Despite the scientific evidence that demonstrates otherwise, obesity is commonly misconceived as being a result of poor choices made by individuals. In this opening article of Economist Impact’s Science of Obesity series, we explore the various and interconnected web of factors that influence obesity and discuss why they matter.

In 2020, nearly 1 billion people around the world were living with obesity.¹ There are no signs that rates are stabilising in any country, let alone falling. The World Obesity Federation estimates that by 2035 this figure will continue to rise, with half of the world’s population living with overweight or having obesity (Figure 3).¹

Most worrying is the number of children and adolescents with obesity, as this is likely to continue into adulthood. Whereas in 1975 less than 1% of all children aged 5-19 were affected by obesity, that figure is now 8-10% and is predicted to rise to 18-20% by 2035.^{1, 2} Obesity levels rose more quickly than predicted during the covid-19 pandemic, especially in children under five years old.³

The WHO has classified obesity as a chronic disease.⁴ It is now considered to be an epidemic with multiple, complex causes including inequalities and social determinants of health, and is not simply due to an individual’s lack of willpower.⁴

The burden of obesity for an individual is immense. Overweight and obesity account for more than 1.3m deaths globally each year and are linked to more deaths worldwide than underweight.^{6, 7} Obesity is directly linked to at least 38 noncommunicable diseases (NCDs) including diabetes, hypertension, cardiovascular disease, chronic kidney disease, metabolic dysfunction associated fatty liver disease, osteoarthritis, depression and 13 types of cancer.⁸ These conditions are often interlinked, increasing the risk of simple multimorbidity (two conditions) and complex multimorbidity (four or more conditions), with higher risks for people with more severe obesity.⁸ Indeed, after increasing age, obesity is the second predictor of covid-19 complications or mortality.⁹ Having multiple conditions reduces individuals’ quality of life and puts a strain on healthcare resources. 

Childhood obesity is linked to lower self-esteem, poorer school performance, bullying and poorer health, including metabolic disorders such as type 2 diabetes.¹⁰ In 2021 around 41,600 new cases of type 2 diabetes were diagnosed in children and adolescents worldwide.¹¹ This is particularly alarming because type 2 diabetes is preventable and leads to earlier complications when it develops in childhood.¹² 

The World Obesity Federation predicts that the continuing rise in overweight and obesity is likely to cost at least US$4.3trn by 2035 in terms of global direct healthcare costs (treatment costs for obesity and associated diseases) and indirectly through lost employment, early retirement and premature death.¹ There are clear individual, social and economic cases for investing in obesity prevention and management today to reduce these future costs.

The traditional view that obesity is due to lack of individual responsibility needs to be dispelled, as it does not take into account the many physiological, biological, genetic, social, cultural and environmental factors that may affect someone’s risk of developing obesity. This inaccurate and simplistic view is also stigmatising, leading to discrimination.^{13, 14} 

For instance, globally our environment is becoming increasingly obesogenic—in other words, more and more it facilitates obesity.¹⁵ Advertising and marketing have influenced social and cultural norms around food and drink in many societies, including by normalising fast-food consumption and promoting the consumption of unhealthy foods. Technological and digital advances have led to more sedentary jobs and pastimes. We explore the role of these broader social determinants of health in impacting obesity in a separate article in the Science of Obesity series. 

Interventions that are aimed at supporting individuals to change their diet and increase physical activity tend to follow a pattern of weight loss, plateau then progressive weight regain.^{15, 16} One reason for this is that hormonal changes that influence appetite regulation occur in the body as a defence mechanism, making further weight loss more difficult.^{15, 16} We explore the role that biology plays in influencing obesity outcomes in another article within this series. Encouraging people living with obesity to focus on making sustainable, positive changes to their diet quality and physical activity whilst seeking guidance and support from healthcare professionals can be more beneficial and motivating than focusing solely on weight loss as an indicator of “success” or “failure”.^{13, 15} Also, as one study puts it, “long-term benefits require long-term attention”, so people living with obesity who are making such lifestyle changes require sustained support.¹⁵ All people living with obesity also require access to obesity prevention and management services.¹⁹ 

A common misconception is that reducing one’s caloric intake and becoming more active is a “one size fits all” solution for treating obesity. However, the reality of the matter is that there is substantial evidence showing that obesity is influenced by various drivers that lie outside of an individual’s control. For instance, on a biological level, the body’s innate physiological response can play a significant role in defending against weight loss. On a broader societal level, environmental factors such as a lack of access to affordable healthy food options or limited opportunity to safely and affordably engage in physical activities can influence obesity outcomes.¹⁷ Policy interventions must recognise the role of factors outside of an individual’s control if they are to effectively address obesity rates.

The WHO officially recognised obesity as a global epidemic in 1997.¹⁸ Efforts since then could be described as well-intended but inadequate at a national and global level. No country is on track to meet the two Sustainable Development Goals most relevant to obesity—reducing premature mortality from NCDs by a third and ending malnutrition (wasting and overweight) in children under 5 by 2030.⁴ Without tackling obesity, these targets will not be met.⁴ One explanation for why these efforts may not have worked so far is because they fail to address the key societal and cultural factors that determine food choices and activity levels, says Arya Sharma, professor of medicine at the University of Alberta, Canada. 

The WHO Acceleration Plan to Stop Obesity focuses on supporting 28 countries across the six WHO regions to adopt a range of evidence-based, multi-sectoral strategies.⁴ The idea is to share learnings, refine interventions and roll them out to other, comparable countries. However, only a handful of the proposed policy interventions have been prioritised by these countries in their obesity plans so far (Figure 2).