Why Your BMI Doesn't Tell the Whole Story
You may have heard of BMI -- body mass index. It's based on your height and weight, and it's widely used to say who's obese, who's overweight (but not obese), who's at a normal weight, and who's underweight. But BMI has some drawbacks. It may not be the best way to size up your shape. And it says nothing at all about your fitness level. So how useful is BMI really? And what else might you use?
I found this article on WEDMD and it’s well worth reading. I wrote a post a few days ago about BMI and how Doctors and insurance companies use it. So what’s important is that you understand how they’ll use this against you to increase the amount you have to pay.
What is BMI?
BMI, calculated from a person's height and weight, breaks down into four categories:
• Underweight: BMI below 18.5
• Normal: BMI ranging between18.5 and 24.9
• Overweight: BMI ranging between 25 and 29.9
• Obese: BMI of 30 or higher
"Probably for 90% or 95% of the population, BMI is just fine as a general measure of obesity," says Richard L. Atkinson, MD, director of the Obetech Obesity Research Center in Richmond ,Va.
But some critics take a different view. Scott Kahan, MD, MPH, director of the National Center for Weight and Wellness in Washington, D.C., and a faculty member of the George Washington University School of Medicine, believes that BMI has merit, particularly for scientific research.
"When you take a big population -- thousands of people, tens of thousands of people -- as part of a research study, it's extraordinarily difficult to use anything more advanced than BMI," he says. "BMI is cheap, it's quick, and on the whole, on the average, it gives a reasonable measure that can be useful in those situations."
But for you, or any other individual? BMI might not be the best.
Kahan specializes in helping patients manage excessive weight that can lead to health problems, including diabetes and heart disease. He notes that although BMI is useful as a quick screening tool by a doctor or nurse, it's not enough just to look at a number. "Traditionally, we define obesity by a certain cut-off on the BMI scale," he says. That amounts, he says, to judging whether a person is obese based only on that person's size, something Kahan calls "antiquated and not terribly useful."
BMI's Drawbacks
Your BMI is a number. It doesn't reveal anything about your body composition -- for example, how much muscle versus fat you have. That's why conclusions based only on BMI can be misleading, especially for the following groups:
Muscular people: Some people have high BMIs but don't have much body fat. Their muscle tissue pushes up their weight. People in the military who exercise daily might fall into this category, Atkinson says. Other examples: "A football player or a body builder who is very muscular. Their BMI shows up pretty high and yet their body fat is actually pretty low," Kahan says.
Frail or inactive people: Some people with BMIs that are in the normal range actually have lots of body fat though they may not look out of shape. Think of that as being fat on the inside.
"They have very low levels of muscle and bone -- often elderly people, those in poor shape, sometimes those who are sick. They tend to be somewhat frail. Their BMI can look in the normal range, even though they have quite a lot of body fat in comparison to their lean body mass," Kahan says. "Ultimately, they have similar risks as people who carry lots of body fat and have a high BMI."
Very inactive people who rarely exercise may be of normal weight and BMI but be "overfat," Atkinson says. "They don't have as much lean body mass as they should, and they have more fat than they should."
Ethnic differences: Major ethnic differences exist regarding BMI, but few people are aware of this fact, including some doctors, Kahan says. "It's certainly something that needs to be communicated better to the public and the health care community -- and in a way that people can do something about it."
For example, Asian Americans tend to develop health risks, including the risk of diabetes, at significantly lower BMIs than whites. According to the Joslin Diabetes Center in Boston, a healthy BMI for Asians ranges from 18.5 to 23.9, a full point lower than the standard range of 18.5 to 24.9.
For Asians, a BMI of 24 or more signals overweight, compared to the standard of 25. More strikingly, Asians are considered obese at a BMI of 27 or higher compared to the standard BMI obesity measure of 30 or higher.
Genetics plays a role in body fat, Atkinson says. Asian ethnic groups, from Japanese and Chinese to Cambodians and Indians from India, tend to lay down fat in the midsection, he says. "When they start gaining weight, they gain it first in their abdominal cavity."
People of Indian descent are at highest risk, according to Atkinson. "With a lot of Indians who come to the United States and start living the American lifestyle, their weight and BMI may not make them look fat, but they are particularly at risk," he says. "They have excess fat in their visceral cavity, in their abdominal fat, and that's associated with diabetes, hypertension, metabolic syndrome, and all those kinds of things."
"The standard definition of overweight is a BMI of 25 or above. But if you're from India, your risk of diabetes starts going up with a BMI of about 21 or 22," Atkinson says.
In contrast, many African-Americans may have high BMI measures, but no associated health risks, Kahan says. "Because African-Americans tend to have a little bit more lean body mass -- bone and muscle -- than, for example, Asian Americans, they very often have a deceptively higher BMI than other populations."
Compared to whites with the same weight and BMI, African-Americans tend to have less visceral fat and more muscle mass, Atkinson says. Therefore, an African-American person with a BMI of 28, which the standard chart defines as overweight, might be as healthy as a white person with a BMI of 25.
Age and BMI: The notion of an ideal BMI may shift with age. "People who are older probably should have a little more fat on them -- not obese, they shouldn't have a BMI of 30," Atkinson says. But, he points out, late in life, people who are "a little bit overweight" tend to have a better survival rate than leaner people. The reasons for that aren't totally clear, but it may have to do with having reserves to draw upon when fighting off an illness. However, it's hard to tell for sure since many factors affect someone's health.
Big BMI but Healthy Anyway?
Kahan sees some people who are fat but healthy; their BMI doesn't truly reflect their health risks.
Researchers describe such people as "MHO," or "metabolically healthy obese," Kahan says. "They're heavy, their BMI puts them in the obesity range, and yet, on every level that we look at, their health is actually quite good. Their cholesterol and blood pressure are excellent, their blood sugar is excellent. They don't seem to have any health effects associated with their excess weight."
Measuring BMI is only a starting point when patients come to Kahan's center. There are many other ways to assess their body fat and health risks, he says.
Where's the Fat?
Are you shaped more like an apple, or a pear? The location of your fat may make a difference to your health.
There are exceptions, but generally, it's the abdominal fat, or the "apple" shape, that's metabolically riskier. When fat settles around the waist instead of the hips, risk of coronary artery disease and type 2 diabetes is more likely, according to the NIH.
"That tends to be more metabolically active fat, or fat that deranges your metabolism and your health parameters and ultimately leads to more risk," Kahan says.
Fat that accumulates on the hips and thighs -- the "pear" shape -- isn't as potentially harmful. "Many women have lower body obesity, so their hips and thighs are larger, but their waists are not so big," Atkinson says. Fat lower down on the body doesn't carry the same risk as belly fat, he says.
Other Ways to Measure
What else is there besides BMI? You may want to get out your measuring tape.
Waist Size: This is as simple as it gets: wrapping a tape measure around your waist. For an accurate waist measurement, Kahan says the tape measure should encircle your waist at the top of your hip bones in your lower back and go around to the belly button.
Men should limit waist size to no more than 39 or 40 inches; women, no more than 34 or 35 inches, Atkinson says.
Again, there are some racial differences. For example, the Joslin Diabetes Center states that Asian men should keep their waists no more than 35.5 inches; Asian women, no more than 31.5 inches.
Is it useful? Yes. "The data show that waist circumference can be very valuable," Kahan says.
Waist-to-Height Ratio: This compares your waist measurement to your height. It may be even more helpful than waist circumference alone, according to Kahan. The goal is for your waist circumference to be less than half of your height.
Waist-to-Hip Ratio: This compares your waist measurement to your hip measurement. Kahan doesn't recommend this method. "We do have good data that using waist-to-hip ratio is not any more valuable than just using waist as a measurement," he says.
Bioelectrical impedance scales: These scales send electrical currents through the body to assess fat and lean mass. They may be useful, according to Atkinson.
There are also better methods to measure body fat, such as MRIs and DEXA scans. But for most people, scans are not practical. "These things are much more accurate, but they're much more expensive and much more difficult to do, so those are not likely to be reasonable options in the future," Kahan says.
It seems to me after reading this, that the BMI index that was invented in Belgium in 1832 is not practical in todays world. If it’s important to know the ratio between muscle and fat, we need a new index that works better for people’s lifestyle today. I do believe in a low ratio of fat to muscle. Also I believe that belly fat is the worst place to carry fat, it’s hard on your heart, your waist should measure half your height without exception.
I found this article on WEDMD and it’s well worth reading. I wrote a post a few days ago about BMI and how Doctors and insurance companies use it. So what’s important is that you understand how they’ll use this against you to increase the amount you have to pay.
What is BMI?
BMI, calculated from a person's height and weight, breaks down into four categories:
• Underweight: BMI below 18.5
• Normal: BMI ranging between18.5 and 24.9
• Overweight: BMI ranging between 25 and 29.9
• Obese: BMI of 30 or higher
"Probably for 90% or 95% of the population, BMI is just fine as a general measure of obesity," says Richard L. Atkinson, MD, director of the Obetech Obesity Research Center in Richmond ,Va.
But some critics take a different view. Scott Kahan, MD, MPH, director of the National Center for Weight and Wellness in Washington, D.C., and a faculty member of the George Washington University School of Medicine, believes that BMI has merit, particularly for scientific research.
"When you take a big population -- thousands of people, tens of thousands of people -- as part of a research study, it's extraordinarily difficult to use anything more advanced than BMI," he says. "BMI is cheap, it's quick, and on the whole, on the average, it gives a reasonable measure that can be useful in those situations."
But for you, or any other individual? BMI might not be the best.
Kahan specializes in helping patients manage excessive weight that can lead to health problems, including diabetes and heart disease. He notes that although BMI is useful as a quick screening tool by a doctor or nurse, it's not enough just to look at a number. "Traditionally, we define obesity by a certain cut-off on the BMI scale," he says. That amounts, he says, to judging whether a person is obese based only on that person's size, something Kahan calls "antiquated and not terribly useful."
BMI's Drawbacks
Your BMI is a number. It doesn't reveal anything about your body composition -- for example, how much muscle versus fat you have. That's why conclusions based only on BMI can be misleading, especially for the following groups:
Muscular people: Some people have high BMIs but don't have much body fat. Their muscle tissue pushes up their weight. People in the military who exercise daily might fall into this category, Atkinson says. Other examples: "A football player or a body builder who is very muscular. Their BMI shows up pretty high and yet their body fat is actually pretty low," Kahan says.
Frail or inactive people: Some people with BMIs that are in the normal range actually have lots of body fat though they may not look out of shape. Think of that as being fat on the inside.
"They have very low levels of muscle and bone -- often elderly people, those in poor shape, sometimes those who are sick. They tend to be somewhat frail. Their BMI can look in the normal range, even though they have quite a lot of body fat in comparison to their lean body mass," Kahan says. "Ultimately, they have similar risks as people who carry lots of body fat and have a high BMI."
Very inactive people who rarely exercise may be of normal weight and BMI but be "overfat," Atkinson says. "They don't have as much lean body mass as they should, and they have more fat than they should."
Ethnic differences: Major ethnic differences exist regarding BMI, but few people are aware of this fact, including some doctors, Kahan says. "It's certainly something that needs to be communicated better to the public and the health care community -- and in a way that people can do something about it."
For example, Asian Americans tend to develop health risks, including the risk of diabetes, at significantly lower BMIs than whites. According to the Joslin Diabetes Center in Boston, a healthy BMI for Asians ranges from 18.5 to 23.9, a full point lower than the standard range of 18.5 to 24.9.
For Asians, a BMI of 24 or more signals overweight, compared to the standard of 25. More strikingly, Asians are considered obese at a BMI of 27 or higher compared to the standard BMI obesity measure of 30 or higher.
Genetics plays a role in body fat, Atkinson says. Asian ethnic groups, from Japanese and Chinese to Cambodians and Indians from India, tend to lay down fat in the midsection, he says. "When they start gaining weight, they gain it first in their abdominal cavity."
People of Indian descent are at highest risk, according to Atkinson. "With a lot of Indians who come to the United States and start living the American lifestyle, their weight and BMI may not make them look fat, but they are particularly at risk," he says. "They have excess fat in their visceral cavity, in their abdominal fat, and that's associated with diabetes, hypertension, metabolic syndrome, and all those kinds of things."
"The standard definition of overweight is a BMI of 25 or above. But if you're from India, your risk of diabetes starts going up with a BMI of about 21 or 22," Atkinson says.
In contrast, many African-Americans may have high BMI measures, but no associated health risks, Kahan says. "Because African-Americans tend to have a little bit more lean body mass -- bone and muscle -- than, for example, Asian Americans, they very often have a deceptively higher BMI than other populations."
Compared to whites with the same weight and BMI, African-Americans tend to have less visceral fat and more muscle mass, Atkinson says. Therefore, an African-American person with a BMI of 28, which the standard chart defines as overweight, might be as healthy as a white person with a BMI of 25.
Age and BMI: The notion of an ideal BMI may shift with age. "People who are older probably should have a little more fat on them -- not obese, they shouldn't have a BMI of 30," Atkinson says. But, he points out, late in life, people who are "a little bit overweight" tend to have a better survival rate than leaner people. The reasons for that aren't totally clear, but it may have to do with having reserves to draw upon when fighting off an illness. However, it's hard to tell for sure since many factors affect someone's health.
Big BMI but Healthy Anyway?
Kahan sees some people who are fat but healthy; their BMI doesn't truly reflect their health risks.
Researchers describe such people as "MHO," or "metabolically healthy obese," Kahan says. "They're heavy, their BMI puts them in the obesity range, and yet, on every level that we look at, their health is actually quite good. Their cholesterol and blood pressure are excellent, their blood sugar is excellent. They don't seem to have any health effects associated with their excess weight."
Measuring BMI is only a starting point when patients come to Kahan's center. There are many other ways to assess their body fat and health risks, he says.
Where's the Fat?
Are you shaped more like an apple, or a pear? The location of your fat may make a difference to your health.
There are exceptions, but generally, it's the abdominal fat, or the "apple" shape, that's metabolically riskier. When fat settles around the waist instead of the hips, risk of coronary artery disease and type 2 diabetes is more likely, according to the NIH.
"That tends to be more metabolically active fat, or fat that deranges your metabolism and your health parameters and ultimately leads to more risk," Kahan says.
Fat that accumulates on the hips and thighs -- the "pear" shape -- isn't as potentially harmful. "Many women have lower body obesity, so their hips and thighs are larger, but their waists are not so big," Atkinson says. Fat lower down on the body doesn't carry the same risk as belly fat, he says.
Other Ways to Measure
What else is there besides BMI? You may want to get out your measuring tape.
Waist Size: This is as simple as it gets: wrapping a tape measure around your waist. For an accurate waist measurement, Kahan says the tape measure should encircle your waist at the top of your hip bones in your lower back and go around to the belly button.
Men should limit waist size to no more than 39 or 40 inches; women, no more than 34 or 35 inches, Atkinson says.
Again, there are some racial differences. For example, the Joslin Diabetes Center states that Asian men should keep their waists no more than 35.5 inches; Asian women, no more than 31.5 inches.
Is it useful? Yes. "The data show that waist circumference can be very valuable," Kahan says.
Waist-to-Height Ratio: This compares your waist measurement to your height. It may be even more helpful than waist circumference alone, according to Kahan. The goal is for your waist circumference to be less than half of your height.
Waist-to-Hip Ratio: This compares your waist measurement to your hip measurement. Kahan doesn't recommend this method. "We do have good data that using waist-to-hip ratio is not any more valuable than just using waist as a measurement," he says.
Bioelectrical impedance scales: These scales send electrical currents through the body to assess fat and lean mass. They may be useful, according to Atkinson.
There are also better methods to measure body fat, such as MRIs and DEXA scans. But for most people, scans are not practical. "These things are much more accurate, but they're much more expensive and much more difficult to do, so those are not likely to be reasonable options in the future," Kahan says.
It seems to me after reading this, that the BMI index that was invented in Belgium in 1832 is not practical in todays world. If it’s important to know the ratio between muscle and fat, we need a new index that works better for people’s lifestyle today. I do believe in a low ratio of fat to muscle. Also I believe that belly fat is the worst place to carry fat, it’s hard on your heart, your waist should measure half your height without exception.
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