Do some fast math, and BMI — or physique mass index — looks as if the important thing to unlocking mysteries about your well being. But an increasing number of persons are beginning to query this weight-to-height ratio. (Tom Brady, solely the best quarterback of all time, has a BMI that places him within the obese vary!)
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So is BMI actually correct? Clinical psychologist Leslie Heinberg, PhD, is the director of Enterprise Weight Management for the Cleveland Clinic. In different phrases, she’s a weight and BMI skilled. Dr. Heinberg explains the rise of BMI as a software to measure your well being — and whether or not to make use of it or lose it.
What is BMI?
BMI measures your weight-to-height ratio. “People who are taller tend to weigh more, so you can’t compare weight without taking height into consideration,” says Dr. Heinberg. “BMI is your weight in kilograms divided by your height in meters squared.”
BMI has been round for some time. (A Belgian mathematician named Lambert Adolphe Jacques Quetelet developed it in 1832.) Dr. Heinberg says researchers initially used BMI to explain giant teams of individuals, not particular person well being.
“But it really took off around the mid-20th century with actuaries,” she says. “They were looking to describe populations to determine things like risk and life insurance.”
Looking on the BMIs of such giant teams of individuals revealed some hard-to-ignore patterns. Certain BMI ranges had been related to higher dangers of illness, mortality and different poor outcomes. And so traces had been drawn — under this line, you’re “healthy”; above it, you’re “at-risk.”
“But it’s the same with any metric in medicine,” explains Dr. Heinberg. “Is there something magical with hypertension such that 120 over 80 is normal, and 121 over 81 is high blood pressure? No. But when we look at hundreds of thousands of people, there are differences at that line.”
How to measure your BMI
To calculate BMI, use this adult BMI calculator or these formulation:
- U.S. items: Weight in kilos ÷ top2 in inches) x 703 = BMI (for instance: 150 kilos ÷ 65 inches2 x 703 = 26.6)
- Metric items: Weight in kilograms ÷ top2 in meters = BMI (for instance: 70 kilograms ÷ 1.7 meters2 = 24.2)
If you end up out of the conventional vary, Dr. Heinberg says it’s an ideal place to begin for a chat together with your doctor.
“People don’t automatically need to reduce their BMI into the ‘normal range’ to see health benefits. Even dropping your BMI one or two points can significantly reduce the risk of conditions such as diabetes and cardiovascular disease.”
How correct is BMI?
File this one beneath “it’s complicated.” As your BMI rises, your danger for well being issues will increase as nicely. For instance, individuals who have BMIs within the obese vary are at greater danger for growing diabetes than individuals within the regular vary.
“That risk may be twice as high,” says Dr. Heinberg. “But when you look at people whose BMIs are more than 40, the risk may increase to 20 times higher.”
BMI is an train in well being chance. Does a excessive BMI imply you robotically have poor well being? No. Does it dramatically improve your danger of poor well being? Absolutely.
For instance, not everybody who has a BMI over 40 has diabetes. But many extra individuals with BMIs over 40 have diabetes than individuals within the obese or regular weight vary.
“A too-high or too-low BMI is not an ironclad guarantee that you will develop a chronic disease,” notes Dr. Heinberg. “Rather, it’s an important piece of information that you and your primary healthcare provider should look at within the context of evaluating you as a whole person.”
Why isn’t BMI correct in some instances?
Some exceptions could make BMI appear extra like a Magic 8 Ball, although. Factors that may make BMI not correct embrace:
Race and ethnicity
When it involves BMI, all races and ethnicities are lumped collectively — and that may result in unclear and complicated outcomes. More and extra analysis exhibits that there are organic and genetic variations within the relationship between weight, muscle mass and illness danger amongst completely different teams of individuals. BMI doesn’t account for that.
Certain genetic elements can have an effect on BMI accuracy due to their impact on weight distribution and muscle mass. For instance, a 2011 study confirmed that Black girls had much less metabolic danger at greater BMIs than white girls. Another confirmed that Mexican American girls are likely to have extra physique fats than white and Black girls.
Other analysis exhibits that for individuals of Asian or Middle Eastern descent, even a decrease BMI could also be deceptive. They have a better danger for metabolic ailments like diabetes at a decrease BMI than individuals of European descent.
“The cutoffs we use may miss some people who are high risk and may need earlier intervention,” Dr. Heinberg notes. “They might not get the preventive care they need since they look at their lower BMI and think, ‘Great, I’m in good health, I don’t need to do anything’.”
People who’re athletic are likely to have a better proportion of lean muscle mass and a decrease proportion of fats mass than the common inhabitants. These elements can throw a wrench of their BMI measurements. They may measure within the obese class (or greater) regardless of having nice general well being.
Being pear- or apple-shaped doesn’t simply have an effect on clothes preferences. “BMI does not take waist circumference into account,” explains Dr. Heinberg. “Two individuals can weigh the identical and, subsequently, have the identical BMI. But their danger for illness won’t be the identical.
“Say Person A has a higher waist circumference, carrying their weight in their abdomen. Person B carries their weight lower in their body. Person A has a higher risk of metabolic and cardiovascular disease, but their identical BMI doesn’t tell that story,” she notes.
Older adults are likely to have extra physique fats and fewer muscle mass — however that’s not essentially a foul factor. Studies present that BMIs within the high-normal to obese vary could shield older adults from growing sure ailments and dying early.
Does your BMI nonetheless matter?
Think of BMI like a puzzle piece: It’s part of your complete well being image. Other worthwhile items embrace:
- Blood stress: Blood pressure measures the stress of your blood in opposition to your artery partitions as your coronary heart beats. It’s indicator of coronary heart well being and coronary heart illness danger.
- Blood sugar: Blood sugar tests inform you how a lot glucose (sugar) is in your blood. They assist docs display for pre-diabetes and diabetes.
- Cholesterol: Your cholesterol levels present the quantity of LDL (unhealthy) and HDL (good) ldl cholesterol in your blood. Too a lot LDL will increase your coronary heart assault and stroke danger.
- Heart price: A excessive resting heart rate places you at elevated danger for heart attack and loss of life.
- Inflammation: Chronic inflammation is linked to ailments like most cancers, rheumatoid arthritis, coronary heart illness and Type 2 diabetes.
- Lean muscle mass versus fats mass: The next proportion of lean muscle mass can shield in opposition to weight problems and obesity-related circumstances, together with diabetes.
- Waist circumference: You have a better danger for growing obesity-related circumstances in case your waist circumference is greater than 40 inches (males) or greater than 35 inches (nonpregnant girls).
“Knowing a patient’s lean muscle mass versus fat mass may be more informative than BMI, but it’s hard to measure accurately and cheaply,” provides Dr. Heinberg. “Waist circumference can be exhausting to measure precisely, significantly in sufferers with higher weight problems.
“That’s one of the reasons we rely on BMI. All you need is a scale, stadiometer (which measures height) and calculator,” she says.
Dr. Heinberg’s take-home level: Even with its many exceptions, don’t throw the BMI child out with the bathwater.
“Blood pressure tells you about cardiovascular risk, but BMI tells you about risk for that and other conditions like cancer, endocrine disorders and sleep apnea,” says Dr. Heinberg. “Knowing someone has obesity based on BMI can lead to a more comprehensive evaluation with their doctor.”