Genetics And Obesity: Any links? Is Obesity Your Destiny?

Obesity is an energy imbalance in a person consuming more calories than his body requirement. Why is it a serious health issue? It causes deadly diseases like stroke, heart disease, diabetes, and cancer worldwide. The rapidly rising population affected by obesity creates an “obesogenic” environment. According to which people get an excessive amount of food and less opportunity for physical activity. Not all people are affected by obesity in an “obesogenic” environment. Can there be any link between genetics and obesity? If yes, then, what percentage is it? Let’s continue our journey in finding the answers.

The World Health Organization is defining obesity as an epidemic, and the rate is increasing worldwide. Whereas CDC realized that  42.2% of Americans older than 19 years had obesity from 2017 to 2018. The Organization for Economic Co-operation and Development (OECD) estimated that 3 out of 4 Americans would be obese by 2020. And 1 out of 4 Americans will be severely obese by 2030.

What is obesity?

Obesity means having excess body fat compared to your height and weight. And, it is calculated by a system known as body mass index (BMI), a simple calculation for adults that gives a value depending on age and sex. For adults, the Center for Disease Control and Prevention (CDC) defined obesity as having a BMI of 30.0 or more.

In the BMI system, obesity for adults above 19 years old can be classified as below:

18.5 or Below: Underweight

18.5 to < 25.0   :  Normal

25.0 to <30.0    :  Overweight

30.0 to <35.0    :  Class 1 obesity

35.0 to <40.0    :  Class 2 obesity

40.0 or Above:  Class 3 obesity

Is obesity genetic or environmental?

Many reasons cause obesity. Debates and variations in the scientific literature are continued. And, an average figure from scientific research studies estimates 40% of genetic and 60% environmental factors are responsible for obesity.

The environmental factors of obesity usually refer to less physical activity opportunities, a high amount of food consumption, indoor entertainment media, high sweetened beverages, etc. In social globalization, we are developing a habit of consuming excessive amounts of food. For instance, snacking while watching Netflix. As a result, our physical activity is reducing, resulting in an imbalance of calorie gain and burn. 

Research done by different scientists has concluded that external environmental factors are not the only reason people gain weight. These factors include eating an unhealthy diet and an inactive lifestyle. But, genetics also plays a crucial role on obesity.

Habits such as excessive alcohol drinking and smoking can affect the genetic cause of obesity. So does consuming huge amounts of unhealthy food and having a sedentary lifestyle.

Considering obesity could have a genetic component is not surprising because it often runs in families. Several studies showed that BMI is positively related to parental obesity. Children from obese parents have a higher risk of being obese compared to children from non-obese parents. 

How Can Genes and Obesity be Linked?

Genes determine the way our body responds to different changes in their environment. There have been many studies in recent decades, suggesting that a sizable portion of the weight variation among adults results from genetic factors. Further studies have compared obese and non-obese people to find variations in genes that could influence:

– the tendency to over-eat or be sedentary,

– an increased tendency to store body fat.

These studies found some genes that may increase one’s hunger and tendency to store body fat. There are two kinds of genetic obesity. They are:

Monogenic Obesity

Rarely, a single gene causes a clear pattern of inherited obesity in a family, known as monogenic obesity.

Polygenic Obesity

A complex interaction of multiple genes causes most obesity. It is known as polygenic obesity.

One explanation of the obesity epidemic is the “Thrifty genotype” hypothesis. It says the genes that helped our ancestors survive famines are now affected by environments where there is plenty of food all year.

Single Gene or Monogenic Obesity

These are rare forms of obesity resulting from a continuous mutation in single genes. Researchers have noticed these mutations in genes that play a crucial role in food intake and digestion, and energy homeostasis. MC4R is the most common gene that causes it. By now, researchers identified nine genes as the cause of single-gene (monogenic) obesity. However, researchers found changes in MC4R in a tiny portion of obese people (<5%). People who are affected by this gene feel extreme hunger and become obese by consistently overeating.

Genetic syndromes such as Prader-Willi and Bardet-Biedl syndromes can also cause obesity.

Multiple genes or Polygenic Obesity

Evidence from human linkage studies, association studies, animal models, and twin studies suggests that obesity has a genetic component. Not only a single gene is responsible; it’s believed that it results from multiple multifunctional genes. Based on data from more than 25,000 twin pairs, the estimates for BMI are 0.74 for “identical twins,” 0.32 for fraternal twins, 0.25 for siblings, respectively. This study suggests a strong genetic influence on a person’s BMI.

Effects of these Genes and Obesity

The genome-wide association has found that more than fifty genes associated with obesity can initiate a minor effect. Most of the time, obesity results from the complex interaction in many genes and environmental factors.

The effects of these genes can produce includes:

Boosts one’s hunger level.

Increase one’s calorie intake.

Influence one’s body to store excess fat.

Reduce one’s satiety.

Decrease one’s control over eating habits.

Increase one’s tendency to be sedentary.

Effects of family history in obesity

Nowadays, obesity is a significant public health issue worldwide. There are many contributing factors to obesity; one of them is family history. A family history of obesity, hypertension, diabetes, or stroke is a significant risk factor for obesity. A family history of hypertension has a higher diastolic BP and BMI. Those with a family history of obesity have a higher BMI, higher concentrations of glucose, triglycerides, uric acid, cholesterol, and increased diabetes; with an increase of age, more pathological expressions can develop in this high-risk group. Health professionals should utilize every opportunity to a family member in health education.

Genes Control Energy Balance 

The brain regulates food intake by receiving signals from fat cells called Adipose tissue the digestive tract, and the pancreas. Hormones such as insulin, ghrelin, leptin, and other small molecules transmit these signals. Our brain processes these signals and responds with instruction to the body: either eat more, reduce energy usage, or do the opposite. In distinction, if energy utilization is less than energy expenditure, a state of negative energy balance results characterized by the mobilization of energy from adipose tissue.

Genes control these input and response signals, preventing food intake. Hence, a small change in these genes can cause them to work unpredictably. 

Now let’s discuss some association of Genes and Obesity and their role in balancing energy:

Gene Symbol: LEP

Gene Name: Leptin

Role in energy balance: Leptin plays an essential role in regulating energy homeostasis, immune functions, glucose, and lipid metabolism.

Gene Symbol: ADIPOQ

Gene Name   : C1q-,Adipocyte-,and collagen domain-containing.

Role in energy balance: Produced by fat cells, adiponectin promotes energy expenditure.

Gene Symbol: FTO

Gene Name: Fat mass- and obesity-associated gene.

Role in energy balance: Promotes food intake.

Gene Symbol: LEPR

Gene Name: Leptin receptor

Role in energy balance: By consuming leptin, inhibits appetite.

Gene Symbol: PCSK1

Gene Name: Proprotein convertase subtilisin.

 Role in energy balance: Regulates insulin biosynthesis.

Gene Symbol: PPARG

Gene Name: Peroxisome proliferator-activated receptor-gamma.

Role in energy balance: Stimulates lipid uptake and development of fat tissue.

Gene Symbol: INSIG2

Gene Name: Insulin-induced gene 2

Role in energy balance: Regulation of cholesterol and fatty acid synthesis

Gene Symbol: MC4R

Gene Name: Melanocortin 4 receptor

Role in energy balance: By binding to the alpha-melanocyte-stimulating hormone, stimulates appetite.

We can see that these genes play a crucial role in balancing energy in our bodies. But, genes can’t always be blamed. You become obese by inheriting faulty genes from ancestors; sometimes, the genes get damaged by the environmental factors causing obesity.

Your Genes Are Not Your Destiny

A common misconception among us is that if their genes are faulty, they are predestined to be obese. Don’t worry, that’s not true. In 2008, Dr. Andreasen and colleagues demonstrated a study with over 17000 Danes.

Another study stated that people with an obesity-promoting gene and inactivity had a higher BMI than people with obesogenic genes and obesity with an active lifestyle.

Genes can reduce metabolism and increase hunger; a consistent treatment plan that includes physical activity and a healthy diet can help prevent and treat obesity. If we understand genetic contributions to obesity and gene-environment effects better, it will be easy for us to yield promising obesity prevention and treatment strategies.