The move away from BMI

Last June, the American Medical Association (AMA) voted to adopt a new policy that moves away from solely using BMI when assessing whether a patient is a healthy weight.

In a report, an AMA subcommittee wrote that BMI does not differentiate between fat and lean mass or account for where body fat is located. According to studies, fat that accumulates around the stomach may be more harmful than fat that accumulates in the thighs or legs.

In addition, BMI is primarily based on data from non-Hispanic white populations, which makes it difficult to apply to a broader population. For example, studies have shown that Asian, Hispanic, and Black patients have a higher risk of developing type 2 diabetes at lower BMIs compared to white patients.

Going forward, AMA recommended physicians use BMI in combination with several other factors when assessing patients' health and weight, such as visceral fat levels; body adiposity index; fat, bone, and muscle percentages; and genetic and metabolic factors. The organization also noted that BMI shouldn't be used as a sole criterion for denying insurance reimbursement.

"There are numerous concerns with the way BMI has been used to measure body fat and diagnose obesity, yet some physicians find it to be a helpful measure in certain scenarios," said Jack Resneck, Jr., AMA's immediate past president. "It is important for physicians to understand the benefits and limitations of using BMI in clinical settings to determine the best care for their patients."

Could body composition scans be a better way to gauge health and fitness?

Instead of using BMI, some people are now using body composition scans, which can measure muscle mass and fat distribution, to gauge their overall health and fitness.

MRI scans are considered the gold standard for body composition scans, but they can be difficult to access, partially due to their high cost.

Another type of body composition scan is called DEXA (dual-energy X-ray absorptiometry). DEXA scans measure bone mineral density, body composition, and fat distribution. These scans typically cost over $100, but prices are dropping in some areas as demand increases and more machines become available for use.

An option that has become popular in gyms and workout studios is bioelectric impedance analysis, which is performed by InBody or Evolt 360 devices. Compared to MRI or DEXA scans, these devices are often free to use with a membership or can be used for a small fee.

The devices send a low-level electrical current through the body to estimate fat and lean mass. Although bioelectric impedance analysis is not as precise as an MRI or DEXA scan, it can reliably track changes over time if used correctly.

"The InBody scan is the first tool I've ever used that shows gains," said Mana Mostatabi, recalling her fitness declining during the pandemic. Before, Mostatabi would regularly weigh herself and feel frustrated when the scale didn't change. Now, she can tell when she has lost body fat and gained muscle, even if she hasn't lost any weight.

"It's just incredibly empowering," Mostatabi said.

According to Richard Joseph, a physician who specializes in metabolic health at Brigham and Women's Hospital, it can be helpful for people to know their muscle mass, because research has shown that strength can help predict longevity. Muscle loss can also increase the risk of falling, which is a leading cause of death from injury for older adults.

"The risk of frailty really increases exponentially with age," Joseph said. Muscle loss, which is also called sarcopenia, affects around 45% of older adults, particularly women. To prevent muscle loss, strength training can help.

In addition, having too much body fat, especially visceral fat around the stomach, liver, and intestines, can increase the risk of metabolic disease. "It's inflammatory," Joseph said, and can increase the risk of heart disease.

Currently, most Americans would be classified as having "poor fitness" based on standards set by the American College of Sports Medicine, since the average body fat among U.S. adults is 33%. According to the U.S. military, the optimal body fat for military fitness is between 10% and 20% for young men and up to 25% for middle-aged men. For women, the optimal range is 15% to 30% for young women and up to 38% for middle-aged women.

In general, Joseph said that "it's you versus you" when it comes to fitness. Instead of focusing on an external benchmark, he said that "it's most important to look at trends over time" in your body composition. (Aubrey, "Shots," NPR, 6/3)

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