The American obesity epidemic may be even worse than experts believe, according to a new report from the New York University School of Medicine. The Centers for Disease Control (CDC) cites that 35 percent of American adults and 17 percent of American children are obese. However, this new research found that using Body Mass Index (BMI) to calculate obesity rates may be missing almost 40 percent of obesity cases. Because BMI is a rough estimate of body fat using a person’s height and weight, it cannot directly measure body fat. Using this measurement may be categorizing people who have lost muscle mass as overweight, rather than obese, as they should be classified. Losing muscle mass is particularly common in post-menopausal women.
The NYU researchers used BMI and two other measures in their study of a nationally-representative cross section of 1,400 people. The other measures were levels of leptin, which is a protein that regulates metabolism, and Dual Energy X-Ray Absorptiometry (DXA), which tests muscle mass, body fat, and bone density. The key finding was that 39 percent of the participants were misclassified as non-obese using BMI, but were considered obese using a DXA test to directly and more accurately measure their body fat. In women, the percentage of misclassified participants was even higher – at 50 percent.
So, if BMI is underestimating the obesity problem, why is it still so commonly used? It has become so prevalent mainly because it the data to calculate BMI is so inexpensive and easy to collect – all it requires is a person’s height and weight. The researchers explain, however, that both leptin measurement and DXA tests are becoming less expensive. Dr. Robin Blackstone, president of the American Society for Metabolic & Bariatric Surgery (ASMBS), said that she thinks that the study confirms what a lot of physicians believe: BMI should not be used as a strict cut off for who should be treated for obesity. “A lot of the literature from the NIH and CDC reflects an older point of view, but now we have a shifting paradigm. There shouldn’t be an arbitrary [BMI] cutoff before someone considers treatment,” she concluded. Blackstone also explained that many physicians are now using Body Adiposity (body fat) Index, which measures a person’s hip circumference and height and is just as inexpensive as BMI, but research has shown it to be more accurate.
We spoke with Dr. Val Andrei, expert bariatric surgeon in New Jersey, about the article. He told us that the information presented in this article once again points out that in treating or controlling the co-morbidities secondary to obesity, one needs to directly and more accurately measure patients’ body fat (such as with DXA). He said: “Until different modalities will be accepted by managed care companies, these additional measurements would especially be important in patients with BMI lower than 35, who will benefit in the treatment of co-morbidities such as Diabetes and/or Hypertension. In addition, using the Height and Hip Circumference measurement more and more (during our daily evaluations) and correlating it with severe co morbidities of obesity will help the medical community to support our patients that are not “candidates” to undergo weight loss surgery based on BMI values,” Andrei concluded.
You can read more about BMI and on-going research about measuring obesity here.
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