Having obesity isn’t due to genetic factors alone

By Heather Jones 

 Medically reviewed by Karina Tolentino, RD

Genetics can play a role in having obesity. Twin studies have found the heritability of obesity to be approximately 40% to 75%. Up to 500 obesity-related genes have been recognized in humans.¹

Mahmoud R, Kimonis V, Butler MG. Genetics of obesity in humans: a clinical review. IJMS. 2022;23(19):11005. doi:10.3390/ijms231911005

Although evidence for a genetic link with obesity is strong, the contribution of genes to obesity is considered small. Environmental factors such as diet and physical activity are believed to be a bigger influence on obesity than genetics alone.²

This article will discuss the link between genes and obesity, genes and inheritance, known risk factors, comorbidities, and obesity, and what to focus on.

Alessandro Biascioli / Getty Images

Genes and Obesity: A Genetic Link?

Research shows obesity results from an interaction between environmental and innate biological factors.³

The specific genetic influences of obesity are still being studied, but up to 500 specific genes have been linked to obesity. These genes can affect factors such as:⁴

• How the body stores fat

• The metabolism of nutrients

• Signals for feelings of fullness

• Tendency to be more sedentary

• Hunger levels

• Food cravings⁵

• The tendency to eat as a stress-coping mechanism

There also appears to be a high rate of heritability with some measures of obesity, such as:⁴

• Body mass index (BMI)

• Waist-to-hip ratio

• Skinfold thickness

Genes alone do not determine obesity, as evidenced by the rate obesity levels have risen in recent decades. This increase has happened too quickly to be explained solely by genetics.⁶

Most instances of obesity are considered polygenic obesity, meaning multiple genetic factors are playing a role rather than any single gene alone.⁴

Genetics isn't considered to cause obesity; rather, they can make some people more predisposed to it. This means that the genes passed down to them can make some people more likely to gain weight (or have difficulty losing it) than others because of their influence on and interaction with environmental factors, like eating and physical activity patterns.⁵

Does Everyone With Obesity Have a Genetic Link?

Not everyone with a genetic predisposition to obesity will have obesity and not everyone with a strong genetic predisposition to it.⁵

Genes are more likely a strong contributor to your obesity or overweight if most or all of the following apply to you:

• You have been overweight or had obesity most of your life.

• You have at least one parent, or several other blood relatives who are significantly overweight.

• You have difficulty losing weight even with several months of physical activity and a low-calorie eating plan.

People with a strong genetic predisposition to obesity often find it difficult to lose weight or maintain weight loss with what some consider sheer willpower. They often require help from a healthcare provider and may need treatments such as medications or weight loss surgery.

Genetic factors may play less of a role with your obesity or overweight if most or all of the following apply:

• The availability of food strongly influences you

• You are moderately overweight, but can lose weight when you follow a reasonable diet and exercise plan

• After losing weight, you tend to regain it during the holiday season, at times, you experience psychological or social problems, or after you change your eating or exercise habits

Several studies have shown that adopting practices such as being physically active can offset genetic predisposition.

One study found that physically active participants had the same BMIs whether they had a genetic predisposition to obesity or not. Other research has found that those with one of the main gene variants associated with obesity had a higher risk of obesity than those who did not, but that those who carried the gene variant and were active had a 30% lower risk of obesity than those who carried the gene variant and were not active.²

Thrifty Genes

About 85% of people carry so-called thrifty genes. These genes were of great benefit to our ancestors as they helped people conserve energy and store body fat to live off during times when food was scarce. The people with these genes were more likely to survive than those without, meaning these genes became favored genes, making people with them better able to survive and reproduced.⁵

Now, food is readily available, people don't have to expend energy to hunt or harvest it, and those thrifty genes are no longer needed. Unfortunately, genetic evolution moves much slower than our environmental adaptation, so these genes and their instructions to store fat persist even when unnecessary.⁶

Epigenetics

A person's genes are determined at the time of conception, and are set for life, but the activity of the genes is not. How genes are expressed (the process by which a gene's encoded information is turned into a function) can be influenced by environmental signals, including genes that affect weight regulation.⁷

This "programming" happens in the womb. For example, if a pregnant person experiences food shortages, their baby is more likely to be small, but if food is available after birth, the baby can put on large amounts of fat and be more likely to experience obesity.

Inherited Obesity

Most of the time, many genes interact with environmental factors to influence obesity, but rarely a clear pattern of inherited obesity can be found. This is called monogenic obesity and is caused by a variant of a single gene.⁸

High-risk genetic variations in approximately 24 dozen genes are known to cause monogenic obesity.⁴

Monogenic obesity has the following characteristics:

• It is rare.³

• It is typically early-onset and severe.

• It involves either small or large chromosomal deletions or single-gene defects.

• It is inherited in a Mendelian pattern, meaning a single gene (two alleles) inheritance pattern, with dominant and recessive traits.

• It may result from spontaneous mutations in single genes.²

• It involves mutations in genes that play essential roles in appetite control, food intake, and energy homeostasis, primarily in genes that code for the hormone leptin, the leptin receptor, pro-opiomelanocortin (POMC), and the melanocortin-4 receptor (MC4R).

A person who develops severe obesity before the age of 2 years should be considered for screening to look for:⁴

• Leptin deficiency

• POMC deficiency

• MC4R deficiency

Syndromic Obesity

Syndromic obesity is a rare form of obesity that is part of multiple clinical characteristics such as cognitive delay, organ-specific abnormalities, and dysmorphic features.⁹

Some examples of syndromic obesity due to chromosomal defects include:

• Prader-Willi syndrome¹

• Down syndrome

• Bardet–Biedl syndrome

• Fragile X syndrome

• Alstrom syndrome

• Cornelia de Lange syndrome

• Albright’s hereditary osteodystrophy⁹

• WAGR syndrome

Known Risk Factors Linked to Obesity

In addition to genetics, there are many factors that affect weight regulation, and can be associated with obesity. Many of these influences are believed to be significant contributors to the recent rise in rates of obesity.

Some of these factors include:

• Social determinants of health: These are conditions (in which people live, work, learn, and play) that support (or do not support) health, such as affordability and accessibility of nutritious food options, peer and social supports, marketing and promotion, community design and the policies that determine them; also includes food, drink, and physical activity offered by childhood centers, schools, or communities, which affects eating and activity patterns.⁸

• Illnesses: Some illnesses may cause weight gain, such as Cushing's disease.

• Medications: Certain medications may lead to weight gain, such as steroids and some antidepressants

• Increased food/calorie intake: Weight gain is influenced by factors such as the recent availability of food at all hours and an influx of highly processed foods, fast foods, and high-sugar beverages (along with marketing campaigns promoting them).²

• Decreased physical activity: This is influenced by an increase in sedentary activities, such as screen time. A decrease in physical activity in children has especially been noted.

• In-utero exposures: This is also called fetal programming. Parental smoking during pregnancy and gestational diabetes can both increase the risk of the babies having overweight in the future.⁵

• Infant feeding: Babies who were breastfed for more than three months are less like than those who were not breastfed for more than three months to have obesity as adolescents.

• Obesogenic environment: The way many people live encourages more eating and less exercising, as well as affecting sleep and stress levels. Also influenced by factors such as increasing availability of food, increasing portion sizes, and less opportunities for physical movement.

• Lack of sleep: Lack of sufficient sleep can disrupt the hormones that control hunger and appetite.

• Stress: Stress can affect diet and appetite, leading to an increase in food intake and in eating less-nutritious comfort food.

• Childhood habits: Regularly eating less nutritious foods (such as highly processed foods or sugary drinks), and/or engaging in sedentary activities instead of physically active activities can set patterns that persist into adulthood. Encouraging or forcing children to eat more when they indicate they are finished can also disrupt their ability to listen to signals of hunger and fullness.¹⁰

• Learned behaviors about food: These include using food as a reward, for comfort, or as an expression of love.

What Is and Is Not Controllable With Developing Obesity?

We cannot control having a genetic disposition to obesity. Nor can we control our past. We also can't control every aspect of our environment that influences weight regulation.

Many adults with obesity have years-long eating, exercise, sleep, stress, and other patterns that have contributed to weight gain, and those can be hard to change.

People can gain control over their lifestyle habits. Developing and sticking to healthy lifestyle practices, such as eating various nutritious foods and getting plenty of exercise, can be difficult, but it is within our control.

If you want to make these changes but are having difficulty or don't know where to start, talk to your healthcare provider or contract a registered dietitian for guidance.

Comorbidities and Obesity

Not everyone with obesity develops significant health problems, but having obesity can increase the risk of health concerns such as:

• High blood pressure (hypertension)¹¹

• High cholesterol

• Coronary heart disease

• Type 2 diabetes

• Stroke

• Breathing problems, such as asthma

• Sleep apnea

• Joint problems, such as osteoarthritis

• Musculoskeletal pain or discomfort

• Certain cancers, such as breast and bowel

• Gallstones and gallbladder disease

• Psychological problems, such as depression and anxiety

• Low self-esteem

• Lower self-reported quality of life

• Premature death

• Social problems (in children)

• Atherosclerosis (fatty deposits that narrow the arteries)¹²

• Gastroesophageal reflux disease (GERD)

• Reduced fertility

• Liver disease

• Kidney disease

• Pregnancy complications, such as gestational diabetes and preeclampsia

What to Focus on Now

Treatment for obesity does not focus largely on genetics. Strategies for obesity treatment primarily target environmental, social, and behavioral factors, such as:¹³

• Eating well: Emphasize a variety of fruits and vegetables, whole grains, lean proteins, and low-fat dairy products. Limit foods and beverages with added sugars, saturated or trans fats, or sodium. See the Dietary Guidelines for Americans and the Centers for Disease Control and Prevention's (CDC) Healthy Eating for a Healthy Weight for more information.⁸

• Getting active: As a general guideline, children aged 3 years to 5 years should be physically active throughout the day, children aged 6 years to 17 years need at least one hour of moderate to vigorous physical activity every day, and adults need 150 minutes of moderate intensity physical activity per week. See the Physical Activity Guidelines for Americans for more information.

• Sleeping well: Teenagers need eight to 10 hours of sleep each night, and adults need seven or more hours. Make sure you are getting quality sleep as well as enough sleep. Consider having a sleep assessment done, especially if you have signs of sleep apnea (such as snoring)

Sometimes, lifestyle changes may not be enough to lose weight and keep it off long-term effectively. For severe obesity, bariatric surgery with long-term follow-up is the most successful treatment. If you think this surgery may benefit you, talk to your healthcare provider.⁹

Summary

Obesity has genetic links, but in most cases, individual genes associated with obesity play minor roles in the development of obesity.

Genetics can predispose people to developing obesity. This means they are more likely to gain weight and have more difficulty losing it, but it does not necessarily mean they will develop overweight or obesity.

Obesity is usually the result of an interaction between several factors, including genetics, environment, and behaviors.

Obesity is associated with several comorbidities, including heart disease, type 2 diabetes, and sleep apnea.

Treatment for obesity focuses on lifestyle and behavior changes, such as healthful eating, physical activity, and good quality sleep. Severe obesity may be most effectively addressed with bariatric surgery.