Obesity-related health evaluations must include waist circumference
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Clinicians should evaluate waist circumference in addition to BMI when determining obesity-related cardiometabolic risks, according to a consensus statement published in Nature Reviews Endocrinology.
“Obesity is an issue, but not all shapes of obesity present the same risk. The addition of waist circumference to BMI allows practitioners a simple, cost-effective way to assess the high-risk phenotype of obesity,” Robert Ross, PhD, professor of exercise physiology in the School of Kinesiology and Health Studies at Queen’s University in Kingston, Ontario, Canada, told Healio. “If you’re simply measuring body weight and dividing by height to indicate to your client’s or your patient’s level of obesity-related risk, your job is not done. You need to add waist circumference.”
Ross and colleagues, who represent a combined group of experts from the International Atherosclerosis Society and the International Chair on Cardiometabolic Risk Working Group on Visceral Obesity, said the recent increase in obesity prevalence has paralleled increases in waist circumference more than BMI.
“Obesity prevalence levels ... based on some surveys [have] been leveling off,” Ross said. “Based on weight-to-height BMI, that seems to be true, although I would say they’re leveling off at some extraordinarily high numbers. But waist circumference is not [leveling off]. ... In other words, [high] waist circumference prevalence is increasing disproportionately to BMI.”
Aging is a major cause of this obesity phenotype, according to Ross. As people age, they may develop greater waist circumference with lower body weight.
“So older adults ... their waistline is going up, and the muscle mass and lower body fat is going down. Sometimes you’re fooled by the bathroom scale,” Ross said.
A more accurate evaluation metric than BMI alone is needed.
“The failure of BMI to detect such an increase in abdominal obesity confirms the limitations of BMI alone to identify the phenotype of obesity that conveys the greatest health risk,” the consensus authors wrote.
Waist circumference enhances efficiency
The authors reviewed research pertaining to both waist circumference and BMI in relation to morbidity and mortality risk and found that “waist circumference is associated with health outcomes within all BMI categories.”
“The combination of BMI and waist circumference can identify the highest-risk phenotype of obesity far better than either measure alone,” the authors wrote. “Waist circumference could be just as important, if not more informative, in persons with lower BMI, where an elevated waist circumference is more likely to signify visceral adiposity and increased cardiometabolic risk.”
Although more study is needed to determine why elevated waist circumference has such an impact on cardiometabolic risk, researchers have proposed several theories, according to Ross.
“What is the mechanism that explains its association with morbidity and mortality?” Ross said. “That the association is there is unambiguous, and their mechanisms are still being worked out. Many think the putative mechanism is that waist circumference is a surrogate for intra-abdominal or visceral obesity.”
The authors highlighted two acceptable techniques from WHO and NIH for measuring waist circumference. WHO advises measurements taken above the iliac crest and below the rib cage whereas the NIH advises measurement at the upper border of the iliac crest. Clinicians — and anyone at home — can implement either of these techniques.
The authors also noted that waist circumference may not substantially improve cardiometabolic risk prediction, but that it can play a major role in reducing risk itself.
“Whether waist circumference adds to the prognostic performance of cardiovascular risk models awaits definitive evidence,” the authors wrote. “However, waist circumference is now clearly established as a key driver of altered levels of cardiometabolic risk factors and markers. Consequently, reducing waist circumference is a critical step in cardiometabolic risk reduction.”
How to reach healthier cutoffs
Exercise is one of the most effective techniques for reducing waist circumference, according to the authors, but increasing exertion may not make big a difference.
“Current evidence suggests that increasing the intensity of exercise interventions is not associated with a further decrease in waist circumference,” the authors wrote.
The ideal strategy involves a combination of increased amounts of physical activity and calorie restriction, according to Ross.
Finding the right target waist circumference is an ongoing discussion. The standard criterion for elevated waist circumference for women is more than 88 cm and for men is more than 102 cm, but these are insufficient, especially when assessing patients of different ethnicities, Ross said.
“We don’t yet have the level of evidence that we need to be absolutely certain that current values that we’re using are optimal. One makes no apologies for that in clinical medicine. We often refine values that we use for biomarkers or for risk factors when new evidence appears. The values that we put forth are the best values that we have right now,” Ross said.
“We need to stratify those who are at the highest risk, and we can do that very simply. We, our consensus panel, are at an absolute loss to understand why there is resistance to include this measure in routine practice,” Ross said. “It’s beyond reason that we don’t take the addition of this tool seriously as a means to improve patient management. That’s ultimately what you want to do.” – by Phil Neuffer
Disclosures: Ross reports no relevant financial disclosures. Please see the statement for all other authors’ relevant financial disclosures.
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