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Obesity paradox

UK study debunks 'obesity paradox' theory

(Credit: Obesity Action Coalition)
A second study by researchers at Loughborough University has called for an end to the term 'healthy obesity', due to it being misleading and flawed

A study by led by researchers at the University of Glasgow has debunk the notion that people who are overweight or obese are not at increased risk of heart disease, (obesity paradox). The study, which included nearly 300,000 people, shows that the risk of heart attacks, strokes and high blood pressure, increases as BMI increases beyond a BMI22-23. Furthermore, the risk also increases steadily the more fat a person carries around their waist.

The study, ‘The impact of confounding on the associations of different adiposity measures with the incidence of cardiovascular disease: a cohort study of 296 535 adults of white European descent’, published in the European Heart Journal, was conducted in 296,535 adults of white European descent who are taking part in the UK Biobank study. All patients were healthy at the time they enrolled with the study. UK Biobank recruited from 2006 to 2010, and follow-up data on participants were available up to 2015 for this latest analysis.

The research, led by Dr Stamatina Iliodromiti, found that people with a BMI between 22-23 had the lowest risk of cardiovascular disease (CVD). As BMI increased above 22, the risk of CVD increased by 13% for every 5.2 kg/m2 increase in women and 4.3 kg/m2 in men.

Compared to women and men with waist circumferences of 74cm and 83cm respectively, the CVD risk increased by 16% in women and 10% in men for every 12.6cm and 11.4cm increase in waist circumference for women and men, respectively. Similar increases in CVD risk were seen when the researchers looked at waist-to-hip and waist-to-height ratios and percentage body fat mass - all of which are considered reliable ways to accurately gauge the amount of fat a person carries, also known as adiposity.

"Any public misconception of a potential 'protective' effect of fat on heart and stroke risks should be challenged," said Iliodromiti. "This is the largest study that provides evidence against the obesity paradox in healthy people. It is possible that the story may be different for those with pre-existing disease because there is evidence that in cancer patients, for instance, being slightly overweight is associated with lower risk, especially as cancer and its treatments can lead to unhealthy weight loss. By maintaining a healthy BMI of around 22-23 kg/m2, healthy people can minimise their risk of developing or dying from heart disease. In terms of other adiposity measures, the less fat, especially around their abdomen, they have, the lower the risk of future heart disease."

However, the researchers recognise that it can be difficult for some people to maintain a BMI of 22-23, particularly as they get older.

"We know many cannot get to such low BMIs so the message is, whatever your BMI, especially when in the overweight or obese range, losing a few kilograms or more if possible, will only improve your health,” said co-author, Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow. “There are no downsides to losing weight intentionally and the health professions needs to get better at helping people lose weight."

The researchers say their findings may have implications for guidelines on preventing and managing cardiovascular disease.

"Even within the normal BMI category of between18.5-25, the risk of CVD increases beyond a BMI of 22-23,” concluded Iliodromiti. “The other adiposity measures show that the leaner the person the lower the risk of CVD, and this must be a public message, that healthy individuals should maintain a lean physique to minimise their risk of CVD."

The researchers suggest that the previous confusion over the so-called ‘obesity paradox’ may be due to many factors that can confound results of studies. For instance, smoking changes the distribution of fat in the body, smokers may have lower weight as smoking depresses appetites and so BMI tends to be lower. Another reason could be that some people have existing but undiagnosed disease, which can often lower their weight but also makes them more likely to die prematurely.

End the term healthy obesity

A paper by researchers at Loughborough University has called for an end to the term 'healthy obesity', due to it being misleading and flawed. The focus should instead be on conducting more in-depth research to understand causes and consequences of varying health among people with the same BMI. Dr William Johnson, from the School of Sport, Exercise and Health Sciences at Loughborough University, emphasised that the construct of 'healthy obesity', first used in the 1980's to describe obese individuals who were apparently healthy - for example they didn't suffer with hypertension or diabetes, is limited. This is because categorising a population using cut-offs (eg, BMI and blood pressure) results in some normal weight and obese individuals being labelled 'healthy', when there are obviously health differences between the two groups.

In the paper, ‘Healthy obesity: time to give up the ghost?’, published in the Annals of Human Biology, Johnson does acknowledge that there are health differences between obese individuals with the same BMI and explains that there should be further investigation into contributing factors such as being obese for longer, adverse early life events, and smoking during adolescence.

For example, such research would explain why one person has a disease or dies, while another with the same BMI (or waist circumference) is fine.

"While epidemiology has revealed many of the life course processes and exposures that lead to a given disease, we know relatively little about the things that occur across someone's life that lead to them having a heart attack, for example, while their friend with the same BMI is fine. Existing birth cohort studies have the data necessary to improve knowledge on this topic," he claims.

With obesity at epidemic levels worldwide, such research could inform the development of more stratified disease prevention and intervention efforts targeted at individuals who have the highest risk.

“It is undeniable that obesity is bad for health, but there are clearly differences between individuals in the extent to which it is bad,” the authors conclude. “While the concept of healthy obesity is crude and problematic and may best be laid to rest, there is great opportunity for human biological investigation of the levels, causes and consequences of heterogeneity in health among people with the same BMI.”

To access this paper, please click here 

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