A high BMI is not necessarily associated with a higher risk of death

 

BMI (Body Mass Index) is calculated by dividing a person’s weight by the square of their height. For decades, it has been used to assess whether a person’s weight is “healthy” or could bring a risk of diabetes or heart disease. But many health care professionals have criticized this, saying BMI does not account for crucial factors such as body fat percentage and variations in disease risk among people of different races and genders.

Now, the new study found that BMI in the range considered overweight is not linked to a higher mortality risk for many people.

In the study, there was no significant increase in the risk of death for those 65 years and older with BMIs between 22.5 and 34.9. The same was true for younger adults with BMIs between 22.5 and 27.4.

The study compared people with equal BMIs but different waist circumferences and found that the latter was associated with a higher risk of death overall. 

The study results did, however, show that participants with a BMI of 30 or more faced a greater mortality risk. Among younger adults, a BMI of 27.5 to 29.9 was also associated with a nearly 20% greater risk. 

Dr. Fatima Stanford, an obesity medicine specialist at Massachusetts General Hospital, said BMI can equate leanness with health at the expense of other important factors. Substance abuse disorders, tobacco use and disordered eating can all lead to a leaner physique, but do not mean that a person is healthy. 

Stanford also emphasized that the BMI ranges considered overweight or obese do not account for differences that arise among racial and ethnic groups. Some research suggests, for example, that Asian people may face a higher risk of developing metabolic diseases like diabetes and hypertension at a BMI lower than the general thresholds. 

Black women, meanwhile, are often healthy at BMIs in the overweight and obese ranges. And a 2013 study found higher BMI was not as strongly linked to mortality risk in Black Americans as it was in whites. 

However, Dr. Jaime Almandoz, medical director of the Weight Wellness Program at UT Southwestern Medical Center in Dallas, pointed to a few shortcomings in the study. For one, he said, it focuses solely on the relationship between BMI and the risk of death.

“There’s so much more to life than not dying,” Almandoz said. “Studies like this can be misinterpreted by saying, ‘Well, up to a BMI of 30 is fine, or ‘Up to a BMI of 35 in older adults is fine,’ but that doesn’t mean that a person is not living with Type 2 diabetes or an increased risk for heart attack, stroke, heart failure.” 

According to the US Centers for Disease Control and Prevention, people with BMIs of 25 or higher face an increased risk of high blood pressure and cholesterol, Type 2 diabetes and several types of cancer.

Dr. Aayush Visaria, an internal medicine resident at Rutgers Robert Wood Johnson Medical School, said that if the study had looked at participants’ fat percentages, it might have found that more than 27% were obese. But that is precisely the problem. BMI does not measure the share of body fat. 

“This kind of adds to the idea that clinicians should be using different measures of body fat to diagnose obesity, not just BMI,” he said. “I think in the future these measures will become commonplace.”