Study Finds More Accurate Way to Determine Adolescent Obesity

Adam Pope wrote . . . . . . .

The body mass index calculations that physicians have been relying on for decades may not be accurate for assessing body fat in adolescents between the ages of 8 and 17.

A new study published today in the Journal of the American Medical Association Pediatrics shows that tri-ponderal mass index estimates body fat more accurately than the traditional BMI in adolescents.

These new findings are timely as diagnosing, treating and tracking the prevalence of children and adolescents with obesity is a high public health priority. Moreover, many school districts are sending home report cards labeling adolescents as overweight — a practice that has been controversial because children and adolescents tend to be more vulnerable to weight bias and fat shaming than adults.

bmi tmi graphic“Treating obesity in adolescents requires an accurate diagnosis first,” said lead scientist Courtney Peterson, Ph.D., an assistant professor in the School of Health Professions at the University of Alabama at Birmingham. “We found that TMI is both more accurate and easier to use than BMI percentiles. These new findings have the power to potentially change the way we diagnose obesity in children and adolescents ages 8 to 17.”

BMI is the standard used worldwide to screen for obesity in both children and adults, despite prior evidence that it does not work as well in adolescents. To test BMI accuracy in adolescents, researchers compared body composition data from 2,285 Caucasian individuals ages 8 to 29 who participated in the 1999-2004 U.S. National Health and Nutrition Examination Survey (NHANES). Their findings challenge the accuracy of BMI (weight in kilograms divided by height in meters squared) in adolescents and show that TMI (weight divided by height cubed) estimates body fat more accurately than BMI in those 8 to 17 years old.

“BMI is a pretty good tool for determining whether adults are overweight or obese,” Peterson said. “But we’ve always kind of known that it doesn’t work as well in children.”

Using three different calculations — stability with age, accuracy in estimating percent body fat and accuracy in classifying adolescents as overweight versus normal weight — researchers compared BMI to several different obesity indices. They found that TMI is the best overall body fat index to use in Caucasian adolescents between the ages of 8 and 17.

The researchers found that TMI better estimates body fat percentage, especially in male adolescents for whom the investigators found BMI to be particularly inaccurate. Their analysis also showed TMI to be a better index for diagnosing overweight adolescents than the current BMI percentiles. Using BMI percentiles, researchers noted that adolescents are incorrectly diagnosed as overweight 19.4 percent of the time, versus an only 8.4 percent incorrect overweight diagnosis rate for TMI. The data showed this is especially true for lean adolescents, a significant fraction of whom are incorrectly being diagnosed as overweight.

The researchers also used mathematical strategies to show how the relationship between body weight and height is much more complex in children and adolescents than it is in adults, particularly when adolescents are rapidly growing. The authors explained that for decades this complexity made it challenging to figure out the optimal body fat index for adolescents.

Steven Heymsfield, M.D., one of the team’s physician scientists at LSU’s Pennington Biomedical Research Center, added that, to make BMI work in children, complicated BMI percentiles called “Z scores” were developed to diagnose overweight status and obesity based on BMI levels specific to a child’s age and gender. But the researchers found that using percentiles does not solve BMI’s accuracy problems.


“These findings are important. Many school districts send home report cards labeling adolescents as overweight, and children and adolescents tend to be more vulnerable to weight bias and fat shaming than adults.”

— Courtney Peterson, Ph.D.


Peterson mentioned that percentiles are problematic because they change over time and can become outdated. However, she emphasizes that, even if BMI percentiles were updated to be as accurate as TMI for diagnosing adolescents as lean versus overweight, TMI still inherently estimates levels of body fat in adolescents more accurately than BMI does, while also eliminating the need for complicated percentiles.

“These findings are important,” Peterson said. “Many school districts send home report cards labeling adolescents as overweight, and children and adolescents tend to be more vulnerable to weight bias and fat shaming than adults.”

Obesity increases the risk of several chronic diseases in adults, including diabetes, cardiovascular disease and cancer. Children who are overweight are at an even higher risk than adults, and nearly one in six children in the United States is overweight. Several national and global initiatives are underway to screen and diagnose children who are overweight as a first step in curbing the obesity epidemic and the chronic diseases that follow.

Investigators agree that further research is needed to assess the effectiveness of TMI in broader audiences, including wider age ranges and ethnicities.

“We look forward to collaborating with other existing national and global health organizations to analyze additional data for diagnosing weight status among children and adolescents,” Peterson said. “Ultimately, we hope this research lays the foundation for improving the health of adolescents, and we think that down the road TMI will likely replace BMI for children and adolescents.”

Source: University of Alabama at Birmingham


Today’s Comic

It’s Time to Ditch BMI for BVI as a Measure of Obesity

Laura Entis wrote . . . . . .

Body mass index has long determined what it means to be overweight. Invented in the early 1800s by a Belgian statistician, the measurement is used as a definitive benchmark: those with a score below 18.5 are underweight, those who fall between 18.5 and 24.9 are normal, those between 25 to 29.9 are overweight, and those 30 and higher are obese.

For years, medical professionals have taken issue with these cleanly drawn lines. The BMI scale, critics argue, is too simplistic to accurately reflect health on an individual basis.

Today, the Mayo Clinic adds its voice to the chorus. The medical care provider announced that is recommending a new system for measuring body composition and weight distribution: the Body Volume Indicator (BVI). Unlike BMI, which is formulated by comparing an individual’s weight in relation to his or her height, BVI considers “other crucial factors such as fat mass, lean mass, and weight distribution when determining an individual’s body composition,” Jose Medina-Inojosa, a cardiovascular research fellow at the Mayo Clinic, told Fortune. In addition to weight and height, information on waist-to-hip ratio, total body fat percentage, and abdominal volume is factored when determining a score.

These are harder metrics to measure than feet and pounds, of course, but technology has advanced since the 19th century. Select Research, a U.K.-based market research agency and pioneer in 3D body measurement, in cooperative development with Mayo Clinic, has launched an app to help people measure their BVI.

Here’s how it works: doctors take two photos of their patients, wearing just their underwear, from the front and from the side. After the photos are taken, they are turned into 3D body silhouettes, and sent to a backend server where the images are compared to a database compiled from thousands of MRI images, 3D body scans, and Cadaver information. (The photos themselves are then deleted.)

By cross-referencing 3D silhouettes of patients with this database, the app provides more detailed information on weight distribution and volume, particularly for the abdomen, the area of the body “associated with the greatest risk for metabolic disease and insulin resistance,” said Medina-Inojosa. An increasing body of research suggests that fat in the midsection, which blankets the organs, is associated with a higher likelihood of premature mortality than fat carried in other areas of the body. Two women could be the same weight and height, but if one carries most of the weight in her hips, while the other’s is distributed primarily in the stomach, the latter would be at greater risk of developing a host of health issues. Their BMIs would be identical, but because BVI considers weight distribution and the percentage of fat stored in the abdominal cavity, those numbers would be different.

Not only does BVI serve as a more granular measurement, but Medina-Inojosa believes it can also be used as a tool to improve motivation and accountability; it’s possible to gain muscle and change one’s overall body shape, without seeing a similar shift in BMI.Most importantly, however, he hopes a new system will help people realize that “obesity is a complex disease not only defined by weight.” He’d like to see the conversation move beyond a fixation on pounds gained and lost.

Source: Fortune


Today’s Comic

Don’t Use Body Mass Index to Determine Whether People Are Healthy, Study

BMI incorrectly categorizes millions of ‘obese’ people as unhealthy, according to research.

Over the past few years, body mass index, a ratio of a person’s height and weight, has effectively become a proxy for whether a person is considered healthy. Many U.S. companies use their employees’ BMIs as a factor in determining workers’ health care costs. And people with higher BMIs could soon have to pay higher health insurance premiums, if a rule proposed in April by the Equal Employment Opportunity Commission is adopted.

But a new study led by UCLA psychologists has found that using BMI to gauge health incorrectly labels more than 54 million Americans as “unhealthy,” even though they are not. The researchers’ findings are published online today in the International Journal of Obesity.

“Many people see obesity as a death sentence,” said A. Janet Tomiyama, an assistant professor of psychology in the UCLA College and the study’s lead author. “But the data show there are tens of millions of people who are overweight and obese and are perfectly healthy.”

The scientists analyzed the link between BMI — which is calculated by dividing a person’s weight in kilograms by the square of the person’s height in meters — and several health markers, including blood pressure and glucose, cholesterol and triglyceride levels, using data from the most recent National Health and Nutrition Examination Survey.

The study found that close to half of Americans who are considered “overweight” by virtue of their BMIs (47.4 percent, or 34.4 million people) are healthy, as are 19.8 million who are considered “obese.”

Given their health readings other than BMI, the people in both of those groups would be unlikely to incur higher medical expenses, and it would be unfair to charge them more for health care premiums, Tomiyama said.

Among the other findings:

  • More than 30 percent of those with BMIs in the “normal” range — about 20.7 million people — are actually unhealthy based on their other health data.
  • More than 2 million people who are considered “very obese” by virtue of having a BMI of 35 or higher are actually healthy. That’s about 15 percent of Americans who are classified as very obese.

Tomiyama, who directs UCLA’s Dieting, Stress and Health laboratory, also called DiSH, found in previous research that there was no clear connection between weight loss and health improvements related to hypertension, diabetes, and cholesterol and blood glucose levels.

She said she was surprised at the magnitude of the numbers in the latest study.

“There are healthy people who could be penalized based on a faulty health measure, while the unhealthy people of normal weight will fly under the radar and won’t get charged more for their health insurance,” she said. “Employers, policy makers and insurance companies should focus on actual health markers.”

Jeffrey Hunger, a co-author of the paper and a doctoral candidate at UC Santa Barbara, said the research shows that BMI is a deeply flawed measure of health. “This should be the final nail in the coffin for BMI,” he said.

Hunger recommends that people focus on eating a healthy diet and exercising regularly, rather than obsessing about their weight, and strongly opposes stigmatizing people who are overweight.

The proposed EEOC rule would allow employers to charge higher insurance rates to people whose BMI is 25 or higher. A BMI between 18.5 and 24.99 is considered normal, but the study emphasizes that normal BMI should not be the primary goal for maintaining good health.

Source: UCLA


Today’s Comic

Large Waist Linked to Poor Health, Even Among Those in Healthy Body Mass Index Ranges

Having a big belly has consequences beyond trouble squeezing into your pants. It’s detrimental to your health, even if you have a healthy body mass index (BMI), a new international collaborative study led by a Mayo Clinic researcher found. Men and women with large waist circumferences were more likely to die younger, and were more likely to die from illnesses such as heart disease, respiratory problems, and cancer after accounting for body mass index, smoking, alcohol use and physical activity. The study is published in the March edition of Mayo Clinic Proceedings.

The researchers pooled data from 11 different cohort studies, including more than 600,000 people from around the world. They found that men with waists 43 inches or greater in circumference had a 50 percent higher mortality risk than men with waists less than 35 inches, and this translated to about a three-year lower life expectancy after age 40. Women with a waist circumference of 37 inches or greater had about an 80 percent higher mortality risk than women with a waist circumference of 27 inches or less, and this translated to about a five-year lower life expectancy after age 40.

Importantly, risk increased in a linear fashion such that for every 2 inches of greater circumference, mortality risk went up about 7 percent in men and about 9 percent in women. Thus, there was not one natural “cutpoint” for waist circumference that could be used in the clinic, as risk increased across the spectrum of circumferences.

Another key finding was that elevated mortality risk with increasing waist circumference was observed at all levels of BMI, even among people who had normal BMI levels. Because of the large size of this pooled study, researchers were able to clearly show the independent contribution of waist circumference after accounting for BMI, says James Cerhan, M.D., Ph.D., a Mayo Clinic epidemiologist and lead author of the study.

“BMI is not a perfect measure,” says Dr. Cerhan. “It doesn’t discriminate lean mass from fat mass, and it also doesn’t say anything about where your weight is located. We worry about that because extra fat in your belly has a metabolic profile that is associated with diseases such as diabetes and heart disease.”

Dr. Cerhan says physicians should consider both BMI and waist circumference as part of risk assessment for obesity-related premature mortality.

“The primary goal should be preventing both a high BMI and a large waist circumference,” Dr. Cerhan says. “For those patients who have a large waist, trimming down even a few inches — through exercise and diet — could have important health benefits.”

Source: EurekAlert!

Why BMI Isn’t The Best Measure for Weight (or Health)

Body Mass Index (BMI) provides an easy way to measure obesity, but more doctors are questioning its accuracy and usefulness.

BMI is supposed to estimate the amount of body fat a person carries based on height and weight, and categorizes people based on what is appropriate for their size. BMI readings under 18.5 mean you are underweight, and could put on a few pounds. If you fall between 18.5 and 24.9, you’re considered normal, while a BMI of 30 or higher qualifies as overweight.

But in recent years, more researchers argue that it’s not the most accurate way to measure body weight. For years, scientists have said that BMI can’t distinguish between fat and muscle, which tends to be heavier and can tip more toned individuals into overweight status, even if their fat levels are low. In the journal Science, the latest data from University of Pennsylvania shows that BMI also doesn’t tease apart different types of fat, each of which can have different metabolic effects on health. BMI cannot take into consideration, for example, where the body holds fat. Belly fat, which is known as visceral fat, is more harmful than fat that simply sitting under the skin. Visceral fat develops deep among muscles and around organs like the liver and by releasing certain hormones and other agents, it disrupts the body’s ability to balance its energy needs. Even relatively thin people can have high levels of visceral fat, which means they might be considered healthy by BMI standards, but internally they may actually be at higher risk of developing health problems related to weigh gain.

In April of last year, a study published in the journal PLoS One documented such inconsistencies and questioned the accuracy of using BMI to classify weight status of 1,400 men and women. As TIME reported:

Among the study participants, about half of women who were not classified as obese according to their BMI actually were obese when their body fat percentage was taken into account. Among the men, in contrast, about a quarter of obese men had been missed by BMI. Further, a quarter who were categorized as obese by BMI were not considered obese based on their body fat percentage. Overall, about 39% of participants who were classified as overweight by their BMI were actually obese, according to their percent body fat.

So why is BMI still the preferred way to measure weight and evaluate obesity? For one, it’s a relatively easy measurement for doctors to take during an office visit. Taking a person’s height and weight and plugging it into an equation produces a number that informs doctors about whether their patients are at high, low or no risk when it comes to weight-related health problems.

But there may be better ways to measure body fat that provide more useful readings on how likely a person’s weight will contribute to chronic health problems. CT scans and MRIs can provide a clearer glimpse at the body’s make-up by separating out fat from muscle, for example. But these are expensive and involved compared to stepping on a scale. Other types of scans, including dual-energy X-ray absorptiometry (DEXA) images, which are normally used to measure bone density, can also distinguish between fat from bone and muscle mass, but are also costly.

On the more practical level, some researchers have been pushing for using waist circumference or even wrist circumference to gauge potentially harmful weight gain and fat depots, but the evidence supporting this measurement and its ability to predict future health problems isn’t definitive enough yet.

So without a viable way to change how we measure body fat, for now, BMI is the best option. The study authors argue that perhaps doctors should rely on not just assessing body composition but measuring hormones and biomarkers in the blood or urine, for example, to get a better handle on abnormal processes that may contribute to obesity and chronic disease. And until such tests become available, BMI may still prove useful yet — if doctors combine BMI with a comprehensive evaluation of their patients’ medical history and lifestyle habits to get a meaningful, if not yet perfectly precise picture of their weight-related health.

Source: Time