Even ‘metabolically healthy’ obese people have higher heart disease risk

People who are considered metabolically healthy may still have a higher risk of developing heart problems if they are obese than they would if they weighed less, a recent study suggests. 

Obesity on its own is a risk factor for heart disease. The study focused on the odds of heart problems for people at various weights who were considered metabolically healthy because they did not have three other risk factors for heart disease: diabetes, high blood pressure or elevated cholesterol. 

Metabolically healthy obese people were 49 per cent more likely to develop cardiovascular disease and almost twice as likely to develop heart failure as normal-weight people without any metabolic abnormalities, the study found. 

“Although those `metabolically healthy’ obese people may not have those risk factors we described – diabetes and high blood pressure and blood fats – being obese is already a metabolic abnormality,” said senior study author Neil Thomas of the University of Birmingham in the UK. 

“There is no such thing as `metabolically healthy’ and obese,” Thomas said by e-mail. 

Globally, 1.9 billion adults are overweight or obese, according to the World Health Organisation. Obesity increases the risk of heart disease, diabetes, joint disorders and certain cancers. 

For the study, researchers focused on one commonly used measure of obesity known as body-mass index (BMI), a measure of weight relative to height. 

A BMI between 18.5 and 24.9 is considered healthy, 25 to 29.9 is overweight, 30 or above is obese. Anyone with a BMI below 18.5 is considered underweight. 

An adult who is 175cm tall and weighs from 57kg to 76kg would have a healthy weight and a BMI of 18.5 to 24.9, according to the US Centres for Disease Control and Prevention. An obese adult at that height would weigh at least 92kg and have a BMI of 30 or more.

For the current study, researchers examined data on 3.5 million adults who were at least initially free of heart disease. 

Overall, about 3 per cent of these people were underweight without any metabolic abnormalities, 38 per cent were metabolically healthy and at a normal weight, and 26 per cent were overweight without metabolic issues. Another 15 per cent were metabolically healthy and obese. 

Metabolic problems were rare, regardless of people’s weight. 

But like obese people in the study, individuals who were not obese but who were overweight without metabolic abnormalities still had a higher risk of heart disease than people who were metabolically healthy and also at a healthy weight, researchers report in the Journal of the American College of Cardiology. 

Individuals who were underweight and without metabolic abnormalities had a higher risk of vascular disease than people who were a normal weight, the study also found. This might be at least partially explained by smoking, which can mean people are slimmer but also that they have a higher risk of vascular problems, the authors note. 

One limitation of the study is that BMI does not distinguish between weight from fat versus lean muscle mass, making it possible that at least some people classified as obese in the study were actually unusually muscular rather than fat, the authors also point out. The study might also include people who had undiagnosed risk factors for cardiovascular disease. 

People should not base their understanding of their own health and fitness on BMI alone, said Jennifer Bea, a researcher at the University of Arizona in Tucson. 

“You can have a normal BMI, but low muscle tone and low bone mass, thus by default, a high percentage of fat,” Bea said by e-mail. “Even normal weight individuals based on BMI can have metabolic dysfunction and be at risk.”