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Study suggests exercise may mitigate heart disease risk if you’re overweight, but a lot of caveats are attached

Before anybody jumps to the “we can be both fat and healthy” conclusion, it’s important to consider the study’s limitations.

After analyzing all that data, the researchers found that the people in the study who were overweight or obese were not more likely to have a heart attack or stroke than their peers who were of normal weight.
REUTERS/Rick Wilking

Carrying excess weight has long been associated with an increased risk of cardiovascular disease, including heart attack and stroke. But if you are overweight or obese and you exercise regularly and frequently, you may be able to mitigate that increased risk, according to a new study from the Netherlands.

Specifically, the study found that middle-aged and older people who were overweight or obese but who averaged at least four hours a day of moderate physical activity had the same risk of cardiovascular disease during a 15-year period as people whose weight fell within the “normal” range and who had similar activity patterns.

Now, some headline writers have been claiming that the study means we can be both “fat and healthy.” That’s a big leap to make. For this study, while interesting, comes with all sorts of caveats, which I’ll get to in a minute.

Study details

For the study, researchers at Erasmus University Medical Centre in the Netherlands, analyzed up to 15 years of data collected from 5,344 people aged 55 and older living in Rotterdam. All were participants in the long-running, government-funded research project known as the Rotterdam Study. The data included the participants’ body mass index (BMI), physical activity levels, diet, education, family history of heart disease, alcohol use and smoking habits. 

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The researchers categorized the participants by BMI, dividing them into groups of normal weight (BMI of 18.5 to 24.9), overweight (BMI of 25.0 to 29.9) and obese (BMI of 30 or higher). People considered underweight (BMI of less than 18.5) were excluded from the study, as were those who had diagnosed heart disease when they enrolled in the Rotterdam Study.

The participants were also divided into two physical activity groups, based on the average amount of moderate physical activity (the equivalent of brisk walking) they reported. People in the “high” group averaged four hours of moderate physical activity daily, while those in the “low” group averaged two hours.

The researchers then looked to see how weight and physical activity levels affected the participants’ risk of developing heart disease or stroke over a 10- to 15-year period, after taking into account various confounding factors, such as smoking and diet and family medical history.

Key findings

After analyzing all that data, the researchers found that the people in the study who were overweight or obese were not more likely to have a heart attack or stroke than their peers who were of normal weight. When the researchers plugged physical activity levels into their analysis, however, they observed some interesting correlations.

They found that people in the “low” activity group who were overweight or obese were about a third more likely (33 percent and 35 percent, respectively) to develop heart disease or stroke than their normal-weight peers in the “high” activity group.

But they also found that no matter what people weighed, those in the “low” activity group had a higher risk of heart attack or stroke (about 22 percent higher) than those in the “high” activity group.

“Our findings suggest that the beneficial impact of physical activity on [cardiovascular disease] might outweigh the negative impact of body mass index among middle-aged and elderly people,” the study’s authors write.

A list of limitations 

Before anybody jumps to the “we can be both fat and healthy” conclusion, it’s important to consider the study’s limitations. To begin with, it’s observational, which means it can’t prove that exercise was responsible for lowering the risk of cardiovascular disease.

And there are other important limitations to this study, as the experts who reviewed its findings for the United Kingdom’s National Health Service’s “Behind the Headlines” website point out:

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People are more likely to be physically active when they are in good health, so lower levels of physical activity might suggest people are already unhealthy, and therefore more at risk of heart attack or stroke.

The amounts of exercise people reported are strikingly high. The study didn’t measure activity through monitoring devices, so we can’t be sure that people didn’t overstate how much activity they were doing.

The study included physical activity for transport as well as leisure, so one possibility is that people in Rotterdam get around on foot or bicycle a lot (a factor that may be more significant in the Netherlands than the UK [or the United States]). 

In other words, these findings may not be applicable to other populations, including here in the U.S. 

Many other risks 

“As people often say, if exercise was a medicine, it would be hailed as a miracle cure,” write the NHS reviewers. “This study suggests that what we already know about the benefits of exercise may extend to reducing risk of cardiovascular disease for middle-aged and older people, even if they are overweight or obese.”

But it only suggests that finding. It doesn’t prove it.

“While physical exercise is certainly a good thing,” the NHS reviewers stress, “we can’t be sure that it completely negates the importance of keeping to a healthy weight.”

Furthermore, “the study only looked at the risk of cardiovascular disease,” they point out. “Other obesity-related conditions were not considered.”

Indeed, another study published last week linked obesity to an increased risk of 11 types of cancer.

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FMI: The study by the Dutch researchers was published in the European Journal of Preventive Cardiology, where it can be read in full online.