October 30, 2023
Obesity and Genetics: What is the Connection?
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Is Obesity Genetic?
Identifying the underlying causes of obesity can help equip us to more effectively treat this complex disease. Such insights may also benefit people living with obesity, since understanding the causes can ease some of the stigma and self-blame that sometimes accompany it. “It’s all in your genes” could provide a tidy explanation. It may also open opportunities for personalized medicine. However, genetics is only the start.
A growing body of evidence suggests that obesity is, in fact, genetic. Somewhere between 200 and 500 specific genes have been linked to the disease. Genes can influence things like how a person’s body stores fat, metabolizes nutrients, and signals feelings of fullness. Twin studies have supported the hypothesis that obesity is genetic. Several measures of obesity show a high rate of heritability, including BMI, waist-to-hip ratio, and skinfold thickness.
Whatever the role of genetics, there are typically additional factors at work. A combination of genetic and environmental factors influences body weight.
Genetic Causes of Obesity: Polygenic, Monogenic, and Syndromic Causes
Genetic causes of obesity tend to be polygenic, but can also be monogenic. The latter, owing to mutations in a single gene or groups of genes, are often sydomic and thus relatively rare. Examples include Prader–Willi or fragile X syndrome. Non-syndromic obesity could be monogenic, polygenic, or chromosomal in origin.
Polygenic Obesity: How Multiple Genes Contribute to Weight Gain
Polygenic obesity, as the name suggests, owes to multiple genetic factors. Sixty percent of genetic cases fit this category. According to Hinney and Hebebrand, “obesity results via the interaction of several of such polygenic variants and their combined interaction with environmental factors.”
No one of these gene variants guarantees obesity. Any one of them alone is generally considered low-risk. Many are also found in individuals without obesity. If a gene is found more commonly in individuals with obesity than in those without obesity, it is said to be associated with obesity. Some are found more frequently than others.
The Role of FTO in Obesity
One such gene is the fat mass and obesity-associated gene (FTO), which is found in up to 43% of the population. In the presence of readily accessible food, those with the fat mass and obesity-associated gene may have challenges limiting their caloric intake. The presence of this gene and other genes can cause:
- Increased hunger levels
- Increased caloric intake
- Reduced satiety
- Reduced control over eating
- Increased tendency to be sedentary
- Increased tendency to store body fat
The FTO allele allele associated with obesity is common in people with European ancestry, according to multiple studies and has been identified by genome-wide association studies (GWAS). It acts on a variety of biological and metabolic processes.
Researchers have taken a keen interest in FTO as a potential drug target for treating obesity. Several small molecule drugs and micronutrients have been found to control the expression or activity of FTO, thereby playing a role in regulating metabolism.
Monogenic Obesity: Severe Obesity Caused by a Single Gene
Monogenic obesity is less common, yet potentially easier to identify since it tends to affect people from a young age. Rare, high-risk genetic variations in roughly two dozen genes are known to cause monogenic obesity. The gene mutations linked to monogenic obesity are grouped into three broad categories:
- Those that play a physiologic role in the hypothalamic Leptin-Melanocortin system of energy balance, including leptin, leptin receptor, melanocortin-4 receptor (MC4R), proopiomelanocortin (POMC), and prohormone convertase 1/3 (PC1/3).
- Those necessary for the development of the hypothalamus, including SIM1, BDNF and NTRK2. Mutations of these genes lead to severe obesity.
- Those whose functional relationship to obesity remains unclear, but in which obesity presents as part of a complex syndrome.
Rare single-gene defects cause severe obesity beginning in early childhood and are associated with extremely high levels of hunger. Individuals who developed severe obesity before age two should consider talking to an obesity medicine specialist about being screened for:
- Leptin deficiency
- POMC deficiency
- MC4R deficiency
Syndromic Obesity: The Links Between Genetic Syndromes and Obesity
Syndromic obesity is part of a rare inherited condition, present at birth and often associated with comorbidities. In addition to excess weight patients living with these conditions may also exhibit cognitive delay, dysmorphic features, organ-specific abnormalities, hyperphagia, and other signs of hypothalamic dysfunction.
Some of the more well-known syndromes that include obesity include:
- Prader-Willi syndrome
- Bardei-Bietl syndrome
- Cohen syndrome
An approach to treating or managing one of these syndromes would typically look very different from other types of obesity. Research is underway into molecules acting on the leptin-melanocortin pathway, a potential target in some forms of syndromic obesity.
Emerging Studies: Epigenetics and Obesity
Epigenetics, the study of gene expression that changes during a person’s lifetime due to environmental factors, presents a relatively recent but fertile area of research. Despite the large number of identified genes related to obesity, “these variants do not fully explain the heritability of obesity, other forms of variation, such as epigenetics marks, must be considered,” say Herrera, et. al. in the paper, “Genetics and epigenetics of obesity.” The authors continue, “environmental exposures during critical developmental periods can affect the profile of epigenetic marks and result in obesity.”
These critical developmental periods include pregnancy, with factors like maternal over- or under-nutrition, stress, and exposure to toxins. Early childhood is also a prime time in which poor nutrition is linked with epigenetic effects linked with obesity. Use of antibiotics during this phase is linked with metabolic dysfunction-associated steatotic liver disease (MASLD).
As a person moves through adulthood, environmental factors continue to affect gene expression. Factors linked to adult epigenetic modifications include high intake of sugary beverages, fried foods, and high saturated fats as well as poor sleep and a sedentary lifestyle.
Are Your Genes Your Destiny?
While genetic predispositions to obesity are very real and relevant, they are not the only thing that determines whether a person will develop obesity.
Environmental Factors
Exercise, diet, stress levels can all affect a person’s weight (irrespective of their epigenetic impacts). Even people with a genetic predisposition for obesity can reduce their risk through good nutrition and an active lifestyle. A 2008 study published in the journal Diabetes showed that physical activity offsets the effects of a common variant of FTO. Also consider that genetics would not explain the rapid global rise in obesity.
If someone has genes that predispose them to obesity, they are not predestined to develop obesity. While these genes can increase appetite and reduce metabolism, following a consistent treatment plan that incorporates effective nutritional, physical activity, and behavioral approaches can help prevent and treat obesity.
A patient struggling with weight may benefit from seeing an obesity medicine specialist to help develop a comprehensive medical obesity treatment plan.
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Andreasen CH, Stender-Petersen KL, Mogensen MS, Torekov SS, Wegner L, Andersen G, Nielsen AL, Albrechtsen A, Borch-Johnsen K, Rasmussen SS, Clausen JO, Sandbaek A, Lauritzen T, Hansen L, Jørgensen T, Pedersen O, Hansen T. Low physical activity accentuates the effect of the FTO rs9939609 polymorphism on body fat accumulation. Diabetes. 2008 Jan;57(1):95-101. doi: 10.2337/db07-0910. Epub 2007 Oct 17. PMID: 17942823.
Duis, J., Butler, M. G., Syndromic and Nonsyndromic Obesity: Underlying Genetic Causes in Humans. Adv. Biology 2022, 6, 2101154. https://doi.org/10.1002/adbi.202101154
Genes Are Not Destiny, Harvard T.H. Chan School of Public Health, https://www.hsph.harvard.edu/obesity-prevention-source/obesity-causes/genes-and-obesity/
Herrera BM, Keildson S, Lindgren CM. Genetics and epigenetics of obesity. Maturitas. 2011 May;69(1):41-9. doi: 10.1016/j.maturitas.2011.02.018. Epub 2011 Apr 3. PMID: 21466928; PMCID: PMC3213306.
Hinney A, Hebebrand J. Polygenic obesity in humans. Obes Facts. 2008;1(1):35-42. doi: 10.1159/000113935. Epub 2008 Feb 8. PMID: 20054160; PMCID: PMC6444787.
Hélène Huvenne, Béatrice Dubern, Karine Clément, Christine Poitou; Rare Genetic Forms of Obesity: Clinical Approach and Current Treatments in 2016. Obes Facts 30 June 2016; 9 (3): 158–173. https://doi.org/10.1159/000445061
Ruth J.F. Loos, A. Cecile J.W. Janssens, Predicting Polygenic Obesity Using Genetic Information, Cell Metabolism, Volume 25, Issue 3, 2017, Pages 535-543, ISSN 1550-4131, https://doi.org/10.1016/j.cmet....
Ekta Tirthani; Mina S. Said; Anis Rehman. Genetics and Obesity. Treasure Island (FL): StatPearls Publishing; 2023 Jan.

Not All Obesity is the Same: Rare Genetic Forms of Obesity
1 On the other hand, there are other rare types of obesities resulting from some rare but highly impactful genetic variants or deletions (i.e. Bardet- Biedl Syndrome, POMC deficiency, LEPR deficiency, Prader-Willi Syndrome), or even acquired hypothalamic damage (i.e. acquired hypothalamic obesity) ( Figure 1). Rare genetic variants or damage to the hypothalamus can lead to impairment of a critical pathway, the hypothalamic melanocortin-4 receptor (MC4R) pathway, otherwise known as the leptin-melanocortin pathway. This pathway is responsible for regulating hunger and energy expenditure and any impairment in the pathway leads to rare MC4R pathway diseases. 2-3 It is important to be aware of this unique subset of obesity associated with MC4R pathway diseases as MC4R pathway diseases are likely underdiagnosed and early identification of MC4R pathway diseases is essential for optimal disease management. 4-6 Figure 1: Rare Hypothalamic MC4R Pathway Diseases The MC4R signaling pathway regulates hunger, satiety, and energy expenditure, consequently affecting body weight. 7-8 Genetic variants that impair function of genes involved in the MC4R Pathway function, or physical damage to the hypothalamus leads to decreased alpha-MSH and impaired downstream activation of the MC4R pathway. 9 Figure 2: Impairment of the MC4R Signaling Pathway MC4R pathway diseases caused by rare genetic variants are classified as monogenic or syndromic in nature. 10 Monogenic obesity refers to obesity due to variants in single genes (e.g. POMC deficiency, LEPR deficiency, PCSK1 deficiency, SRC1 deficiency, SH2B1 deficiency, etc.) along the MC4R pathway. Syndromic obesity refers to obesity that is also due to genetic variants or deletions in the pathway but also associated with additional phenotypes such as organ-specific developmental abnormalities, such as visual impairment, renal anomalies, cognitive impairment, dysmorphic features, etc. 10-11 Rare Genetic Diseases of Obesity Provider Listing A patient's diagnostic journey can be complex and may take years.

The Importance of Nutrition Quality in the Treatment of Obesity
Comprehensive obesity management ideally should utilize a spectrum of treatments -- nutrition therapy, physical activity, behavior modifications and medical interventions such as medication management. Medical nutrition therapy is an essential pillar regarding treatment of patients with obesity. Nutrition quality is just as critical as calorie reduction in obesity treatment. By reducing hunger signals, patients may find it easier to adhere to their nutritional goals. The Mediterranean diet, Dietary Approaches to Stop Hypertension (DASH), and plant-forward diets each offer distinct benefits and varying levels of evidence supporting their role in obesity care. Source https://pubmed.ncbi.nlm.nih.gov/32059053/ The Mediterranean diet has the most consistent evidence for weight management and cardiometabolic benefits. The effect of the DASH diet with supervised physical activity decreases body weight, waist circumference, and fat mass. (Source: https://pubmed.ncbi.nlm.nih.go... ) When guiding patients on dietary choices, it is essential to consider cost and accessibility. For clinicians seeking additional guidance, the 2024 OMA Obesity Algorithm—Important Principles for the Effective Treatment of Patients with Obesity is a valuable resource and is free for OMA members.

The Obesity-CVD Connection: Understanding Risks and Treatment Strategies
Obesity is a major risk factor for cardiovascular disease (CVD), contributing to hypertension, dyslipidemia, and metabolic dysfunction. Effective Treatment Strategies for Reducing Cardiovascular Risk A comprehensive approach to obesity treatment can significantly lower cardiovascular risk. Pharmacotherapy plays a critical role in obesity management, particularly for patients at high cardiovascular risk. SGLT2 inhibitors, originally developed for diabetes management, have also shown promise in obesity treatment and cardiovascular protection. These medications offer an innovative approach to obesity and cardiovascular disease management, providing an alternative to or adjunct to traditional lipid-lowering and antihypertensive therapies. The Obesity Medicine Association (OMA) provides a comprehensive Obesity Algorithm® , which outlines individualized treatment strategies, including pharmacologic options tailored to patients with cardiovascular comorbidities. These guidelines reinforce the necessity of an individualized, multidisciplinary approach to obesity management in patients with existing heart disease. Obesity and cardiovascular disease are intricately linked, making obesity management a crucial component of cardiovascular risk reduction. OMA Resources for Clinicians For clinicians seeking to enhance their expertise in obesity and cardiovascular disease management, the Obesity Medicine Association (OMA) offers a variety of resources.