Is Obesity Genetic or Environmental? Get All the Details

Key Takeaways:

• Both environment and genetics can influence a person’s obesity risk, with some genes affecting appetite, metabolism, fat storage, and food preferences.

• Rare single-gene mutations can cause obesity, but most obesity is shaped by many genes interacting, in addition to lifestyle factors.

• Your genetic makeup alone doesn’t determine your fate. Diet, physical activity, sleep, and stress management can all play into outcomes.

• Personalized strategies, including tailored lifestyle changes and medical support through prescriptions like GLP-1, can help manage weight effectively — even in people who have a genetic predisposition.
  

While lifestyle choices, including diet and activity level, play an important role in a person’s risk of obesity, genetics can also shape natural tendencies toward weight gain or loss. In fact, genes affect everything from how your body stores fat to how hungry you feel and how efficiently you burn calories.

Understanding how these factors interact with the environment and daily habits can help people take realistic, personalized steps to manage weight and improve overall health. Ahead, we’ll break down what science says about the genetic causes of obesity, how those genes work, and what you can do to support your health, no matter your genetic makeup.

Genetic factors play a major role in shaping body weight, body mass index (BMI), and more.

The genetics of obesity can vary widely, from rare, single-gene mutations that cause severe obesity to more common forms that are the result of hundreds of genetic variants and other obesity-associated conditions.

Let’s take a closer look at some types and categories of genetic obesity below:

Syndromic Obesity: Co-Occurring Disorders

Syndromic obesity refers to conditions where excessive weight gain occurs alongside other medical, developmental, or physical features. These syndromes often involve intellectual disabilities, developmental delays, or distinctive physical traits.

Obesity is just one part of a broader picture. Some examples include:

• Prader-Willi syndrome is a genetic disorder causing insatiable appetite, low muscle tone, and developmental delays, leading to early-onset obesity (around age 4 - 8).

• Bardet-Biedl syndrome is a rare genetic condition affecting multiple organ systems, often characterized by obesity, vision problems, kidney abnormalities, and extra fingers or toes. It also has an early onset.

• Down syndrome is a genetic disorder caused by an extra copy (full or partial) of chromosome 21, causing developmental delays, intellectual disability, and distinctive physical features. People with Down syndrome have a higher prevalence of obesity compared to the general population, often due to a combination of genetic and lifestyle factors.

Monogenic Obesity: Single Gene Variants

Monogenic obesity refers to rare, heritable conditions caused by mutations in a single gene. These mutations usually appear early in life and are marked by intense hunger (hyperphagia) and fast weight gain.

Most of the affected genes in cases of monogenic obesity help your brain regulate appetite and energy balance. Key genes associated with monogenic obesity include:

• Leptin gene (LEP). Leptin is a hormone made by fat cells that signals to your brain when you’re full. Mutations in LEP can cause leptin deficiency, leading to constant hunger and early-onset obesity.

• Leptin receptor gene (LEPR). Abnormalities in this gene prevent the brain from receiving leptin’s “I’m full” signal, causing similar symptoms to those in LEP mutations.

• Pro-opiomelanocortin gene (POMC): This gene produces neuropeptides that regulate appetite. Mutations in it can cause intense hunger, early obesity, and adrenal issues.

• Melanocortin 4 receptor gene (MC4R): This is the most common single-gene cause of severe early obesity. When MC4R doesn’t work properly, appetite and food intake increase.

Some single-gene conditions are treatable. For example, leptin replacement therapy can help people with LEP deficiency, and MC4 receptor agonists (injectable medications) may help to treat an MC4R dysfunction.

Polygenic Obesity: Multiple Gene Interactions

Most obesity is polygenic, meaning it arises from the combined effects of many genetic variations. These genetic factors interact with lifestyle and environmental influences (like diet, activity, and stress) to shape overall risk.

Large-scale genome-wide association studies (GWAS) have identified hundreds of genetic variants linked to BMI and obesity. One of the most well-studied is the FTO gene, which influences appetite and food intake. People with certain FTO variants tend to have higher BMIs and greater obesity risk.

Some key components involved in polygenic interactions include:

• How your brain senses hunger and satiety (fullness)

• How your body develops and stores adipose tissues (fat)

• How your body processes sugars and fats

• How your body burns calories

An Overview: Genetic Forms of Obesity

Appetite Regulation and Satiety

One of the clearest ways genes affect body weight is through appetite control. Variations in genes that regulate hormones and neurotransmitters can make some people feel hungrier or less satisfied after eating.

Some examples of genetic issues that can impact appetite and satiety include:

• Leptin and ghrelin sensitivities. Genetic predispositions can affect how sensitive you are to hormones like leptin and ghrelin, which tell your body when to stop or start eating. When these signals don’t register efficiently, it’s easier to overeat.

• Neuropeptide differences. Some people are more sensitive to appetite-stimulating chemical messengers in the hypothalamus, which heighten the drive to eat.

• MC4R function. Variations in the MC4R gene can also blunt fullness signals, making some people more prone to overeating.

These differences don’t make overeating an inevitability, but can help to explain why hunger may feel more intense for some individuals than others.

Energy Expenditure and Metabolism

Genes can influence how efficiently your body burns energy at rest and during activity. Here’s how:

• Basal metabolic rate (BMR). Older studies suggest that genetic variations affect your natural calorie-burning rate, meaning two people of similar size may burn calories at different speeds.

• Thermogenesis. Some people have genes that can make their bodies less efficient at converting calories to heat, leading to fewer calories burned overall.

• Physical activity level and motivation. Genetics may play a role in how your body and brain respond to exercise — influencing how enjoyable activity feels and how much effort is required. Some research also links genes related to dopamine and mood to differences in activity levels. For example, heritable mental health conditions like depression or attention-deficit/hyperactivity disorder can indirectly affect lifestyle behaviors tied to obesity risk.

Together, these factors can make weight gain easier for some people than others, based solely on their genetics.

Fat Storage and Distribution

Research shows that in addition to genes influencing how much fat you store, they may also play into how many fat cells you form and where your body chooses to store fat (for example, around your belly versus under your skin).

Food Preferences and Cravings

Genes can influence:

• Taste sensitivities. Variants in certain genes can affect how bitter or sweet foods taste, shaping preferences for vegetables, sweets, or fatty foods.

• Reward pathways. Differences in dopamine-related genes can guide how rewarding food feels, making some people more prone to craving high-calorie or sugary foods.

• Nutrient responses. Genetic variations can alter how your body detects and responds to carbs, fats, or proteins, subtly guiding your susceptibility to cravings.

Understanding your biological tendencies can empower you to make more personalized, sustainable choices.

Twin studies show that while genetics can have a strong association with body weight in childhood obesity, genes don’t act alone. Family habits, diet, activity levels, and the broader environment all play a role.

Below, we’ll look at some ways your lifestyle and genetic makeup can work together to affect obesity.

The Obesogenic Environment

The term “obesogenic environment” describes the combination of easy access to high-calorie foods and our modern culture that encourages sitting more than moving.

Two particularly important points include:

• Unhealthy food availability and food deserts. Many communities in the U.S. are surrounded by inexpensive and tasty foods that also tend to be highly processed and calorie-dense. Living in such food deserts — places where it’s hard to access fresh, minimally processed nutrition — makes it extra hard to maintain a healthy weight.

• Less physical activity. Evolving technology and changes in how we work and relax mean fewer natural opportunities to move. This can play out in a few ways. For example, those who are genetically less motivated to be active may find it even harder to build regular exercise into daily life.

Put simply, when the environment promotes overeating, poor nutrition, and inactivity, genetic tendencies toward weight gain are more likely to show up.

Dietary Patterns and Genetic Predisposition

Your genes can also influence how your body responds to different diets. 

For example, people with certain variants of the FTO gene may gain more weight when consuming high-fat diets than those without the variant. Other variations in genes tied to insulin signaling may determine how well someone responds to diets, like a low-carb diet.

This suggests that personalized nutrition based on genetic insights could be more helpful.

Physical Activity and Genetic Influence

Exercise is key for managing weight, but your genes can also play a role in how your body and brain respond to physical activity:

• Some people naturally see bigger benefits from exercise, like faster metabolism or more fat loss, while others may progress more slowly — even when doing the same activities and exerting the same effort.

• Genes also play a role in how much you enjoy physical activity. So if workouts feel harder or less rewarding, it’s not necessarily a matter of willpower.

Still, physical activity remains one of the most powerful tools for offsetting genetic risk and supporting overall health.

How a Person’s Environment Can Reshape Genes

Epigenetics — lifestyle variables that can alter DNA transcription and gene expression — shows that while your genes set the stage, your environment and behaviors can change how your genes “act.”

Specifically, nutrition during pregnancy and childhood can shape your metabolism for life. For instance, too little or too much nutrition in the womb can affect genes that control appetite and energy use, which may increase obesity risk later.

Diet, exercise, sleep, and stress can influence genes in adulthood, too. Healthy habits can “switch on” genes that help metabolism and “switch off” those linked to fat storage and inflammation.

The takeaway? Everyday choices can influence how your body expresses your genes over time. “Your genes aren’t your destiny,” says Hims & Hers Medical Advisor Lynn Marie Morski, MD, JD. “While your DNA stays the same, everyday choices — like how you eat, move, sleep, and manage stress — can influence how those genes are turned on or off over time.”

Even if your genes make you more likely to gain weight, losing or managing weight is still possible. Your body might respond differently to foods, exercise, or treatments, but knowing this can help you take a smarter, more personalized approach. Think of your genes as a guide, not a limitation.

1. Take a Holistic Approach

With or without a genetic predisposition for obesity, the fundamentals still matter — and consistency can better support your biology. A holistic, sustainable weight management plan includes:

• Dietary changes. Focus on nutrient-dense, whole foods and mindful eating habits rather than rigid restrictions. Understanding how your genes affect macronutrient processing can guide smarter, not stricter, choices.

• Regular movement. Combine cardio and strength training. Also, focus on activities you genuinely enjoy in order to help you stay consistent.

• Emotional well-being. Stress, sleep, and emotional eating play major roles in weight management. Strategies like stress-reduction techniques, better sleep hygiene, and mindful coping can make a measurable difference.

2. Consider Tailored Lifestyle Interventions

Research in precision nutrition and personalized medicine shows that lifestyle interventions work best when they’re tailored to your body. Some avenues to explore:

• Genetic testing for insight. While genetic testing isn’t usually used to diagnose obesity, it can highlight tendencies like how your body stores fat, processes carbs, or controls appetite. This can guide more targeted nutrition and exercise choices.

• Phenotypic assessments. Even without genetic testing, working with a specialist to understand your phenotype — your measurable traits, like body fat to muscle ratio, metabolic rate, and eating patterns — can help identify strategies that actually work for you.

It’s important to identify habits that fit your unique body and lifestyle.

3. Explore Medical Support

If you’ve made consistent and targeted lifestyle changes but still struggle to manage your weight, talking with a healthcare provider can be a turning point. They can rule out underlying conditions and chat through prescription medications for managing obesity and overweight.

For example, injectable GLP-1s may reduce feelings of hunger to help you lower your calorie intake and slow the movement of food from the stomach to the small intestine. This can help you feel fuller longer.

Some options include:

• Semaglutide (Ozempic^®, Wegovy^®)

• Compounded semaglutide*

• Tirzepatide (Mounjaro^®, Zepbound^®)

• Liraglutide (Saxenda^®, Victoza^®)

Oral weight loss medications are also available, including:

• Naltrexone

• Metformin

• Topiramate

• Bupropion

Hers offers access to both injectable and oral weight loss medications, and both can be effective options.

Hers customers using oral medication kits — paired with healthy lifestyle changes — report losing an average of 15 pounds or 8.4 percent of their body weight in the first six months.** As for medications like GLP-1s, clinical trials on Wegovy^® showed that participants lost an average of 20 percent of their body weight after 68 weeks.

*Compounded drug products are not approved or evaluated for safety, effectiveness, or quality by the Food and Drug Administration (FDA). Prescription required.

**Based on self-reported data as of March 2025 from approximately 1,172 Hers customers on a personalized treatment plan including oral medication kits, along with a reduced-calorie diet and exercise. Customers reported their weight at their initial medical consultation and again at their check-in about 6 months later.

Obesity is, in part, genetic. But the answer isn’t a simple yes or no. While genes can guide appetite, metabolism, fat storage, and even food preferences, they don’t determine your fate.

Another way to look at it: Genetics may set the foundation, but environment, lifestyle, and mindset can also shape the outcome. So with the right combination of personalized strategies, medical support, and mindset, meaningful, lasting progress to support a healthy lifestyle is absolutely achievable.

If you’re curious about whether Hers could be right for you, take our online weight loss assessment to learn more about your treatment options.

Is obesity genetic or environmental?

Both. Genetics play a role in appetite, metabolism, and how your body stores fat — but environment and lifestyle play powerful roles, too. Our modern environment, with its abundance of high-calorie foods and sedentary routines, can amplify genetic risks. Put simply, obesity results from a complex interaction between your inherited traits and the world in which you live.

Can you get tested for genetic obesity?

Yes, but testing is mostly used for rare single-gene (monogenic) obesity. These tests examine mutations in specific genes involved in appetite, hunger, cravings, and other components of weight gain or factors of obesity. For polygenic obesity — which is more common and involves many genes— tests can estimate your genetic predisposition but can’t predict outcomes or provide a definitive diagnosis. A healthcare professional can help interpret results and guide next steps.

What is the obesity gene called?

There is no single “obesity gene.” Obesity usually results from multiple genes interacting with lifestyle and environment. The most studied gene is FTO, which is linked to a higher BMI and a greater risk of obesity. Rare single-gene forms involve genes like LEP, LEPR, POMC, and MC4R, which regulate appetite and energy balance.

Is there a cure for genetic obesity?

Because you can’t change your genes, there’s no cure for genetic obesity, but you can manage the effects. Common interventions include lifestyle strategies (diet, exercise), behavioral support, and sometimes medical treatments, such as GLP-1 medications. These approaches can help people lose weight and improve health, even if genetic risk remains.

Ozempic^® and Wegovy^® are registered trademarks of Novo Nordisk A/S. Hims, Inc. is not affiliated with or endorsed by Novo Nordisk A/S.