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Step aside BMI, body composition tests are on the rise. Here's what to know

Maria Fabrizio

The scale has never been a friend to Mana Mostatabi. Even back in high school, when she ran a quick 100m on the varsity track team, her BMI 鈥 a ratio of weight to height 鈥 put her in the overweight category.

鈥淢y dad always joked that I should be a wrestler,鈥 Mostatabi says due to her build. Many Some are considered obese despite their fitness, and many doctors say it isn鈥檛 a helpful metric to focus on.

鈥淏MI is a very crude measure,鈥 says , a physician at Brigham and Women鈥檚 Hospital who specializes in metabolic health. 鈥淚t doesn鈥檛 tell me much about your underlying health,鈥 he says. People can be a normal weight but have low muscle mass and high body fat, while others have higher body weight but are muscular and lean.

That鈥檚 why Mostatabi has found a new tool 鈥 a 鈥 that measures her body fat and muscle mass, which are two key metrics of health. 鈥淚t鈥檚 very affirming,鈥 Mostatabi says. Over the last year, she has lost ten pounds of body fat and also gained several pounds of muscle. 鈥淭his actually gives me information,鈥 to track progress. 鈥淚t really is motivating,鈥 she says.

Body composition scans are becoming an increasingly popular way to gauge health and there are lots of different kinds.

An MRI () is considered the gold standard, but it鈥檚 not practical for most people given the expense and access to medical imaging.

Dr. Joseph orders DEXA 鈥 鈥 scans for some of his patients. These scans measure bone mineral density, and also measure body composition and fat distribution. They typically cost more than $100, but in some areas as demand rises and more machines are available.

An option that鈥檚 taken off in gyms and workout studios, such as and is bioelectric impedance analysis, using devices such as the or the . Depending on the studio, the scans are often free with membership or are available for a small fee. This test is not as precise as an MRI or DEXA, but is reliable at tracking changes over time, as long as people follow directions.

Mana Mostatabi uses a body composition test to track her fitness. It's helped her lower her body fat and increase muscle.
Mana Mostatabi /
Mana Mostatabi uses a body composition test to track her fitness. It's helped her lower her body fat and increase muscle.

Mostatabi had her first scan in January, when she signed up for a strength challenge at Orangetheory. 鈥淚t鈥檚 a super simple process,鈥 Mostatabi says, which takes less than a minute.

The device looks like a scale with two arms. 鈥淵ou step onto the machine,鈥 which has a metal base, she explains and you hold onto the ends of the two arms which send a safe, low-level electrical current through the body, estimating fat and lean mass.

鈥淗ow fast that current is returning to the electrodes gives a measurement of how much fat mass and muscle you have, because the current travels through those body tissues at different speeds,鈥 explains Scott Brown, Vice President of fitness at Orangetheory. The technology is , and has become increasingly popular with the advent of commercial devices and rising demand.

Mostatabi says you can鈥檛 feel anything during the test, and the results are sent directly to a smart phone app. Her first scan gave her a benchmark to improve upon.

She explains her fitness took a nosedive during the pandemic, and she was aiming for a fresh start this year. All winter she pushed herself through 60 minute classes that combined resistance training, weight lifting, cardio on a treadmill and rowing. 鈥淚 was very diligent,鈥 averaging about five to six classes per week.

鈥淭he InBody scan is the first tool I鈥檝e ever used that shows gains,鈥 she says. Mostatabi was accustomed to weighing herself, and recalls the frustration when the scale would not budge. Now, even if she hasn鈥檛 lost weight, she knows her body is healthier, with a lower percentage of body fat and an increase in muscle.

鈥淚t鈥檚 just incredibly empowering,鈥 she says, knowing that women who weight train and build strength can and healthier lives.

On average, women gain less muscle at a slower rate compared to men. During Orangetheory鈥檚 eight week 鈥榯ransformation challenge鈥 the company found that males who were focused on muscle gains added about .83 lbs of muscle over eight weeks, on average, compared to a half pound of muscle gain for females. Though across all participants there was only about .1 lb of average muscle gain.

Eight weeks is not a lot of time to gain muscle, explains Brown. And he says it鈥檚 important to set 鈥渞ealistic goals and targets'' given the variability from person to person. The ability to build new muscle is influenced by gender, age and genetics.

Dr. Joseph says the reason it can be helpful to know your muscle mass is because studies show that strength is a predictor of longevity. Also, loss of muscle increases the risk of falling, which is a from injury among older people. 鈥淎 lot of people are under-muscled,鈥 Joseph says.

When it comes to body fat, having too much can increase the risk of metabolic disease, especially , which surrounds the abdominal organs including the stomach, liver and intestines. 鈥淚t鈥檚 inflammatory,鈥 Joseph says and drives up the risk of heart disease. The American College of Sport Medicine sets for body fat based on age and gender, but there isn鈥檛 not an agreed upon target for what鈥檚 considered ideal. Using the ACSM standards, most Americans could be classified in the 鈥減oor fitness鈥 category, as the among adults in the U.S. is 33%. The U.S. military considers the for military fitness to be between 10% and 20% for young men and up to 25% for middle-aged men. Women typically have more body fat, with an ideal range from 15% to 30% for young women and up to 38% for middle-aged women.

Joseph says the rule of thumb for fitness is that 鈥渋t鈥檚 you versus you.鈥 Rather than fixate on an external benchmark, 鈥渋t鈥檚 most important to look at trends over time,鈥 in your body composition, he says.

It鈥檚 possible to lose fat and gain muscle, without losing any weight. This is what happened to , who is 59, and a certified health coach in Alexandria, Virginia. She鈥檚 gained about three pounds of muscle over the last three years, and has shed body fat,too. Her body fat has dropped from 26% down to 22%. 鈥淟iterally, I鈥檓 the exact same weight,鈥 after three years of tracking, but the positive changes in her body composition are profound.

 Karen White is a certified health coach in Alexandria, Virginia. She credits body composition tests with helping her reduce body fat and build muscle.
Jackie Cooke /
Karen White is a certified health coach in Alexandria, Virginia. She credits body composition tests with helping her reduce body fat and build muscle.

She lifts weights three times a week, for about 30 minutes and has progressively built up to lifting heavier weights. She still does cardio work-outs and stays active with daily walks with her dog, though she has shifted her focus to resistance training.

鈥淭he misperception is that older people can't gain muscle, and that's absolutely not true,鈥 she says. She points to a new client she鈥檚 working with in her 60s. Already, after a few months, her client has lost body fat and increased her strength.

White agrees that it鈥檚 important to set realistic expectations, and recognize the changes in body composition may take time. She has gained about a pound of muscle per year, on average, and feels a lot stronger.

Given that muscle peaks in our 30s, it鈥檚 important to do strength-training to maintain muscle mass, especially as we age. 鈥淭he risk of frailty really increases exponentially with age,鈥 Dr. Joseph says and muscle-loss, affects an estimated 45% of older adults, especially women. can help fend off this loss.

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This story was edited by

Copyright 2024 NPR

Allison Aubrey is a correspondent for NPR News, where her stories can be heard on Morning Edition and All Things Considered. She's also a contributor to the PBS NewsHour and is one of the hosts of NPR's Life Kit.