read on to learn more about how your genes impact the number on the scale — and what you can do about it.

The Genetics and Weight Gain Connection

Genetics may be one factor in weight gain. “There’s for sure a genetic component to obesity. Children of obese parents are more likely to grow up to be obese themselves,” says Charlie Seltzer, MD, who is board certified in obesity medicine and internal medicine. 

In fact, having one parent with an obese body mass index (BMI) increases a child’s risk of obesity by 50 percent; if both parents are categorized as obese, the risk increases to 80 percent. (2) This isn’t fully due to genetics, however; the household you grow up in also impacts what you eat and other lifestyle behaviors.

That said, there are a few specific genes that can contribute to obesity on their own, says Lydia Alexander, MD, president-elect of the Obesity Medicine Association. One is the melanocortin-4 receptor (MC4R), which regulates appetite and the body’s energy balance. Research suggests that about 7 percent of the population has an MC4R gene mutation. (3) But having one of these mutations doesn’t mean you develop obesity; in fact, some of these mutations are protective against obesity. MC4R gene mutations are believed to play a role in 2 to 3 percent of child and adult obesity, additional research indicates. (4) 

Another common gene linked to increased BMI and fat mass is the FTO gene. (5) Dr. Alexander points out that this gene is associated with an increased appetite and decreased satiety after eating, which can then be a risk for overeating and, over time, obesity.

Notably, these are just a couple of examples. There’s still a lot that experts don’t know about how much genetic factors influence your weight, according to Alexander, who is also the chief medical officer for Enara Health, a healthcare platform using genetic testing to optimize diet planning. What may be helpful, says Alexander, is that you can get genetic testing for some of the genes linked to obesity, which can help doctors understand if you’re predisposed to potential weight problems or even help inform the right composition of your diet. 

How Lifestyle Impacts Genetics and Weight

While certain genes may raise your risk, your lifestyle plays a huge part in whether or not you gain excess fat that puts you in either an overweight or obese BMI category. “When you add in environmental stimuli — stress, poor sleep, sedentary behavior, living in a food desert where only processed foods are accessible — [it] creates an interplay that can tip you over the edge into obesity,” says Alexander.

How you were raised also makes a difference. You may have been a child decades ago, but that influence still matters now, too. “Genetics [are] a factor in how we interact with our environment and how the environment affects us,” explains Alexander. For instance, if you have obesogenic genes, but you were exposed to a healthy diet and lifestyle growing up, you’re less likely to develop obesity as you get older, Alexander says. Certain life stages — such as puberty, pregnancy, and menopause — can also act as triggers for lasting weight gain.

The Role of Calorie Tracking

Your genes may make it harder to lose weight, but weight loss is possible for anyone, says Dr. Seltzer. “You can’t fight your genes. But this doesn’t change how you have to approach weight loss,” he adds.

It involves eating fewer calories than you burn, which can be more difficult for some folks. “Those who have a genetic propensity to obesity need a larger calorie deficiency than you’d think they need,” says Seltzer.

To figure out your calorie sweet spot, Seltzer recommends weighing yourself daily for two weeks as well as carefully tracking everything you eat “honestly, accurately, and completely.” So, for example, if your average calorie intake over those two weeks is 2,400 calories a day, then reduce that by 10 percent, says Seltzer.

But if your genes are working against you, you may have to decrease calorie intake further. First, though, take that honest accounting of your calorie intake. “We all eat more than we think we do,” says Seltzer.

More Ways to Lose Weight Regardless of Your Genes

A variety of dietary approaches can work for weight loss; there’s no “perfect” diet. (6) Creating a calorie deficit is the most important thing, but there are numerous ways to do that, including eating low-fat or low-carb, following an intermittent fasting schedule, or going on a Mediterranean diet.

These nutritional strategies all require changes to what you eat, but weight loss specialists don’t stop the conversation there. “When we treat obesity, we think not just about genetics, but also behavior modification,” says Alexander. That includes physical activity (to reduce fat and change your body composition), stress reduction, and good-quality sleep, along with nutrition. 

Medication can also come into play. If you take medication that has weight gain as a potential side effect, you might work with your doctor to see if you can switch it. In addition, FDA-approved prescription medications for weight loss, such as GLP-1 inhibitors (one example is semaglutide), can be combined with healthy lifestyle habits. Of course, weight loss medications aren’t right for everyone, nor are they a magic bullet for weight loss. In general, talk to your doctor about which approaches might be right for you. “In most cases, obesity treatment is multifactorial,” Alexander says. 

No matter what route you take, what’s important is maintaining self-compassion throughout the journey. “We tend to think that if we only had more willpower or self-discipline, we wouldn’t have this issue. That can bring about feelings of shame and be discouraging,” Alexander says. Shame itself can fuel disordered eating and create additional stress that works against your efforts to lose weight.

“The longer you modify your habits and move toward a healthier weight, [the more] you can change your weight set point and keep it in a different position,” says Alexander. “Your genetics don’t have to dictate everything you’re doing. There are so many factors in your control.”

Editorial Sources and Fact-Checking

1. Evert AB and Franz MJ. Why Weight Loss Maintenance Is Difficult. Diabetes Spectrum. August 1, 2017.
2. Obesity. UCSF Benioff Children’s Hospitals.
3. Namjou B, Stanaway IB, Lingren T, et al. Evaluation of the MC4R gene across eMERGE network identifies many unreported obesity-associated variants. International Journal of Obesity. September 20, 2020.
4. Huvenne H, Dubern B, Clément K, et al. Rare Genetic Forms of Obesity: Clinical Approach and Current Treatments in 2016. Obesity Facts. June 1, 2016.
5. Lan N, Lu Y, Zhang Y, et al. FTO — A Common Genetic Basis for Obesity and Cancer. Frontiers in Genetics. November 16, 2020.
6. Kim JY. Optimal Diet Strategies for Weight Loss and Weight Loss Maintenance. Journal of Obesity & Metabolic Syndrome. March 30, 2021.

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