‘Metabolically healthy obese’ are 50% more likely to suffer heart disease than those of normal weight, finds University of Birmingham study

People who are obese run an increased risk of heart failure and stroke even if they appear healthy, without the obvious warning signs such as high blood pressure or diabetes, according to a major new study.

The findings, presented at the European Congress on Obesity in Porto, Portugal, may be the final death knell for the claim that it is possible to be obese but still metabolically healthy – or “fat but fit” – say scientists.

Several studies in the past have suggested that the idea of “metabolically healthy” obese individuals is an illusion, but they have been smaller than this one. The new study, from the University of Birmingham, involved 3.5 million people, approximately 61,000 of whom developed coronary heart disease.

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The issue has been controversial. Obesity is usually measured by body mass index (BMI) – a ratio of weight against height. It is generally agreed to be imperfect because athletes and very fit people with dense muscle can have the same BMI as somebody who is obese.

The scientists examined electronic health records from 1995 to 2015 in the Health Improvement Network – a large UK general practice database. They found records for 3.5 million people who were free of coronary heart disease at the starting point of the study and divided them into groups according to their BMI and whether they had diabetes, high blood pressure [hypertension], and abnormal blood fats [hyperlipidemia], which are all classed as metabolic abnormalities. Anyone who had none of those was classed as “metabolically healthy obese”.

The study found that those obese individuals who appeared healthy in fact had a 50% higher risk of coronary heart disease than people who were of normal weight. They had a 7% increased risk of cerebrovascular disease – problems affecting the blood supply to the brain – which can cause a stroke, and double the risk of heart failure.

Dr Rishi Caleyachetty, who led the study, said it was true that weightlifters could be healthy and yet have a BMI that suggested they were obese. “I understand that argument. BMI is crude … but it is the only measure we have in the clinic to get a proxy for body fat. It is not realistic [to use anything else] in a GP setting or in the normal hospital clinic. We have to rely on BMI measurements, however crude they may be,” he said.

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While BMI results for particular individuals could be misleading, the study showed that on a population level, the idea that large numbers of people can be obese and yet metabolically healthy and at no risk of heart disease was wrong.

Caleyachetty said: “The priority of health professionals should be to promote and facilitate weight loss among obese persons, regardless of the presence or absence of metabolic abnormalities.

“At the population level, so-called metabolically healthy obesity is not a harmless condition and perhaps it is better not to use this term to describe an obese person, regardless of how many metabolic complications they have.”

Last August a study from Sweden, which followed 1.3 million men over 30 years, found that those who were the fittest when they were 18 years old were 51% less likely to die prematurely than those who were the least fit. But if the men were obese, that cancelled out the advantage they had from their fitness in their youth.

Professor Peter Nordstrom, who led the study published in the International Journal of Epidemiology, said at the time: “These results suggest low BMI early in life is more important than high physical fitness with regard to reducing the risk of early death.”

Professor Timothy Gill from the Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders at the University of Sydney, Australia, said that there would always be some people who remain healthy in spite of obesity, just as there are some lifetime smokers who do not get lung cancer.

“I think you can argue that there are still likely to be some people who are not going to suffer the ill-health consequences as much as other people just because of the distribution of risk,” he said.

The World Obesity Federation has this month officially recognised obesity as a disease because of the wide variety of health problems associated with it.

Susannah Brown, senior scientist at World Cancer Research Fund, said the study’s finding, “emphasise the urgent need to take the obesity epidemic seriously.

“As well as increasing your risk of cardiovascular disease, being overweight or obese can increase your risk of 11 common cancers, including prostate and liver. If everyone were a healthy weight, around 25,000 cases of cancer could be prevented in the UK each year.”