How BMI compares to physique fats proportion in figuring out weight problems

How BMI compares to physique fats proportion in figuring out weight problems

Many individuals with “regular” physique mass indexes should be overweight, new analysis suggests.

The examine, which shall be introduced Friday in Chicago at ENDO 2023, the annual assembly of the Endocrine Society, provides to a rising physique of proof that highlights the issues of utilizing BMI to measure weight problems.

Weight problems, within the easiest phrases, refers to when an individual has an extra of fats within the physique.

BMI — which is calculated utilizing an individual’s peak and weight — is the usual approach to decide whether or not somebody has weight problems or is obese. A BMI of 30 and above falls into the overweight class for most individuals; 25 to beneath 30 is taken into account obese. It’s ubiquitously utilized by medical professionals to find out who’s in danger for Kind 2 diabetes and coronary heart illness and who qualifies for anti-obesity medicines and weight reduction surgical procedure. 

How BMI compares to physique fats proportion in figuring out weight problems

In accordance with the brand new examine, BMI misses a number of instances of weight problems. Researchers checked out information from virtually 10,000 U.S. adults collected from 2011 to 2018 and located that nearly 36% had weight problems based mostly on their BMI. Use of a distinct measure of weight problems — an individual’s physique fats proportion — put that determine at 74%. The examine has not but been revealed in a peer-reviewed journal.

“The primary message right here is that we vastly underestimate the prevalence of weight problems utilizing BMI and there are various folks with regular BMI who nonetheless have weight problems,” stated Dr. Aayush Visaria, an inside drugs resident at Rutgers Robert Wooden Johnson Medical College, who led the examine. 

The findings come because the American Medical Affiliation additionally takes steps to maneuver away from relying solely on BMI to evaluate well being and weight problems, citing “quite a few considerations with the best way BMI has been used to measure physique fats and diagnose weight problems.” On Wednesday, it adopted a brand new coverage advising well being care professionals to make use of different measures — resembling the place fats is distributed within the physique, waist circumference and the way a lot of an individual’s weight comes from fats — together with BMI. 

Within the new analysis, Visaria used a number of measures of weight problems along with BMI, together with physique fats proportion and one thing known as android-to-gynoid fats ratio. Right here’s how these completely different instruments stack up. 

How is BMI calculated?

The World Well being Group cutoff for weight problems for most individuals is a BMI of least 30, and not less than 25 for folks of Asian descent. The decrease cutoff is as a result of Asians usually tend to develop obesity-related circumstances, together with hypertension and diabetes, at decrease BMIs, in line with the Nationwide Institutes of Well being. Visaria used a cutoff of 27.5 for Asian adults, which is the usual some medical organizations use as a substitute of 25.

BMI is calculated by dividing an individual’s weight, in kilograms or kilos, by their peak, measured in meters or ft, squared. Its simplicity makes it a particularly accessible device — many on-line calculators enable an individual to easily enter their peak and weight — nevertheless it has limitations.

Particularly, “we’re unsure what that weight is made up of,” stated Dr. Jaime Almandoz, medical director of the Weight Wellness Program at UT Southwestern Medical Middle in Dallas, who was not concerned with the brand new analysis. 

How a lot an individual weighs doesn’t solely depend upon how a lot fats is within the physique; there’s additionally the load of muscle, bone, water and organs. BMI doesn’t parse this out.

“Individuals with the identical BMI, identical pants measurement and identical belt notch have completely different quantities of fats and muscle,” stated Dr. Vijaya Surampudi, an assistant director of the UCLA weight administration program in Los Angeles, who was additionally not concerned with the brand new analysis.

Individuals who have extra muscle and fewer fats burn extra energy whereas at relaxation and are thought of to have a more healthy physique composition, however as a result of muscle additionally weighs greater than fats, a really muscular particular person’s BMI can skew larger. 

“There are folks with BMI over 30 who’re weight lifters who’re truly very wholesome,” Visaria stated.

How is physique fats proportion calculated?

Physique fats proportion appears at how a lot of an individual’s weight comes from fats. 

It may be measured utilizing a kind of X-ray known as a Dexa scan, which may distinguish between bone and mushy tissue, like fats, within the physique.   

Whole physique fats proportion better than or equal to 25% for males, or 32% for females, constitutes weight problems, in line with the American Society of Bariatric Physicians. 

Having the ability to decide how a lot of an individual’s physique is fats makes this measurement extra correct than BMI, however the approach comes with its personal shortcomings. 

Whereas there are much less cumbersome methods than a Dexa scan to calculate physique fats proportion, specialised tools remains to be required. That may embrace particular scales or calipers that pinch and measure the thickness of an individual’s pores and skin folds, each which may be bought to be used at house. Some wearable gadgets are additionally capable of estimate physique fats proportion. 

However these instruments nonetheless go away a key query unanswered: the place is the fats saved in an individual’s physique? 

“The place we retailer fats infers a number of well being penalties,” Almandoz stated. 

How is android-to-gynoid fats ratio calculated?

After which there’s the third measure used within the examine, known as the android-to-gynoid fats ratio. 

The measurement appears at how fats is distributed via an individual’s physique and, importantly, how a lot of that fats is visceral fats. The scan compares the quantity of fats across the stomach (often known as android fats) to the quantity of fats across the hips and thighs (often known as gynoid fats), spitting out a ratio. 

Visceral fats — fats saved deep within the stomach, across the organs — is related to plenty of well being penalties, together with Kind 2 diabetes and coronary heart illness. 

“Whenever you’re eager about physique composition, you need to know your metabolic danger. The massive query right here is, how a lot fats is across the organs,” Surampudi stated. 

Whereas visceral fats carries dangers, fats saved across the legs may very well be protecting in opposition to metabolic illness, Visaria stated.

Though there are not any set tips for weight problems cutoffs utilizing this measurement, he stated, the final rule of thumb is that something over 1.0 constitutes weight problems. 

The android-to-gynoid ratio is just like one other frequent measurement, waist-to-hip ratio, which compares the circumference of an individual’s waist to the circumference of the hips, each of which may be measured with a tape measure. 

Which is finest?

Regardless of BMI being an imperfect device, Almandoz stated, it shouldn’t be utterly thrown out. As an alternative, he stated, new BMI measurements must be fine-tuned to incorporate cutoffs which are tailor-made to not simply completely different sexes, but in addition take an individual’s age and race under consideration. 

“We have to have extra particular BMI cutoffs based mostly on this information so we are able to make the device higher, moderately than saying, ‘it’s not nice so let’s not use it,’” he stated. “The options might not be sensible for medical care in low useful resource settings.” 

Any measurement of physique composition wants to have the ability to join outcomes, whether or not that be the quantity of fats an individual has or the place that fats sits, to particular well being dangers, he stated.

Dr. Jack Resneck Jr., a previous president of the American Medical Affiliation, stated in an announcement that some physicians nonetheless discover BMI “to be a useful measure in sure eventualities.”

“It is vital for physicians to grasp the advantages and limitations of utilizing BMI in medical settings to find out the most effective care for his or her sufferers,” he stated.

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