What Your BMI Doesn’t Tell You
BMI's Drawbacks continued...
Your body type: Are you an apple shape or a pear shape? The location of your fat makes a difference to your health. Generally, it's the belly fat, or the "apple" shape, that has a higher health risk. When fat settles around the waist instead of the hips, the chance of heart disease and type 2 diabetes goes up. Fat that builds up on the hips and thighs, or the "pear" shape, isn't as potentially harmful.
Your age: The notion of an ideal BMI may shift with age. "People who are older probably should have a little more fat on them, [but] they shouldn't have a BMI of 30," Atkinson says.
He points out that 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 on when fighting off an illness. It's hard to tell for sure, since many things affect your health.
Your ethnicity: There are a lot of differences in BMI and health risk among ethnic groups. For example, Asian-Americans tend to develop health risks, including the risk of diabetes, at lower BMIs than whites. A healthy BMI for Asians ranges from 18.5 to 23.9, a full point lower than the standard range. And Asians are considered obese at a BMI of 27 or higher, compared to the standard BMI obesity measure of 30 or higher.
People of Indian descent face higher health risks at relatively lower BMIs, Atkinson says. "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."
In contrast, many African-Americans may have a high BMI, but without the health risks that usually go along with it. Compared to whites with the same weight and BMI, African-Americans tend to have less visceral fat (fat around their organs) and more muscle mass, Atkinson says. Therefore, an African-American with a BMI of 28, which the standard chart calls overweight, might be as healthy as a white person with a BMI of 25.
So what other tools can you use besides BMI? You may want to get out your measuring tape.
Waist size: For an accurate measurement, the tape measure should go around your waist at the top of your hip bones in your lower back and go around to the belly button.
To help prevent health problems from being overweight, men should keep their waist size to no more than 39 or 40 inches. Women should stick to no more than 34 or 35 inches. Again, there are some ethnic differences. Asian men should keep their waists no more than 35.5 inches and Asian women to no more than 31.5 inches, according to the Joslin Diabetes Center.
Waist-to-height ratio: This compares your waist measurement to your height. It may be even more helpful than waist circumference alone, Kahan says. The goal is for your waist circumference to be less than half of your height.