‘Fat But Fit’ Simply an Illusion

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, The Independent reported.

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.

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.

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.