What is really behind the “obesity paradox”.
It has amazed physicians for years: Significantly too many kilos of body weight, it was said, offer a survival advantage for those affected in the event of cardiac insufficiency. According to this, obese patients with a BMI of 25 or more actually died less often from it. Now, a study shows that another factor is far more important.
ÜApparently, overweight or obese patients with heart failure do not have a survival advantage. According to a study in the “European Heart Journal”, Scottish physicians write that their results invalidate the so-called obesity paradox, which had puzzled experts for years. In addition, the study questions the current body mass index (BMI) as an indicator of the state of health. Excess body fat can be better inferred from the ratio of waist to height, the scientists emphasize.
The obesity paradox states that while people who are overweight or obese have a higher risk of developing heart problems, they are more likely to survive with such conditions than people of normal weight. In order to justify this, physicians had to speculate – for example that additional fat in the case of heart problems could offer protection against further health problems.
However, a team led by cardiologist John McMurray from the University of Glasgow suspected that the BMI was a rather weak indication of how much fatty tissue a patient had. “We knew this couldn’t be true and that obesity had to be bad rather than good,” he says, referring to the obesity paradox.
BMI compares a person’s weight to height. However, it ignores the composition of fat, muscle and bone, and fat distribution. This is what Stephan von Haehling and Ryosuke Sato from the University Hospital Göttingen point out in a comment on the study. “Would it be plausible to assume that an American professional wrestler (more muscle) and a Japanese sumo wrestler (more fat) with the same BMI would have a similar risk of cardiovascular disease?” This also applies to people like actor Arnold Schwarzenegger, who probably had a BMI of around 30 when he was younger – which actually corresponds to being very overweight.
In the study, the team analyzed data from 1,832 women and 6,567 men with a specific form of heart failure. Doctors examined the values for BMI, body measurements and blood pressure as well as the results of blood tests and the medical history. It was also recorded which patients with heart failure came to the hospital and which died as a result.
Obese patients with a BMI of 25 or more actually had fewer deaths. However, this result dissolved when the team also considered other factors. “The paradox was far less obvious when we examined the waist-to-height ratio, and it disappeared after correcting for the prognostic variables,” says lead author Jawad Butt of Copenhagen University Hospital Rigshospitalet.
After this correction, both BMI and waist-to-height ratios showed that more body fat was associated with a higher risk of death or hospitalization. However, this association was even clearer when looking at the waist-to-height ratio: “The 20 percent of people who were the most fat had a 39 percent higher risk of being hospitalized for heart failure than those who were obese fat were in the bottom 20 percent of patients.”
“Our study shows that if we use better methods of measuring body fat, there is no obesity survival paradox,” McMurray concludes. BMI does not take into account the location of fat in the body, nor its amount in relation to muscle or skeletal weight, which can vary by gender, age and ethnicity. Especially in heart failure, fluid accumulation would also contribute to body weight, according to the doctor: “Indicators that do not include weight, such as the ratio of waist to height, have clarified the true relationship between body fat and patient results in our study.”
Whether weight loss could improve prognosis is a question that future studies should examine, McMurray says: “In the UK, the National Institute for Health and Care Excellence now recommends using waist-to-height ratio instead of BMI for the general population.” This should also apply to patients with heart failure.
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