What Is the Obesity Gene Called? Understanding the FTO Gene and the Genetics of Obesity

By Natalie Hernandez, MD
Board-Certified Pediatric Endocrinologist & Metabolic and Obesity Specialist

What Is the Obesity Gene Called?

If you've searched online for "What is the obesity gene called?", you've probably come across the FTO gene. It is often referred to as the "obesity gene" because it was the first common genetic variant strongly linked to obesity and remains one of the most well-studied.

Short answer: The FTO (fat mass and obesity-associated) gene is the gene most commonly called the obesity gene. However, obesity is not caused by a single gene. Scientists have identified hundreds of genetic variants that influence appetite, metabolism, fat storage, and energy balance.

The good news is this:

Having an obesity-related gene does not mean you or your child are destined to develop obesity. Genetics may increase risk, but healthy habits, medical care, sleep, physical activity, hormones, and a child's environment all play important roles in long-term health.

Key Takeaways

• The FTO gene is the gene most commonly referred to as the "obesity gene."
• More than 300 genetic variants have been linked to obesity.
• MC4R is the most common cause of rare, inherited (monogenic) obesity in children.
• Genes can increase a child's risk for obesity, but they do not determine the future.
• A pediatric endocrinologist can help determine whether additional evaluation or genetic testing is appropriate.

What Does the FTO Gene Do?

The FTO gene helps influence how the brain regulates hunger and fullness.

Children and adults who inherit certain FTO variants may naturally:

• Feel hungry sooner after eating
• Feel less satisfied after meals
• Prefer higher-calorie foods
• Eat slightly more calories throughout the day

Interestingly, the FTO gene does not simply "slow your metabolism." Instead, researchers believe its greatest effect is on appetite regulation within the brain, particularly the hypothalamus—the body's control center for hunger and energy balance.

Each copy of a common FTO risk variant has only a modest effect on body weight. Even so, because these variants are relatively common, they have become one of the strongest genetic contributors to obesity across large populations.

Is There Really a "Fat Gene?"

Not exactly.

Although the phrase "fat gene" is popular online, it oversimplifies an incredibly complex condition.

Think of obesity like a puzzle. Genetics are one piece—but they are only one piece.

Researchers have identified hundreds of genetic regions associated with body weight. Each one contributes a small amount, and together they interact with lifestyle, nutrition, sleep, physical activity, stress, medications, hormones, and the environment.

This helps explain why:

• Two siblings can eat similar diets yet have different body types.
• One child gains weight easily while another does not.
• Some children feel hungry much more often than others.

These differences are rooted in biology, not simply willpower.

Other Important Obesity Genes

While FTO is the best-known obesity-associated gene, several others play important roles.

MC4R

The MC4R (melanocortin-4 receptor) gene helps regulate appetite and energy balance.

Unlike FTO, which modestly increases obesity risk, rare changes in MC4R can cause severe, early-onset obesity. Children with MC4R-related obesity often experience:

• Extreme hunger beginning at a young age
• Rapid weight gain during childhood
• Increased growth in some cases

MC4R mutations are the most common cause of inherited single-gene obesity in children.

LEP (Leptin)

The LEP gene produces leptin, a hormone made by fat tissue that tells the brain when the body has enough stored energy.

Rare leptin deficiency prevents this signal from reaching the brain, leading to severe hunger and rapid weight gain beginning in infancy.

LEPR (Leptin Receptor)

The LEPR gene creates the receptor that allows the brain to respond to leptin.

If the receptor does not function properly, the brain behaves as though the body is starving, even when plenty of fat is stored.

POMC

The POMC gene helps produce hormones involved in appetite regulation, adrenal function, and skin pigmentation.

Rare mutations can cause severe obesity during infancy or early childhood.

PCSK1

The PCSK1 gene helps activate multiple hormones that regulate metabolism and appetite.

Although uncommon, changes in this gene can contribute to obesity along with hormonal and digestive problems.

The Most Common Obesity Genes

Can Obesity Be Inherited?

Yes.

Research suggests that genetics account for roughly 40% to 70% of the differences in body weight between individuals.

However, inherited risk is not the same as inherited destiny.

For example, one child may naturally:

• Become hungry more often.
• Burn fewer calories while resting.
• Store calories more efficiently.
• Have stronger cravings for calorie-dense foods.

Understanding these biological differences helps remove blame and allows families to focus on strategies that actually work.

Should My Child Have Genetic Testing?

Most children with overweight or obesity do not need genetic testing.

However, testing may be appropriate if a child has:

• Severe obesity beginning before age five
• Extreme or constant hunger (hyperphagia)
• Developmental delays
• Hormonal abnormalities
• A family history suggesting a rare inherited obesity syndrome

A pediatric endocrinologist can determine whether genetic testing would provide useful information or change treatment decisions.

Genes Are Not Destiny

One of the biggest myths about obesity is that genes determine everything.

They don't.

Genes influence risk, not certainty.

Children with obesity-associated genes can absolutely improve their health through individualized care.

Treatment may include:

• Nutrition counseling
• Physical activity guidance
• Better sleep habits
• Behavioral support
• Evaluation for hormonal conditions
• Treatment of insulin resistance when present
• Evidence-based anti-obesity medications when appropriate
• Ongoing follow-up with a pediatric endocrinologist

Our goal isn't simply to lower the number on the scale. It's to improve long-term health, confidence, and quality of life.

When Should You See a Pediatric Endocrinologist?

A pediatric endocrinologist can help determine whether weight gain is influenced by hormones, genetics, or another underlying medical condition.

You should consider an evaluation if your child has:

• Rapid or unexplained weight gain
• Severe obesity at a young age
• Persistent excessive hunger
• Prediabetes or type 2 diabetes
• Insulin resistance
• High cholesterol
• Fatty liver disease
• PMOS (formerly PCOS)
• Growth or puberty concerns
• A family history of rare endocrine or genetic disorders

Early evaluation often leads to earlier treatment and better long-term outcomes.

Frequently Asked Questions (FAQ)

What is the obesity gene called?

The FTO (fat mass and obesity-associated) gene is the gene most commonly referred to as the obesity gene because it has the strongest association with common obesity.

Is there just one obesity gene?

No. Scientists have identified hundreds of genes that influence body weight. Obesity is usually caused by many genes working together along with environmental and lifestyle factors.

What does the FTO gene do?

The FTO gene helps regulate appetite and feelings of fullness. Some variants are associated with increased hunger and a slightly higher risk of obesity.

Can obesity run in families?

Yes. Families often share both genetics and lifestyle habits. Having relatives with obesity may increase risk, but it does not guarantee that a child will develop obesity.

Should my child be tested for obesity genes?

Most children do not need genetic testing. Testing is generally reserved for children with severe early-onset obesity or features suggesting a rare inherited syndrome.

Does having the obesity gene mean weight loss is impossible?

No. Genetics increase susceptibility, but healthy lifestyle changes, medical care, and individualized treatment remain effective for many children regardless of their genetic background.

The Bottom Line

The FTO gene is the gene most commonly called the "obesity gene," but it is only one part of a much larger picture. Obesity is influenced by many genes working together with nutrition, sleep, physical activity, hormones, medications, and the environment.

Understanding genetics can help families move beyond blame and toward personalized, evidence-based care. If you're concerned that your child's weight may be influenced by hormonal or genetic factors, a pediatric endocrinologist can help identify the underlying causes and develop a treatment plan tailored to your child's unique needs.

About the Author

Natalie Hernandez, MD, is a board-eligible pediatric endocrinologist and Metabolic & Obesity Specialist at LIFE Pediatric Endocrinology. She specializes in childhood obesity, insulin resistance, prediabetes, type 2 diabetes, and PMOS (formerly PCOS), helping families understand the hormonal, genetic, and metabolic factors that influence weight while developing personalized, evidence-based treatment plans.

References

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