Weight and Watch: How high BMI is no longer linked to higher risk of death

The health effects of being “overweight” might not be all that harmful. According to a recent study, having a body mass index (BMI) in the range that is deemed overweight or even obese is not always linked to an increased risk of dying. The study underscores the limitations of BMI, long a standard medical metric for predicting people’s health. Let’s take a closer look. Also read: How much is too much? Does obesity change the way your brain views food? What does the study say? The findings, published on Wednesday in the journal PLOS ONE, come as populations in both rich and poor countries are becoming heavier. In the United States, more than 70 per cent of adults are defined as either overweight or obese. The new study assessed the relationship between BMI and the risk of death from any cause, based on data from more than 550,000 non-pregnant Americans older than age 20 from the 1999-2018 National Health Interview Survey and the 2019 US National Death Index. “The real message of this study is that overweight as defined by BMI is a poor indicator of mortality risk and that BMI, in general, is a poor indicator of health risk and should be supplemented with information such as waist circumference, other measures of adiposity (fat), and weight trajectory,” lead study author Dr Aayush Visaria, an internal medicine resident physician at the Rutgers Robert Wood Johnson Medical School in New Brunswick, New Jersey told CNN. According to the findings, there was no significant rise in the risk of death among people 65 years and older with BMIs between 22.5 and 34.9. The same held true for people aged 20 to 65 with BMIs ranging from 24.5 to 27.4. Also read: Explained: How women’s PCOS condition can affect their sons Waist circumference is a crucial metric The American Medical Association this month established a policy encouraging doctors to utilise new metrics, such as waist circumference, body fat distribution, and hereditary markers, to evaluate a patient’s health. The study’s findings, according to Dr Visaria, support the revised recommendations. Measuring waist circumference or performing a type of scan that visualises bone density, body fat and muscle mass should also be used for a more holistic interpretation, he said. Having excess fat still increases the risk for a range of conditions including heart disease, stroke and diabetes, reported AFP. “People with elevated waist circumference had a higher risk of mortality compared to normal waist circumference within the same BMI groups. In the overweight BMI range (25-29.9), the risk of mortality was 17 to 27 per cent higher among people with elevated waist circumference compared to lower waist circumference,” Visaria told CNN in an email. Also read: A Big Fat Problem: How more than half the world is set to become obese and why this is dangerous About BMI BMI, which was first described by a Belgian mathematician in the 19th century, is calculated by dividing a person’s weight by the square of their height. It is increasingly seen as a crude instrument for measuring individual health. The US Centres for Disease Control and Prevention define an adult’s “overweight” status as a BMI between 25 and 29.9 and a “healthy” or “normal” weight as a BMI between 18.5 and 24.9. Obesity is defined as having a BMI of more than 30. It rose to prominence for clinicians in the 1990s following the World Health Organization’s adoption of the metric as the official screening index for obesity. The amount of body weight that is made up of body fat may have a substantial link with BMI in studies of averages of large populations of people, but it does not directly assess body fat for an individual. In light of several variables like age, muscular mass, sex, and race, people with the same BMI may have significantly varying body fat percentages. Since it does have a role in a full workup, BMI may still be used in clinical practice as a marker of potential health risk, but it shouldn’t be the sole one, according to Dr Visaria. Also read: Obesity is gateway to serious health issues, here’s how you can keep it at bay The risk of death from obesity still remains higher The risk of developing a disease, on the other hand, is “probably a more important measure of health than all-cause mortality,” according to CNN quoted Tom Sanders, professor emeritus of nutrition and dietetics at King’s College London, who was not involved in the study, as saying. “The main hazard of overweight and moderate obesity is a three times greater risk of developing diabetes which contributes to cardiovascular disease, renal failure and blindness,” he said in a statement. For example, a person with “third degree” obesity, defined as a BMI of 40 or above, but had never smoked and had no history of cardiovascular disease or non-skin cancer, was more than twice as likely to die as an equivalent counterpart with BMI defined as average. The visceral or belly fat that surrounds the body’s organs has been associated with heart disease, frailty, and early death in both sexes as well as a 39 per cent increased risk for dementia in older women. A waist circumference of 40 inches (102 centimetres) or more for men and 35 inches (88 centimetres) or more for women is considered to be abdominal obesity. “It’s a large study with a representative sample which is good,” George Savva, a biostatistician at the Quadram Institute in the United Kingdom, told AFP. “The authors have, as far as I can see, done a good job of analyzing the mortality link with baseline weight status.” He added it might be the case that diseases linked with higher weight are managed better than they once were, for example, high blood pressure and high cholesterol. “So you would expect the relationship between weight and death to change over time, which potentially is what this is showing,” Savva said. With inputs from AFP and The Conversation