Go to the page content
About obesity

Phenotyping obesity: when does excess weight become a disease?

Medical professionals define obesity as a complex and long-lasting disease, influenced by a variety of factors, including genetics, hormones, behaviour, and our surrounding environment.

5 min. read
Woman speaking to doctor

The image is a model

Most will be familiar with the role physical activity levels, diet, alcohol consumption, and other existing medical conditions can play, but at what point does obesity become a disease? And is it plausible for someone with a normal weight to have obesity?

In this article, we look beyond the weighing scale to understand when excess weight becomes a disease.

40-80% of our weight may be determined by genes

What is a phenotype?

Every person is unique, and this uniqueness can be understood and measured by ‘phenotypes’. Unlike its genetic counterpart, 'genotype', a phenotype is a visible trait, such as the colour of your eyes and hair or your height. It even extends to behavioural characteristics like the way you walk or talk. While our genes lay the foundation for these traits, the environment in which we live plays a significant role in shaping them.

Consider identical twins. Genetically, they share the same DNA, yet one may develop obesity while the other does not. This highlights the interplay of genes and the environment.

People living with obesity are not all alike. Our bodies react differently to our environment, leading to different 'obesity phenotypes'. This diversity can be seen across different populations, with certain obesity phenotypes more frequent in specific regions. For example, while abdominal obesity (excess fat focused around the stomach) is prevalent in South Asia, other areas of the world may have different dominant obesity phenotypes. Diversity is also evident between men and women. For example, women are more likely to store peripheral fat around their buttocks, hips, and thighs than men.

Obesity is often associated with metabolic issues, which are problems with the processes in your body that convert the food you eat into energy and other compounds necessary for survival. These issues can include high blood pressure, high blood cholesterol and blood sugar levels, insulin resistance, widespread inflammation, and low levels of “good” fats. However, individuals with obesity may not always have metabolic issues, and individuals with a normal weight may not always have healthy metabolic responses.

How different phenotypes can change the experiences of people living with obesity

Obesity phenotypes can affect how individuals with obesity experience the disease and significantly influence the onset of other diseases or conditions associated with obesity. For example, those living with obesity and unhealthy metabolic responses may be more prone to mental health issues, such as depression, than those living with obesity but have healthy metabolic responses.

Studies have shown that many people with certain mental health conditions are living with overweight or obesity. Specifically

25-60% of those with bipolar disorder,
30-70% with schizophrenia, and
20-50% with depression.

Why phenotypes matter when it comes to obesity management

As we learn more about obesity, the more we understand that it is a distinctly diverse disease. There is no ‘one-size-fits-all’ approach to obesity; by moving away from the simplistic BMI classification of obesity towards a more individualised approach, treatment approaches and weight management programmes can be better tailored to an individual’s phenotype for greater health outcomes.

In a recent study, treatments guided by phenotype resulted in notably higher weight loss after one year. A staggering 79% of those treated based on their phenotype lost more than 10% of their weight compared to only 34% in a non-phenotype guided group.

Obesity research is constantly evolving, and as our understanding develops, so does our ability to address it effectively. This article is just a snapshot of the vast and complex topic of obesity phenotypes to help you understand your weight in more detail. If you want to learn more about obesity phenotypes, please consult your healthcare provider.

  • Lau DCW, Wharton S. Canadian Adult Obesity Clinical Practice Guidelines: The Science of Obesity. Available from: https://obesitycanada.ca/guidelines/science. Accessed August 2023.
  • Shaikh RA, Siahpush M, Singh GK, Tibbits M. Socioeconomic Status, Smoking, Alcohol use, Physical Activity, and Dietary Behavior as Determinants of Obesity and Body Mass Index in the United States: Findings from the National Health Interview Survey. Int J MCH AIDS. 2015;4(1):22-34. doi:10.21106/ijma.53
  • Campbell LV. Genetics of Obesity. Australian Family Physician. 46(7) 2017.
  • Doornweerd, Stieneke et al. “Physical activity and dietary intake in BMI discordant identical twins.” Obesity (Silver Spring, Md.) vol. 24,6 (2016): 1349-55. doi:10.1002/oby.21475
  • Sørensen TI, Echwald SM. Obesity genes. BMJ. 2001;322(7287):630-631. doi:10.1136/bmj.322.7287.630
  • Misra, Anoop et al. “Obesity in South Asia: Phenotype, Morbidities, and Mitigation.” Current obesity reports vol. 8,1 (2019): 43-52. doi:10.1007/s13679-019-0328-0
  • Lumish HS, O'Reilly M, Reilly MP. Sex Differences in Genomic Drivers of Adipose Distribution and Related Cardiometabolic Disorders: Opportunities for Precision Medicine. Arterioscler Thromb Vasc Biol. 2020;40(1):45-60. doi:10.1161/ATVBAHA.119.313154
  • Singla P, Bardoloi A, Parkash AA. Metabolic effects of obesity: A review. World J Diabetes. 2010;1(3):76-88. doi:10.4239/wjd.v1.i3.76
  • Abiri, B., Hosseinpanah, F., Banihashem, S. et al. Mental health and quality of life in different obesity phenotypes: a systematic review. Health Qual Life Outcomes 20, 63 (2022). https://doi.org/10.1186/s12955-022-01974-2
  • Taylor VH, Sockalingam S, Hawa R, Hahn M. Canadian Adult Obesity Clinical Practice Guidelines: The Role of Mental Health in Obesity Management. Available from: https://obesitycanada.ca/guidelines/mentalhealth. Accessed August 2023.
  • Acosta A, Camilleri M, Abu Dayyeh B, et al. Selection of Antiobesity Medications Based on Phenotypes Enhances Weight Loss: A Pragmatic Trial in an Obesity Clinic [published correction appears in Obesity (Silver Spring). 2021 Sep;29(9):1565-1566] [published correction appears in Obesity (Silver Spring). 2022 Jul;30(7):1521]. Obesity (Silver Spring). 2021;29(4):662-671. doi:10.1002/oby.23120
  • Pujia, Roberta et al. “Advances in Phenotyping Obesity and in Its Dietary and Pharmacological Treatment: A Narrative Review.” Frontiers in nutrition vol. 9 804719. 15 Feb. 2022, doi:10.3389/fnut.2022.804719


Was this valuable for you?

You might also like