Measuring waist circumference is tricky
Although WHtR looks promising as a substitute for or add-on to BMI, it has its own limitations, particularly the challenge of accurately measuring waist circumference.
Measuring waist circumference “not only takes more time but requires the assessor to be well trained about where to put the tape measure and making sure it’s measured at the same place each time,” even when different people take serial measurements from individual patients, noted Dr. Wee. Determining waist circumference can also be technically difficult when done on larger people, she added, and collectively these challenges make waist circumference “less reproducible from measurement to measurement.”
“It’s relatively clear how to standardize measurement of weight and height, but there is a huge amount of variability when the waist is measured,” agreed Dr. Almandoz. “And waist circumference also differs by ethnicity, race, sex, and body frame. There are significant differences in waist circumference levels that associate with increased health risks” between, for example, White and South Asian people.
Another limitation of waist circumference and WHtR is that they “cannot differentiate between visceral and abdominal subcutaneous adipose tissue, which are vastly different regarding cardiometabolic risk, commented Ian Neeland, MD, director of cardiovascular prevention at the University Hospitals Harrington Heart & Vascular Institute, Cleveland.
The imaging option
“Waist-to-height ratio is not the ultimate answer,” Dr. Neeland said in an interview. He instead endorsed “advanced imaging for body fat distribution,” such as CT or MRI scans, as his pick for what should be the standard obesity metric, “given that it is much more specific and actionable for both risk assessment and response to therapy. I expect slow but steady advancements that move away from BMI cutoffs, for example for bariatric surgery, given that BMI is an imprecise and crude tool.”
But although imaging with methods like CT and MRI may provide the best accuracy and precision for tracking the volume of a person’s cardiometabolically dangerous fat, they are also hampered by relatively high cost and, for CT and DXA, the issue of radiation exposure.
“CT, MRI, and DXA scans give more in-depth assessment of body composition, but should we expose people to the radiation and the cost?” Dr. Almandoz wondered.
“Height, weight, and waist circumference cost nothing to obtain,” creating a big relative disadvantage for imaging, said Naveed Sattar, MD, professor of metabolic medicine at the University of Glasgow.
“Data would need to show that imaging gives clinicians substantially more information about future risk” to justify its price, Dr. Sattar emphasized.
BMI’s limits mean adding on
Regardless of whichever alternatives to BMI end up getting used most, experts generally agree that BMI alone is looking increasingly inadequate.
“Over the next 5 years, BMI will come to be seen as a screening tool that categorizes people into general risk groups” that also needs “other metrics and variables, such as age, race, ethnicity, family history, blood glucose, and blood pressure to better describe health risk in an individual,” predicted Dr. Bessesen.
The endorsement of WHtR by NICE “will lead to more research into how to incorporate WHtR into routine practice. We need more evidence to translate what NICE said into practice,” said Dr. Sattar. “I don’t think we’ll see a shift away from BMI, but we’ll add alternative measures that are particularly useful in certain patients.”
“Because we live in diverse societies, we need to individualize risk assessment and couple that with technology that makes analysis of body composition more accessible,” agreed Dr. Almandoz. He noted that the UT Southwestern weight wellness program where he practices has, for about the past decade, routinely collected waist circumference and bioelectrical impedance data as well as BMI on all people seen in the practice for obesity concerns. Making these additional measurements on a routine basis also helps strengthen patient engagement.
“We get into trouble when we make rigid health policy and clinical decisions based on BMI alone without looking at the patient holistically,” said Dr. Wee. “Patients are more than arbitrary numbers, and clinicians should make clinical decisions based on the totality of evidence for each individual patient.”
Dr. Bessesen, Dr. Wee, Dr. Powell-Wiley, and Dr. Almandoz reported no relevant financial relationships. Dr. Neeland has reported being a consultant for Merck. Dr. Sattar has reported being a consultant or speaker for Abbott Laboratories, Afimmune, Amgen, AstraZeneca, Boehringer Ingelheim, Eli Lilly, Hanmi Pharmaceuticals, Janssen, MSD, Novartis, Novo Nordisk, Pfizer, Roche Diagnostics, and Sanofi.
A version of this article originally appeared on Medscape.com.