Genetic Obesity: Are Genes the Cause of Obesity?

How Genes Affect Body Weight – What Is Genetic Obesity?

The probability of a child becoming obese increases significantly if their parents are obese:

• 80% if both parents are obese,

• 40% if only one parent is obese.

However, this is not usually due to genetics alone. The primary cause is the inheritance of dietary patterns and lifestyle habits.

Many researchers have searched for the so-called “obesity gene,” but it has yet to be found. Mutations in individual genes—or even groups of genes—can influence body weight. They may lead to metabolic disorders, impaired nutrient absorption, or disrupted appetite regulation.

Genetic factors contributing to obesity certainly exist. However, they should not be considered in isolation from environmental factors, which play the most significant role in obesity development.

Monogenic Obesity

Monogenic obesity refers to a group of rare conditions caused by mutations in genes that regulate appetite.

Hyperphagia
This includes, for example, mutations in the leptin gene (LEP – a hormone produced in fat tissue, responsible for satiety) and its receptor.
People with this defect often exhibit hyperphagia, meaning constant food-seeking behavior and aggression when denied food. It’s important to note that even here, obesity results primarily from uncontrolled and excessive food intake.

MC4R Gene Mutation
Another defect is a mutation in the melanocortin 4 receptor gene (MC4R), the most common monogenic mutation. It accounts for about 4% of all cases of severe obesity (BMI >35–40).
In addition to increased body weight due to impaired satiety regulation, affected individuals may also exhibit higher muscle mass and increased bone mineral density.

More rarely, monogenic obesity is caused by a mutation in the proopiomelanocortin receptor gene (POMC).

Genetic Obesity as Part of a Syndrome

Obesity may also be one component of rare genetic syndromes such as Prader-Willi, Bardet-Biedl, or Alström syndrome.
The causes are not fully understood and often involve damage to more than one gene.

In these syndromes, pathological obesity is caused by factors such as hyperphagia and a reduction of basal metabolic rate (BMR) by approximately 15%.
These conditions are often accompanied by other developmental anomalies, such as intellectual disabilities or organ dysfunction. Excess weight in these cases can lead to severe complications, including cardiovascular disease and type 2 diabetes.

Polygenic Obesity

The most common form of obesity is polygenic obesity, resulting from gene–environment interactions.

It does not involve specific mutations or chromosomal abnormalities, but rather polymorphisms—genetic variations that alter protein function.
Genetic predisposition can contribute to the development of obesity, but the main factors remain diet quality and physical activity.

Changes in the DNA code, when combined with an unfavorable environment, may lead to excessive fat accumulation. The role of gene polymorphisms in obesity is still under investigation.

The FTO Gene and Obesity Risk

The best-studied polymorphism is a variation in the FTO gene. Depending on one’s genotype, there may be a stronger tendency toward obesity. However, this is strongly correlated with lack of physical activity.

An effective approach to weight loss in people with this predisposition involves regular physical activity and fat intake control.

Genetic Testing and Obesity

More and more diet clinics offer genetic testing to personalize dietary recommendations.

Being aware of specific genetic polymorphisms that increase the risk of metabolic disorders can be helpful during weight-loss efforts.
However, it’s important to remember that such tests do not cover all relevant genes, and focusing on a selective group may be misleading.

When to Search for the Cause of Obesity in Your Genes

Genetic predisposition can sometimes increase the likelihood of overweight or obesity.
However, this usually happens only when combined with poor diet and physical inactivity.

The most effective way to prevent obesity is still a healthy, balanced diet combined with regular exercise.

What If Your Weight-Loss Diet Doesn’t Work?

1. First, assess whether your diet creates a modest caloric deficit based on your actual needs. Also, consider snacking and beverages consumed throughout the day.

2. Second, review your physical activity level.

If you’re sure you’re doing everything correctly, run basic blood tests. Consult your doctor to decide which markers to check first.

If results come back normal, you might consider exploring genetic causes.
Still, remember that the mutations discussed above are very rare. Genetic testing may offer insight, but never abandon the fundamentals of a healthy lifestyle.
Even with a genetic predisposition, a balanced diet and regular exercise are the foundation of maintaining a healthy body weight.