"Four million people died in 2015 as a result of being too tubby, struck by cancer, heart disease, diabetes and other killer conditions," reports The Sun.

This is based on a global study that looked at how the proportion of people who are overweight and obese has changed over time. This was determined by recording body mass index (BMI), where a BMI of 25-29.9 means being overweight and 30 or above is being obese.

Researchers then assessed the link between having an unhealthy BMI and health outcomes including cardiovascular disease, diabetes and cancer.

It found that, despite public health efforts, obesity is on the rise in almost every country and in both adults and children. Prevalence has doubled in most countries over the past 30 years. Researchers also estimated that having a high BMI accounted for 4 million deaths globally, 40% of which occurred in people who were overweight but not yet obese.

This demonstrates that being overweight may almost be as risky to health as being obese. The rate of increase in obesity was also greater in children, showing the need for interventions to halt and reverse this trend to avoid future disease and deaths.

What is considered a healthy weight – BMI 20 to 25 – was unsurprisingly found to be the category with the lowest health risk. The best way to obtain and maintain a healthy BMI is to eat a healthy calorie-restricted diet and exercise regularly; two concepts that are at the core of the NHS Weight Loss Plan.

Where did the story come from?

The study was carried out by researchers from a wide range of global institutions and universities, but was led by the Institute for Health Metrics and Evaluation (IMHE), based at the University of Washington in Seattle. It was funded by the Bill and Melinda Gates Foundation.

The research was published in the peer-reviewed The New England Journal of Medicine on an open-access basis, which means it is free to read online (PDF, 2.3Mb).

A surprising key finding, as the BBC reported, is that "of the 4 million deaths attributed to being overweight in 2015, nearly 40% were not considered clinically obese". The BBC accurately explains how merely being overweight, and not just obese, can increase risk of death.

What kind of research was this?

This was a review and report of evidence from around the world that looked at how the prevalence of being overweight and obese has changed over time. The researchers then looked at how being overweight affects the risk of various health outcomes, including cardiovascular disease and death.

Gathering high quality data from across many studies over time is the best way to see whether prevalence has changed and to see which health conditions are most strongly related to high body mass index (BMI). However, it is difficult to know how big a role BMI plays in raising your risk of certain health conditions, as other factors also have an influence.

What did the research involve?

The researchers analysed data from 68.5 million people from 195 countries looking at the burden of disease related to BMI between 1990 and 2015, and according to age, sex, and country. They looked at both children and adults.

Disease burden was defined as deaths and disability-adjusted life years (accounting for years of life lost or lived with disability) due to high BMI.

Information on adult BMI was provided by 1,276 unique sources from 176 countries, and 1,211 sources from 173 countries provided data on children's BMI.

For adults, "overweight" was defined as a BMI between 25 and 29 and "obese" was 30 or above. In children, the International Obesity Task Force definitions of childhood overweight and obesity were used. These definitions are based on the principle of a child being heavier for their age than you would expect. The results were broken down by sex and by 5-year age groups.

They looked at the effect of high BMI on health outcomes and estimated the increase in risk associated with a change of five units of BMI in 5-year age groups for:

ischemic heart disease (eg angina and heart attack)

ischemic stroke (caused by a blood clot)

haemorrhagic stroke (caused by a bleed)

hypertensive heart disease (strain on the heart caused by high blood pressure)

diabetes

To understand where most of the burden of disease occurs, they looked at three ranges of BMI (20 to 24; 25 to 29 and 30 or over) and for five overarching groups of diseases:

cardiovascular disease

diabetes

chronic kidney disease

cancers

musculoskeletal disorders

They also determined the BMI associated with the lowest overall risk of death.

What were the basic results?

In 2015, globally 107.7 million children and 603.7 million adults were obese. The prevalence has doubled in more than 70 countries since 1980 and continuously increased in most other countries.

Obesity now affects an estimated 5% of all children and 12% of all adults. In all adult age brackets, prevalence was generally higher among women.

Worldwide findings included:

High BMI contributed to 4 million deaths in 2015 (95% confidence interval [CI] 2.7 to 5.3), representing 7.1% (95% CI 4.9 to 9.6) of all deaths globally.

High BMI contributed to 120 million disability-adjusted life years lost (95% CI 84 to 158).

A total of 39% of the deaths and 37% of the disability-adjusted life years were in people with a BMI of less than 30 (i.e. not obese).

Cardiovascular disease was the leading cause of death and disability-adjusted life years with 2.7 million deaths (95% CI 1.8 to 3.7) and 66.3 million disability-adjusted life years (95% CI 45.3 to 88.5).

Diabetes was the second leading cause and contributed to 0.6 million deaths (95% CI 0.4 to 0.7) and 30.4 million disability-adjusted life years (95% CI 21.5 to 39.9).

A normal BMI of 20 to 25 in adults was associated with the lowest risk of death (the UK defines this as a healthy level).

How did the researchers interpret the results?

The researchers concluded that their study "provides a comprehensive assessment of the trends in high BMI and the associated disease burden. Our results show that both the prevalence and disease burden of high BMI are increasing globally. These findings highlight the need for implementation of multicomponent interventions to reduce the prevalence and disease burden of high BMI."

Conclusion

This impressively large global study demonstrates that the prevalence of obesity is increasing worldwide among both children and adults. It supports what has long been thought, that increased body mass index (BMI) contributes to a range of illnesses and is ultimately responsible for a large number of deaths, particularly from cardiovascular disease.

One potential limitation is the use of self-reported BMI or health outcome data in some of the studies, although the majority used a specific independent measurement so this is unlikely to have biased results too much.

It is also always difficult from observational data to be certain of the exact amount of years of life lost or lived with disability that are directly caused by high BMI. It is possible that being overweight or obese may contribute to the risk of getting a particular disease, for example cancer, in combination with other health and lifestyle factors. Therefore, though based on a large quantity of data, the results must still be considered as estimates.

Nevertheless the study highlights what we already know – that being obese is linked to a large number of chronic diseases. Perhaps more notable was that it also shows that almost half of the years of life lost or lived in poor health could be attributed to people being overweight, not just obese.

This study design cannot explain the increasing prevalence of overweight and obesity. However, the fact that obesity has increased in countries of all levels of development indicates it is no longer a problem solely for high income countries. As the authors suggest, there are multiple factors contributing to this continuing trend, including reduced opportunities for physical education with growing urbanisation, along with increased availability, affordability and accessibility of energy-rich but nutritionally poor food.

There is an ongoing need for effective interventions to tackle overweight and obesity, both at the public health and the individual level. Otherwise the public health burden of obesity could be for the 21st Century what smoking was to the 20th Century – an entirely preventable cause of disability and death.

Analysis by Bazian

Edited by NHS Website