Body Fat More Accurately Predicts Heart Disease, Death Risk Than BMI

Health Line

21 hours ago

A new study reports that measurements that detect body fat are a more accurate predictor of mortality risk than body mass index (BMI).
Experts say BMI doesn't differentiate between weight attributed to body fat and weight attributed to muscle.
They do note that BMI is easier to calculate and less expensive than many body fat measurements.
Body mass index (BMI) only tells part of the story when it comes to determining your overall health and death risk.
Measurements that calculate body fat percentage are significantly more accurate for determining health profiles, according to a new study published Annals of Family Medicine.
Compared to BMI scores, researchers said body-fat percentages were a stronger predictor of the 15-year mortality risk of young adults ages 20 to 49.
They reported that people with high body fat are 78% more likely to die from any cause compared to people without high body fat.
In addition, those with elevated body fat percentages have a 262% higher chance of dying from heart disease.
The researchers said BMI measurements did not detect these risks, but other measurements did. These included bioelectrical impedance analysis (BIA), which uses electrical current to measure body fat, muscle mass, and water weight.
'Body fat percentage is a better predictor of 15-year mortality risk factor in young adults than BMI. A move to using [body fat percentages] rather than BMI may change how we measure body composition for risk stratification,' the researchers wrote.
For their study, the researchers analyzed data on 4,252 males and females who participated in the 1994 to 2004 National Health and Nutrition Examination Survey (NHANES). They then compared those records with data from the National Death Index through 2019.
Experts not involved in the study say the results are not surprising.
'Previous studies have shown similar results — measuring body fat, especially fat deep in the belly which is close to organs, more metabolically active and plays a greater metabolic risk, may be a better assessment than simply a number on the scale which cannot assess variations between muscle, fat, water, etc.,' said Kristin Kirkpatrick, RD, the president of KAK Consulting and a dietitian at the Cleveland Clinic Dept of Department of Wellness & Preventive Medicine.
BMI is more accessible but not as accurate
The concept of body mass index (BMI) was developed in 1832 by Belgian mathematician Lambert Adolphe Jacques Quetelet.
It's calculated by basically dividing a person's weight by their height squared. There are free calculators online to help do the math.
Using that scale, medical professionals classify body composition of adults in the following way.
less than 18.5 — underweight
18.5 to 24.9 — healthy weight
25 to 29.9 — overweight
30 or greater — obesity
Obesity is classified by three subtypes using BMI:
class 1 obesity — 30 to 34.9
class 2 obesity — 35 to 39.9
class 3 obesity — 40 or higher
Ali said the advantages of measuring BMI are that it's a well-known gauge that is easy to calculate, relatively inexpensive, and generally accepted by insurance.
Some past studies have shown that BMI can be a predictor of chronic diseases such as:
type 2 diabetes
cancer
kidney disease
Mir Ali, MD, a general surgeon, bariatric surgeon, and the medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in California, said BMI doesn't distinguish between weight obtained by muscle and weight due to body fat.
'It doesn't take into account the differences between fat and muscle in the body,' Ali told Healthline. 'BMI is not necessarily the best measurement for body composition — it's more of a guidance.'
Becca Krukowski, PhD, a professor of public health services at the University of Virginia and a fellow at the Obesity Society, said BMI measurements have several shortcomings.
'BMI is widely used in clinical settings because it is easy to compute,' she told Healthline.
'However, BMI is a rough measure of body composition, and individuals can be misclassified with overweight or obesity if they are extremely muscular. In addition, someone with a BMI in the 'normal' category could still have a high body fat percentage, which still increases their risk of many chronic diseases,' Krukowski continued.
Kirkpatrick expressed similar concerns.
'BMI may offer a general assessment — and the location of fat in the body matters related to risk, [but] the major disadvantage [of BMI] is not being able to assess health risk simply based on the number,' she told Healthline.
Measuring body fat percentage
In their study, researchers said bioelectrical impedance analysis bioelectrical impedance analysis (BIA) is a more accurate way of predicting future health issues.
This system works by sending small electric currents throughout the body. Electrodes on the skin measures these currents after they pass through body tissues. These currents move easier through muscle than fat.
Other methods of measuring body fat include dual-energy X-ray absorptiometry (DEXA) and body circumference measurements.
Kirkpatrick said these types of body fat measurements provide a better overall picture.
'[Body fat] assessment (and looking at where fat is stored) can help assess risk,' she explained.
'For example, fat stored in the belly is much more dangerous in terms of metabolic risk than fat that is stored in the thighs and buttocks. Genetics play a role as well, with some individuals having more risk based on other factors.'
Ali agreed. 'Body fat may be a better measurement of overall health,' he said, noting the disadvantages of these types of measurements are that they can be more expensive and they aren't as easy to calculate as BMI.
Krukowski noted similar limitations. 'Each of these methods have their pros and cons,' she said.
'Dual-energy X-ray absorptiometry (DEXA) scans are very accurate, but quite expensive and not available in many clinical settings. Although waist circumference measurement can be quite helpful in predicting disease risk, it is very complicated to do correctly. Finally, as the authors note in the article, bioelectrical impedance analysis machines have not always been able to provide accurate measurement of body fat percentage,' Krukowski continued.
'However, this article indicates that perhaps this bioelectrical impedance analysis technology has improved enough to seriously consider this technology in estimating body fat percentage,' she added.
Ali noted there are simple ways for people to assess their overall health, too. For example, if you have trouble walking up stairs or standing up after kneeling, your overall health may not be where it should be.
Obesity and health risks
The Centers for Disease Control and Prevention (CDC) estimates that 40% of U.S. adults have obesity.
The condition has a higher prevalence in people in certain groups, including non-Hispanic Black adults and people with less education.
There are many health risks associated with obesity. Among them:
heart disease
stroke
high blood pressure
liver disease
certain cancers
pregnancy complications
Experts say you can lower your risk of obesity by following a healthy lifestyle of exercise and diet.
For exercise, it's recommended to aim for at least 150 minutes a week of moderate aerobic activity.
For diet, experts advise:
filling half your plate with vegetables
eating more whole grains
choosing lean sources of protein (i.e., chicken and seafood)
avoiding fried foods
avoiding sugary foods
avoiding or abstaining from alcohol
'Body weight is just one component of fitness and health,' said Kirkpatrick. 'Dietary patterns, sleep, exercise habits, genetics, and environment all may play a role in an individual's health status.'