Why should we care about obesity? - Economics Observatory

Obesity is increasing in the UK and around the world, including among children from disadvantaged backgrounds. As well as immediate health effects, obesity can have an impact on young people’s learning and future prospects.

Obesity in the UK has been rising dramatically in recent years, particularly for children growing up in deprivation. It is likely to have to negative long-term consequences for their health and for key social and economic outcomes, as well as raising costs to the NHS.

Obesity is usually defined using the ‘body mass index’ (BMI), which is the ratio of an individual’s weight to height (NHS BMI calculator). BMI is a simple summary statistic used by medical professionals as an indicator of whether an individual is overweight and, if so, how overweight they are. Obesity in adults is when BMI is over 30; morbid or severe obesity is when BMI is over 35.

BMI is not a perfect indicator, nor is it the only indicator, that medical professionals care about (see, for example, NHS and Harvard Public Health); excess fat around the waist is another indicator. But BMI is a relatively easy one to measure and track across time and locations.

How many people are obese?

Obesity has risen dramatically in the UK and many other countries, with nearly one in every three adults in England being obese, and around one in 25 being morbidly obese – see Figure 1. The statistics show similar trends in Scotland, Wales and Northern Ireland – and other parts of the world.

Figure 1: Obesity in adults has risen dramatically in England

Source: Public Health England (PHE)

Obesity in children is also high: for example, around one in five 10-11 years in England is obese. Worryingly, children are becoming obese at younger ages and are staying obese into adulthood.

Obesity is more prevalent in more disadvantaged parts of the country, with children living in the most deprived regions of the UK being nearly twice as likely to be obese as those living in the least deprived – see Figure 2. If we focus on those that are severely obese, children in the most deprived regions are over four times as likely to be so as those in the least deprived areas.

Figure 2: Children in deprived areas most likely to be obese

Source: NCMP and Child Obesity Profile, Public Health England

The gap in obesity rates between children growing up in the least and most deprived areas is widening – see Figure 3. In 2006, the gap was 8.5 percentage points; by 2019, it had grown to 13.3. Similarly, looking at severely obese children, the gap between the share of children in the least and most deprived areas grew from 3.1 percentage points in 2006 to 5.3 in 2019. These statistics raise the concern that obesity and associated problems are potentially important drivers of long-term inequalities.

Figure 3: Gap with deprivation is increasing

Source: NCMP and Child Obesity Profile, Public Health England

Why is rising obesity a problem?

The main medical concern about excess weight is excess fat (too much bone or muscle is not a problem). Excess fat is thought to increase an individual's risk factor for a number of diseases including type 2 diabetes, coronary heart disease, strokes and some types of cancer.

In additional to the health risks of obesity to individuals, it also poses the problem of increased healthcare costs. These are a classic example of what economists call ‘externalities’ – costs arising as a result of people’s decisions that affect others who were not involved in the decision-making. In this case, the increased healthcare costs of treating obesity-related illness are paid by all of society, not just those who are obese. The UK government estimates the costs to the NHS to be in the several billions and that they are rising rapidly (PHE, 2017).

We can see evidence of increased healthcare costs if we look, for example, at the number of hospital episodes where obesity is the primary or secondary diagnosis – see Figure 4. This has risen almost fourfold over the past decade. These externalities suggest that policies to reduce obesity could improve social welfare by bringing down these costs.

Figure 4: Obesity-related hospital episodes

Source: NHS Digital

Public Health England (PHE) in England and the Centers for Disease Control and Prevention (CDC) in the United States highlight being obese as a cause of long-term harms in children, due to school absences and behavioural problems at school. As a result, it can have potentially important consequences for children’s long-term social and economic outcomes as well as their health (CDC and PHE).

Good nutrition is essential for both physical and mental growth. A child that is not well nourished will have difficulty concentrating at school. Further, we know that differences in educational attainment are an important driver of the gap in adult earnings between children growing up in disadvantaged versus affluent families (see, for example, Blundell et al, 2020). Thus persistently higher obesity rates in children growing up in deprivation are likely to hurt their future prospects and dampen social mobility – the extent to which young people’s later life outcomes can be independent of their family backgrounds.

Economists have formalised these effects with the label ‘internalities’. These are externalities where the social costs from excess consumption fall on the person themselves in the future rather than someone else.

For children, the long-term consequences of eating an unhealthy diet are not factored into their decision-making – they are likely to be too young to understand the long-term effects. And for some children, their parents do not seem to be accounting fully for these effects either. Obesity and malnutrition are associated with poverty and are likely to be important constraints on the opportunities of children, particularly those growing up in deprivation.

Does it matter what type of calories you eat?

In terms of gaining weight and excess fat, it is primarily calories that matter. It may be that some types of foods (for example, those containing a lot of sugar) lead people to eat more overall, which leads to more weight gain, but ultimately it is the calories that matter.

Nevertheless, excess consumption of some types of foods is also associated, and may even cause, specific diseases. For example, high consumption of salt can harden your arteries, leading to high blood pressure and cardiovascular disease.

Equally, high consumption of foods that have a lot of ‘free sugars’ (sugars added by manufacturers or naturally present in honey and fruit juices) can lead to insulin resistance, which can cause diabetes. Excess sugar consumption has been a particular target of health policies around the world, with the introduction of taxes on sugar-sweetened soft drinks in a number of locations.

Is it only calories that matter: what about exercise?

Weight gain results from eating more calories than you burn in activity. So does increasing activity through exercise lead to weight loss? In principle yes, but the relationship between exercise and weight loss is complicated.

Exercise is good for you for all sorts of other reasons but, on its own, it might not lead to a lot of weight loss. This is partly because you would have to increase the amount of exercise you do by quite a lot, and also because the body responds in complicated ways that might mitigate some of the effects of increasing exercise on weight loss (see, for example, work by Susan Jebb at Oxford, such as this interview and this article: Prentice and Jebb, 2004).

What is the likely impact of Covid-19?

Over the course of the pandemic, food insecurity has risen. The UK already had among the highest rates in Europe (see, for example, work by the Food Foundation tracking food insecurity during the pandemic). Food bank use has also increased, in particular by families with children (see statistics from the Trussell Trust).

It is likely that this situation has led to worse diet quality for children in poorer households. Government policies have partly mitigated these effects through increased support and, after widespread public pressure and backing from footballer Marcus Rashford, free school meals were extended to families during lockdown (see a discussion of this policy by Christine Farquharson).

But the effectiveness of this policy was limited. Data from Understanding Society’s COVID-19 Survey suggest that around half of children eligible for free school meals were not able to access the scheme in April 2020 (Parnham et al, 2020). Children who attended school were also almost six times more likely to get a free school meal than children who did not. And families of children who had a free school meal were more likely to use a food bank than families who could not.

It is too early to tell how the pandemic will affect people’s habits and how much exercise they get. Initial data from Sports England suggest that activity levels were down for some children but up for others (Sports England, 2021). Nevertheless, fewer than half of children and young people met the guidelines proposed by the Chief Medical Officer of doing an average of 60 minutes sport or physical activity a day.

Why has obesity increased over recent years?

There is no easy answer to this question: it is likely to be due to a number of factors. Food has become cheaper over both the very long run and more recently. In the UK, this was particularly the case over the 1980s and 1990s (Griffith et al, 2015).

This could have led people to eat more. Yet increasing the overall price of food seems unlikely to be an effective way to reduce obesity. The reduction in food prices has benefited poorer households, for whom foods represent a significant share of their budget and a much higher proportion than for richer households. In addition, food prices in the UK have risen dramatically in the mid-2000s due to the depreciation of sterling, and are now rising again from increased trade costs due to Brexit.

But changing the relative prices of different foods is a policy that many governments are pursuing – for example, by introducing taxes on sugar-sweetened beverages (see Griffith et al, 2019, for a survey of these policies).

The cost of making and eating nutritious foods is not just the money spent on buying the ingredients, but also the time spent in preparation. Time use has changed considerably over the last few decades, and unhealthy foods can often be much faster to prepare than healthier options (Griffith and Luhrmann, 2016).

Recent work shows that as well as some people eating a healthier diet than others, there is considerable variation in the quality of most individuals’ diets over time. This is likely to be driven by self-control problems in food choice (Cherchye et al, 2019). Work by behavioural economists suggests that people don't always fully pay attention when making decisions (Mullainathan et al, 2008). This may be particularly true for people living in poverty who have a lot of other things to worry about and so experience ‘cognitive overload’ (Mani et al 2013).

What can government do to reduce obesity?

Rising obesity and the problems associated with it suggest that many people are making bad choices over the foods that they buy and eat. We want policies that help people to make better choices in order to reduce the externalities (for example, costs to the NHS) and the internalities (worse future health, social and economic outcomes, such as earnings) of these poor choices.

To design good policy, we need to understand why people are making bad choices and how specific policies – or combinations of policies – affect different people. We also need to understand whether those with the highest externalities or internalities will respond to the policies. And it is important to take account of other effects that the policies might have: are there possible unintended consequences? For example, are firms likely to change their behaviour in response to the policy?

Across a series of articles on the Economics Observatory, we will consider some of the evidence that is feeding into consideration of different policies and how effective they will be. The pieces will consider the potential effectiveness for reducing obesity of taxes to change the relative prices of different foods and of restrictions on advertising of certain foods. In addition, they will address what is happening with ‘food insecurity’ during the pandemic; and how reforms to the benefits system might help to reduce food poverty for children in the UK.

Where can I find out more?

Read about how Henry Dimbleby and his team are developing The National Food Strategy.
Watch Susan Jebb's lecture on Obesity, diet and health research delivered to the Academy of Medical Sciences.
Watch Rachel Griffith's Royal Economic Society Presidential Lecture, Obesity, Poverty and Public Policy.
Watch a short video where Rachel Griffith and Pierre Dubois discuss why people are eating less but putting on weight; or a longer version, which is Rachel's European Economic Association Presidential Address.